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Allelochemicals: Sources, toxicity and microbial transformation in soil - A review
Abstract
Soil microorganisms interact with plants in diversified manner ranging from mobilising nutrients and enhancing their growth,
to inducing diseases. They also produce allelochemicals directly or indirectly through conversion from other compounds. In
order to hamper plant growth, allelochemicals must accumulate and persist at phytotoxic levels in the rhizosphere soil. However,
after their entry into environment, persistence, availability and biological activities of allelochemicals are influenced
by microorganisms. Transformation of allelochemicals by soil microbes may result into the compounds with modified biological
properties. Such bio-transformations affect the overall allelopathic capability of the producer plant in a direct manner.
Several reports describe the allelopathic significance of microbial metabolism products. For instance, a bacteriumActinetobacter calcoaceticus, can convert 2 (3H)-benzoxazolinone (BOA) to 2,2′-oxo-l,l′-azobenzene (AZOB) which is more inhibitory to some plants. On
the contrary, bacteriumPseudomonas putida catabolises juglone in soils beneath walnut trees; otherwise, juglone accumulates at phytotoxic levels. This review article
describes the nature of microbially produced allelochemicals, and the ways to mediate microbial degradation of putative allelochemicals.
The given information develops an understanding of persistence, fate and phytotoxicity of allelochemicals in the natural environment,
and also points out the possible solution of the problems due to microbial interventions in the soil.
... The CC of P. ternata will not only cause aggravation of pests and diseases, soil salinization and acidification, but also reduce the photosynthetic performance of leaves [7] and the activity of antioxidant enzymes of the plant, lead to membrane lipid peroxidation damage [8,9], ultimately resulting in the yield and quality decline of P. ternata. Investigations have shown that changes in soil physicochemical properties, nutrient decline, soil microbial community structure imbalance, accumulation of soil-borne pathogens and phenolic acid allelochemicals can all result in CCO [10][11][12]. Even under normal management practices, the yield of P. ternata after 2-4 years of continuous cropping (CC) is generally reduced by 80-90% [13]. ...
... In addition, these allelochemicals autotoxins are also the main substances that cause CCO in other staple crops, such as Arachis hypogaea [15,16], Glycine max [17], and Radix pseudostellariae [18]. Plants can release allelochemicals into the environment through a variety of pathways, for instance volatilization, leaching, residue decomposition and root secretion [11]. However, studies on the biodegradation of these allelochemicals in CC soil of P. ternata and the selective shaping of the rhizosphere microflora of P. ternata as well as how to jointly affect the growth and development of P. ternata have not been reported yet. ...
Background
Pinellia ternata (Thunb.) Breit. is a commonly used herb in traditional Chinese medicine, and the main raw material of various Chinese patent medicines. Continuous cropping obstacle (CCO) is the main factor leading to the decline of crop yields and quality.
Methods
Metagenomics sequencing technology was used to analyze the microbial community and functional genes of continuous cropping (CC) and control (CK) soils of P. ternata . In addition, differences in physicochemical properties, enzyme activities, microbial community composition and the abundance of functional genes in CC and CK were evaluated, as well as the relationship between these factors and CCO.
Results
Results indicated that CC of P. ternata led to the decline of rhizosphere soil pH, nutrient imbalance and enzyme activity reduction. Metagenomic analysis indicted that CC also changed the composition of the microbial community, causing an increase in the relative abundance of pathogenic microorganisms such as Fusarium , Klebsiella oxytoca and Pectobacterium carotovorum in the P. ternata rhizosphere. The relative abundance of potentially beneficial Burkholderia and Bradyrhizobium was recorded to decrease. Results also showed that there were considerable differences in CC and CK about the abundances of functional genes related to soil enzymes and the degradation of P. ternata allelochemicals, as well as the microbial groups which they belong. These results clarified the effects of CC on the microbial community structure and functional genes of soil. In addition, Burkholderia and Bradyrhizobium might play important roles in enhancing soil fertility and reducing the toxicity of phenolic acids in rhizosphere soil.
Conclusions
CC of P. ternata changed the physicochemical properties, microbial community and functional genes of rhizosphere soil. Burkholderia and Bradyrhizobium for enhancing soil fertility and reducing the toxicity of phenolic acids might be potentially beneficial. These results provide theoretical guidance for bioremediation of CCO soil of P. ternata and other staple crops.
Graphic abstract
... Lastly, microorganisms play a crucial role in minimizing the toxic effects of allelochemicals produced by invasive plants through degradation or transformation (Vidal and Bauman, 1997;Jilani et al., 2008). In such cases, plant growth performance can be expected better in the unsterile soils. ...
The role of alien invasive plants on the interaction between native plants and soil has been a critical concern for understanding invasion mechanism and response of native plants towards invasion. This study aims to analyze the effect of invaded soils by an invasive Siam weed (Chromolaena odorata (L.) R.M. King & H. Rob.) under sterilized and unsterilized conditions on growth performance of seedlings of a valuable native Sal tree (Shorea robusta Gaertn. f.). For the analysis, seedlings of S. robusta were grown in pots and growth parameters were measured. Results showed that the C. odorata invaded soil reduces the root biomass, leaf length and leaf breadth of S. robusta seedlings. Sterilization of the invaded increased root and shoot and leaf size of the seedlings. In conclusion, soil sterilization can promote early-stage growth for S. robusta seedlings, adjusting with altering the shape and size of leaves in response to invasion. This suggests that soil microbes play an important role in negatively impacting native plants with invasion of C. odorata.
... During the cultivation process, P. ternata can release allelochemicals into the environment through root secretion and litter decomposition (Jilani et al. 2008;Tang et al. 2018). The content of total phenolic acid (TPA) in B2 group was significantly higher than Plant Soil Vol:. ...
Background and aims
The continuous cropping obstacle (CCO) of Pinellia ternata has led to a sharp decline in both yield and quality, while the absence of effective mitigating measures seriously hinders the sustainable development of the industry. In this study, a microbial agent (MA) was applied to remit the CCO of P. ternata.
Methods
A microbial agent consisted of microbes with the function of allelochemical degradation, phosphate and potassium solubilization and nitrogen fixation was inoculated into the CCO soil of P. ternata. The growth condition and yield of tubers, physicochemical properties and microbial community of rhizosphere soil were determined.
Results
After inoculation, the growth and yield of P. ternata and the degradation of total phenolic acid were promoted, and the properties of soil were also improved, including pH value, organic matter content, concentration of nitrogen, phosphorus, and potassium, as well as the activity of urease, catalase, polyphenol oxidase and sucrase. In addition, the soil microbial community composition was optimized by the application of MA through increasing the abundance of beneficial microbes and inhibiting that of pathogens such as Fusarium. Moreover, the abundance of functional genes related to soil enzyme activity, allelochemicals degradation, nitrogen fixation, phosphorus and potassium solubilization, and plant growth promoting were also significantly increased after inoculation. Finally, the composition of MA was simplified according to the microbial colonization status, functional genes and the correlation analysis.
Conclusion
This study provided theoretical and technical guidance to alleviate the CCO of P. ternata and propose in-depth insights of the interactions among P. ternata, soil, and microbes.
... The allelopathic effect suggested here may have occurred directly or indirectly (i) through chemical modifications of litter by microorganisms during their decay, allowing a phytotoxic effect to occur in the soil (Jilani et al. 2008), or (ii) through the modification of microbial communities exposed to allelochemicals or by-products that caused unfavorable conditions for plant growth or survival in the soil, by limiting nutrient absorption for example (Inderjit 2003;Scavo, Abbate, and Mauromicale 2019). Moreover, allelochemicals can influence not only their plant neighbors but also fungi and bacteria (Schandry and Becker 2020), which can ultimately affect competition for resources between these organisms (mainly saprophytic microbes) and plants in the context of litter decomposition. ...
Aims
Dominant or pioneer species litter decomposition was found to be involved in the recruitment of following species during succession in terrestrial plant communities, while knowledge remains scarce in wetland forests such as mangroves. Our study evaluated the influence of pioneer species leaf litter decomposition on (i) the settlement success of species following them or not in the natural succession and (ii) on soil characteristics.
Location
Red River Delta, Vietnam.
Methods
We set up an in situ experiment in mesocosms that followed the survival and growth of three species ( Kandelia obovata , Aegiceras corniculatum , and Rhizophora stylosa ) planted in soils of Avicennia marina or Sonneratia caseolaris , with or without leaf litter addition for 203 days. Soil nutrient contents were determined at the beginning and end of the experiment, and their metabolic fingerprints were compared using an untargeted metabolomic approach to highlight potential allelochemicals when a phytotoxic effect was observed.
Results
Seedling response to litter addition was species‐specific, which can be linked to their successional status. K. obovata was most affected by litter addition, showing better growth with both litter types. Meanwhile, A. marina litter substantially decreased survival rates by 50% for K. obovata and 33% for R. stylosa, suggesting a strategy to delay its replacement by these species through the release of phytotoxic decomposition by‐products. Metabolic fingerprints of A. marina soils planted with K. obovata showed no shift in global chemical composition, but 12 features were found significantly more abundant in the presence of litter. Putative annotations revealed sulfur‐containing metabolites, which are probable products of organic matter sulfurization, a frequently occurring process in mangrove sediments. These unusual compounds may act as allelochemicals and should be further assessed.
Conclusions
Our findings suggest that allelopathic processes through litter decomposition may be at play in mangrove community assembly and could be a tool for restoration purposes.
... A second example is a mixture of ginsenosides of lower molecular weight and low polarity (due to the microbial hydrolysis of glycosidic bonds) that inhibits root growth and alters the expression of over 6500 ginseng genes, including those for phenylpropanoid synthesis [17]. While those allelochemicals have been found in ginseng root, it is possible that there are a number of allelochemicals that can undergo transformation by soil microbes into active forms, such as by the oxidation and polymerization of phenolics [18]. Another possible ginseng-related factor in GRD is the unknown compounds extractable by methanol from soil one year following P. quinquefolius harvesting that increase lesion sizes by I. morspanacis and suppress gene expression related to jasmonate-regulated root defenses but are undetectable in ginseng roots or soil not previously planted with P. quinquefolius [3]. ...
A previous report showed that methanol extracts from soil collected one year after harvesting American ginseng (Panax quinquefolius) contained activity that increased root rot caused by Ilyonectria mors-panacis. This effect was associated with suppression of the defense responses of P. quinquefolius. The activity was undetectable in soil not previously planted with ginseng, and it was hypothesized that it may be a factor in the development of ginseng replant disease (GRD). GRD can persist for 30 or more years and is associated with root rot from I. mors-panacis. A survey of activity that increases root rot was made of the soil at different times before and after commercial ginseng root harvesting. No activity that increased root rot from I. mors-panacis was detected in the soil of a first American ginseng crop over the three years from planting until prior to harvesting. After harvesting the first crop, no activity was detected during the fall or early spring, but I. mors-panacis’s ability to increase root rot was detected in the soil during late spring, when ginseng crop debris from the first crop had almost completely decayed and the soil had warmed. Activity increasing root rot from I. mors-panacis was also detected in the soil from 1 to 30 years after ginseng harvesting. These results indicate that activity in soil that increases root rot from I. mors-panacis is not detectable until after the crop has been first harvested and then can persist for many years, which is consistent with the long persistence of GRD.
... The fresh leaves may contain greater amounts of lipiferolide than fallen leaves because 12 mg and 4 mg of lipiferolide were isolated from the fresh and fallen leaves, respectively. One of the reasons for the lower amount of lipiferolide in the fallen leaves may be the metabolism of the compound during the defoliation and/or degradation process of the leaves [67][68][69][70]. The concentrations of lipiferolide in the fresh and fallen leaves are consistent with the allelopathic activity of the extracts and powder obtained from the fresh and fallen leaves (Figures 3-6). ...
Logging operations of Liriodendron tulipifera L., as timber trees, and fallen leaves in autumn from ornamental trees produce a large amount of leaf waste. In this study, the allelopathy of L. tulipifera fresh and fallen leaves was investigated for the development of potential applications of leaf waste. The extracts of fresh and fallen leaves of L. tulipifera showed growth inhibitory activity against weed species, Vulpia myuros (L.) C.C.Gmel., Echinochloa crus-galli (L.) P.Beauv., and Lolium multiflorum Lam., under laboratory conditions. The powder of L. tulipifera fresh and fallen leaves also inhibited the germination of E. crus-galli under greenhouse conditions. A potent allelochemical was isolated from fresh and fallen leaf extracts through a bioassay-guided separation process, and was identified as lipiferolide. Lipiferolide inhibited the growth of L. multiflorum and Lepidum sativum in a concentration-dependent manner. This investigation suggests that the leaf waste of L. tulipifera from logging operations and fallen leaves is potentially useful for the purpose of weed control, such as through the use of soil additive materials from leaves or the creation of foliar spray from leaf extracts. The development of weed control materials using L. tulipifera leaf waste may be a means with which to minimize waste, reducing environmental impacts and economic concerns.
... In our study, heavy fertilization resulted in significant short-term changes in the soil environment. In addition, the accumulation of allelochemicals released by plant roots may inhibit the growth of some bacteria, leading to decreased bacterial diversity [55,56]. Therefore, changes in bacterial diversity are a response to alterations in the soil environment but are not a necessary factor underlying tomato Fusarium wilt. ...
Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici has severely threatened sustainable greenhouse tomato production. However, the effects of nutrient enrichment due to excessive fertilization on Fusarium wilt remain unclear. This study aimed to investigate the relationships among soil nutrient enrichment, microbial community structure, and the occurrence of Fusarium wilt under greenhouse conditions. This study used chemical analysis and microbiological techniques to analyze rhizosphere soil samples from greenhouse tomato production areas with varying degrees of Fusarium wilt. The results showed that, as compared with the Health group, the rhizosphere soil of Disease group has a significant nutrient enrichment, which significantly influences bacterial diversity and structure. Particularly when soil NO3⁻–N content exceeds 170.43 mg kg⁻¹, there was a significant reduction in the relative abundance of key biocontrol bacteria such as Bacillus and Lysinibacillus. This reduction indirectly contributes to an increase in Fusarium oxysporum abundance, subsequently elevating the likelihood of pathogen infection. Furthermore, the Disease group also exhibited a simplified co-occurrence network with a 22.37% reduction in competitive interactions between bacteria and fungi. These changes might collectively increase the risk of tomato Fusarium wilt infection. Meanwhile, the relative abundance of bacteria carrying antibiotic resistance genes significantly increased in the Disease group, which also reduced soil resistance. Together, the results presented here not only uncover the effect of long-term excessive fertilization on the occurrence of Fusarium wilt but also advance our understanding of the interactions among soil nutrient management and microbial communities in the tomato rhizosphere, which provides a scientific basis for formulating strategies to prevent soil-borne diseases in greenhouse tomatoes.
... Agrawal et al. 2012) and plant-associated microbes (Bennett et al. 2006). Soil microbes are known to be an important determinant of allelopathic effects as they might either degrade allelopathically active compounds exuded by plants or change them into even more potent ones (Weidenhamer and Romeo 2004;Inderjit 2005;Jilani et al. 2008;Cipollini et al. 2012). However, this phenomenon cannot explain our findings, because we tested the effects of microbes during growth of the allelopath (Solidago) and not during the test for allelopathy. ...
Background and aims
Plant investment in secondary metabolites can be driven by abiotic factors such as nitrogen (N) availability and variation in biotic factors such as root-associated microbes. However, few studies have tested their combined effect on allelopathy. Here, we test whether and how N addition (i.e. eutrophication) and soil microbes modify allelopathic effects of the invasive plant Solidago canadensis on germination of the native plant Crepidiastrum sonchifolium.
Methods
We first grew Solidago at three N levels with a live or sterilized soil inoculum. Then we exposed seeds of Crepidiastrum to aqueous extracts made of the Solidago plants. We analysed the biomass, soil microbiome (bacteria and fungi), and flavonoid, phenolic and saponin contents of Solidago, and the effects of the aqueous extracts on germination of Crepidiastrum.
Results
We found that Solidago produced 67% more biomass on live soil than on sterilized soil, and that N addition only resulted in more biomass on live soil. Soils that had been sterilized accumulated higher relative abundances of bacteria involved in N transformation, and tended to have higher relative abundances of pathotrophic fungi. When grown in soil that had been sterilized, the total flavonoid content of Solidago was 22% higher, and the aqueous extracts had stronger negative allelopathic effects on germination of Crepidiastrum.
Conclusion
The presence of natural soil microbial communities may enhance invasiveness of Solidago by promoting its growth and thereby competitive ability, but may simultaneously decrease the negative allelopathic impact on native neighbors.
... Various food and fodder crops are known to produce allelochemicals, that is, wheat, maize, rice, oats, barley, lupins, beet, rye, brassica, sorghum, and sunflower (Saxena et al. 2016 ). Roots of rye produce phenolics, 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), 6-methoxy-benzoxazolinone (MBO A), 2-benzoxazolinone (BO A), and hydroxamic acids (Reberg-Horton et al. 2005 ;Jilani et al. 2008 ). Microbial degradation in soil converted 2-BOA to 1-azobenzene (AZOB), which is more toxic and inhibitory to plants than DIBOA (Chase et al. 1991 ). ...
Weed infestation is one of the most damaging biotic factors to limit crop production by competing with the crop for space, water, and nutrients. Different conventional approaches are being used to cope with weed infestation including labor intensive manual removal and the use of soil-degrading and crop-damaging, and environment-deteriorating chemical herbicides. The use of chemicals for weed control has increased two-fold after the Green Revolution and their non-judicious use is posing serious threats to mankind, animals, and biodiversity. The detrimental effects of these approaches have shifted the researchers’ attention from the last two decades towards alternate, sustainable, and ecofriendly approaches to cope with weed infestation. The recent approaches of weed control including plant and microbial allelopathy have gained popularity during last decade. Farmers still use conventional methods, but the majority of farmers are very passionate about organic agriculture and describe it as a slogan in the developed world. The effectiveness of these approaches lies in host specificity by selective bacteria and differential response towards weeds and crops. Moreover, the crop growth promoting effect of microorganisms (allelopathic bacteria) possessing various growth promoting traits i.e., mineral solubilization, phytohormone production and beneficial enzymatic activity, provide additional benefits. The significance of this review lies in the provision of a comprehensive comparison of the conventional approaches along with their potential limitations with advanced/biological weed control approaches in sustainable production. In addition, the knowledge imparted about weed control will contribute to a better understanding of biological control methods.
... Considerations for the rhizosphere include microbes, nearby plants, organic and inorganic materials, pH, consistency, and moisture content [31]. Prior to reaching the target species, these conditions may have an impact on the physiochemical nature of allelopathins in the rhizosphere and consequently their phytotoxic activity [32][33][34]. The required concentration of potent allelopathins must therefore be examined under edaphic scenario in order to precisely determine their phytotoxicity [35]. ...
Chemical herbicides are the primary weed management tool, although several incidencesof herbicide resistance have emerged, causing serious threat to agricultural sustainability.Plant derived phenolic acids with herbicidal potential provide organic and eco-friendly sub-stitute to such harmful chemicals. In present study, phytotoxicity of two phenolic com-pounds, ferulic acid (FA) and gallic acid (GA), was evaluated in vitro and in vivo againstthree prevalent herbicide-resistant weed species (Sinapis arvensis, Lolium multiflorum andParthenium hysterophorus). FA and GA not only suppressed the weed germination (80 to60% respectively), but also negatively affected biochemical and photosynthetic pathway ofweeds. In addition to significantly lowering the total protein and chlorophyll contents of thetargeted weed species, the application of FA and GA treatments increased levels of antioxi-dant enzymes and lipid peroxidation. Photosynthetic gene (psbA) expression was downre-gulated (10 to 30 folds) post 48 h of phenolic application. In silico analysis for receptoridentification of FA and GA in psbA protein (D1) showed histidine (his-198) and threonine(thr-286) as novel receptors of FA and GA. These two receptors differ from the D1 aminoacid receptors which have previously been identified (serine-264 and histidine-215) inresponse to PSII inhibitor herbicides. Based on its toxicity responses, structural analogs ofFA were also designed. Four out of twelve analogs (0.25 mM) significantly inhibited weedgermination (30 to 40%) while enhancing their oxidative stress. These results are uniquewhich provide fundamental evidence of phytotoxicity of FA and GA and their analogs todevelop cutting-edge plant based bio-herbicides formulation in future.
... Environmental conditions such as biotic or abiotic factors contribute toward structural modification of allelochemicals, when applied in soil (Jilani et al., 2008); thus, the initial concentrations of extracts play a predominant role in determining its phytotoxicity. For this purpose, we used 10, 15, and 20% plant extracts to evaluate their toxicity level for growth suppression in soil experiments. ...
The productivity of major field crops is highly compromised due to weed infestation. Inefficient weed management practices and undue and excessive use of chemical herbicides have drastically contaminated the environment and human health, in addition to resistance development in weed species. Therefore, utilization of allelopathic plants to explore phytochemicals as potent organic alternatives to such chemical herbicides has become indispensable. The current study evaluates the comparative bio-herbicidal potential of methanolic extracts of castor (Ricinus communis), artemisia (Artemisia santolinifolia), wheat (Triticum aestivum), and sorghum (Sorghum bicolor) to suppress growth of major weeds, i.e., wild mustard (Sinapis arvensis), Italian ryegrass (Lolium multiflorum), and carrot grass (Parthenium hysterophorus). The results demonstrated a concentration-dependent effect on weeds’ growth. Overall, in vitro seed germination was reduced from 60 to 100% in response to 5% (w/v) extract concentration. Significant reduction in radicle length, hypocotyl length, and fresh biomass of the weeds was also observed. A strong inhibitory effect was seen in in vivo pot experiments, revealing that application of 10–20% methanolic extracts induced permanent wilting and substantial reduction in the chlorophyll content of weeds along with 20–80% increase in oxidative stress. Artemisia showed the most significant allelopathic effect, on account of highest phenolic and flavonoid contents, followed by castor, wheat, and sorghum, against S. arvensis, L. multiflorum, and P. hysterophorus, respectively. Phytochemical analysis, through high-performance liquid chromatography (HPLC), also exhibited a correlation between extract’s phytotoxicity and their antioxidant potential due to their major constituents (rutin, quercetin, catechin, gallic acid, vanillic acid, syringic acid, ferulic acid, p-hydroxy benzoic acid, p-coumaric acid, and sinapic acid), among the total of 13 identified in methanolic fractions. Comprehensive profiling of allelochemicals with liquid chromatography–mass spectrometry (LC-MS) determined 120, 113, 90, and 50 derivates of phenolic acids, flavonoids, and alkaloids, reported for the first time through this study, demonstrating significant allelopathic potential of the targeted plant fractions, which can be explored further to develop a sustainable bio-herbicidal formulation.
... Just like other pesticides, the continued use of synthetic herbicides in agricultural and non-agricultural plants poses health risks and pollution [71]. Because of this problem, several plants have been investigated for their allelopathic characteristics that either stimulate or inhibit the growth of their neighboring plant species as these allelochemicals play an important role in the ecological function of the plant [72,73]. Among these allelochemicals, terpenoids, phenolics, and nitrogen-containing compounds such as alkaloids were reported as the plant defense systems against external factors and plant growth inhibitors [73,74]. ...
Pesticidal poisoning has been relatively uncontrolled since the 1960s. The rate of intentional and unintentional pesticide
poisoning cases reflects how extensively the community and local agriculture uses these agents. Pesticides are mostly
synthetic and toxic substances. Its health risks outweigh the benefits it possesses; thus, it is necessary to look for a natural
and less toxic alternative. Pittosporum moluccanum was traditionally used as an herbal pesticide; however, no scientific
findings support this claim. Thus, we aim to substantiate the plant’s pesticidal effect. Briefly, the ethanolic extracts of the
leaves, fruits, and barks were obtained and chemically profiled using TLC principles. Then, their toxicity was screened using
brine shrimp lethality assay and MTT cytotoxicity assay. The pesticidal activity of the extracts was determined using
phototoxicity assay against barnyard seeds and immersion screening method against golden apple snails comparing their
activities against glyphosate and metaldehyde as positive controls and, water and DMSO as growth controls. Chemically,
the extracts contain semipolar and UV-active secondary metabolites that belong to the alkaloids, flavonoids, phenolics, and
tannins group of compounds. Moreover, toxicity profiling suggests an LC50 of 0.098 mg/mL for leaves extract while 3.125
mg/mL for bark and fruit extracts; and, CC50 of 0.39 ug/mL for fruit extract while 0.2 ug/mL for both leaves and bark
extracts. For pesticidal activity, seed germination inhibition of 85.56% (±1.20SD), 87.78% (±1.22SD), and 91.11%
(±1.28SD) was observed on the leaves, fruits, and bark, respectively, while the positive control (1 µg/mL glyphosate) only
exhibited 84.44% ± 1.57 SD. Immersion assay results suggest that the plant extracts exhibit a concentration-dependent
molluscicidal activity against the snails and a 71.11% (±1.33SD) activity for 6 µg/mL metaldehyde (positive control). Our
findings suggest that P. molucannum plant contains compounds that exhibit pesticidal activities against snails and weeds
which are the most common pests in agricultural lands.
... Wheat residues can reduce weed emergence, weed density, and weed yield due to allelopathic chemical effects (Elliott et al., 1978), toxic microbial products (Aslam et al., 2017;Jilani et al., 2008;Zuo et al., 2014), and pH changes in the soil (Kimber, 1973). Compared to other crops, wheat has a high potential for allelopathic weed control (Farooq et al., 2020; Table 1). ...
Global wheat production has remained stable in the last 20 years, benefiting from
increased grain yields despite decline in harvested wheat area. Here, we conducted
a comprehensive review of ca. 300 peer-reviewed studies worldwide to outline benefits of adding wheat to simple crop rotations (i.e., one to three rotational crops). We highlight the wheat’s versatility for tactical in-season crop management (e.g., flexible sowing dates, crop type [winter vs spring], and nitrogen fertility) and strategic cropping system management (e.g., grazing and double-cropping) and provide evidence supporting the positive impact of wheat on the grain yield and yield stability of other rotational crops. The inclusion of wheat in simple cropping systems enhances agroecosystem diversity and improves resilience to biotic and abiotic stresses. The high carbon-to-nitrogen ratio (C:N) residue of wheat offers benefits and drawbacks on soil quality attributes, weed control, and climate change mitigation potential. The introduction of wheat to simple crop rotations can (i) interrupt pest population cycles by serving as a break crop; (ii) decrease N application requirements, thus reducing N losses, greenhouse gas emissions, soil acidification, and production costs; (iii) improve soil health and carbon sequestration; (iv) increase resource use-efficiency of the cropping system; (v) foment fauna population; and (vi) decrease variability in economic returns. This review highlights that wheat offers unique opportunities to increase diversification and foster more sustainable and resilient agroecosystems that will feed a growing global population while acting as a net carbon sink, helping to mitigate drivers of climate change.
... Allelopathy is the effect of a plant on other plants through the release of chemical compounds into the environment. In general, allelopathy is interspecific where the chemicals released by one species are phytotoxic to another species and are termed heterotoxic (Jilani et al. 2008;Miller 1996). Allelochemicals enter the environment by decomposition, volatilization, or root exudation and may move through the soil by leaching (Zimdahl 2018). ...
The exotic ornamental tree Senna spectabilis (DC.) H. S. Irwin and Barneby has invaded various Protected Areas of the Nilgiri Biosphere Reserve including the Wayanad Wildlife Sanctuary in India creating a significant threat to biodiversity. This study examined the allelopathic potential and heterotoxicity of invasive S. spectabilis leaf extract by bioassay under laboratory conditions and identified its allelochemicals using HRLC-ESI–MS (QTOF) analysis. The bioassay experiment with test plant species including Vigna radiata (mung bean), Cicer arietinum (chickpea), and Amaranthus cruentus (red amaranth) was conducted in the laboratory and the methanolic leaf extract found to exhibit the greatest inhibitory activity. The percentage of inhibition of plumule growth by methanolic leaf extract on V. radiata, C. arietinum, and A. cruentus were 82%, 86%, and 99%, respectively. Phenol and proline content were significantly increased in germinated seedlings treated with even a quarter strength of leaf extract. Further by HR-LCMS analysis fifteen important allelochemicals were identified including phenolic compounds, flavonoids, anthraquinone, benzoic acid derivatives, and cinnamic acids. A soil sterilization experiment was used to examine the role of soil microbes in the phytotoxicity of leaf leachate. No significant variations exhibited in the phytotoxicity. The full strength of leaf leachate inhibited the shoot length of B. bambos by 52% in the sterile and 48% in the non-sterile soil, whereas it was 74 and 68%, respectively, in V. radiata. Further studies in the process of allelochemical release and their mode of action may confer a more lucid knowledge concerning the invasion mechanisms of S. spectabilis through allelopathy, guiding to practical management strategy.
... The allelochemicals in an oat variety which had shown toxicity became stimulatory within 4 days and inhibitory 14 days later. From the result of this experiment, it can therefore be deduced that at the early stage of the experiment, C. odorata inhibited the germination of C. lanatus seeds because it was phytotoxic at that initial period but as time progressed, the phytotoxic effect of the allelopathic material wore off or it simply changed form and became a stimulant to the elongation of the seedlings [24], [17]. ...
This study investigated Chromolaena odorata's allelopathic influence on Citrillus lanatus and Cucumis sativus seedling emergence and growth. We used a completely randomized design with three treatments (T1: 5g, T2: 10g, T3: 15g) in 300g of soil, each with four replicates. We assessed seedling emergence percentage (SE%), seedling emergence index (SEI), time spread of emergence (TSE), allelopathic response index (ARI), seedling lengths (SL), and dry weights (DW), analyzing data with ANOVA and Tukey's HSD test. C. lanatus SE% (97.5%, 97.5%, 92.5%, 72.5%) and SEI (15.9, 14.9, 13.6, 10.9) were not significantly reduced. SE% (90%, 50%, 55%, 30%) and SEI (13.2, 9.5, 5.5, 2.3) of C. sativus decreased non-significantly. TSE values in the treatment plots were all higher than the control while ARI values were negative indicating delayed and inhibited emergence in both crops. Contrary to the inhibitory effect of T1, T2 and T3 on SL of C. sativus, T1 and T2 stimulated SL in C. lanatus while T3 inhibited growth. DWs did not reduce significantly but was concentration-dependent. This study underscores the variable allelopathic effects that C. odorata possesses which is influenced by plant species, allelopathic material concentration, and crop growth phase. Consequently, C. odorata can be strategically incorporated into crop rotation and weed control practices.
... Allelopathic substances were excreted by plant roots and may enter into soil system by means of the breakdown of plant remains, and the permeation of rain, dew or snow water (Jilani et al., 2008). Continuous long-term farming has resulted in the accumulation and diversity of allelochemicals in the soil, which has aggravated the obstacle of continuous cropping of Chinese herbs Korai et al., 2018). ...
... This idea of degradation, as reported by (Otusanya et al. 2015) and recast as "bio-transformation" in some texts, shows that it is possible that the allelochemicals in the plant extract or foliage that would have been phytotoxic to the target plant was "bio-transformed" by certain soil-borne factors (especially microbes) to new allelochemicals with growth stimulatory effect. This is a possibility that has been reported by Jilani et al. (2008). This, therefore, necessitates the use of chemical profiling methodologies to determine the chemical changes in the soil due to the application of the aqueous fresh shoot extract of C. odorata, towards a better understanding of the mechanism of the Janus-faced allelopathy of C. odorata. ...
This study investigated the allelopathic effect of Chromolaena odorata foliage used as soil amendments on the leaf area, plant height, number of leaves, plant biomass and total chlorophyll content of Solanum lycopersicum, Mucuna pruriens, Abelmuschus esculentus and Citrullus lanatus. Seeds of the test crops were planted in pots amended with 0%w/w, 1.9%w/w, 3.8%w/w, 5.7%w/w and 7.7%w/w of foliage of C. odorata and parameters as leaf area, plant height, number of leaves, plant biomass and total chlorophyll content were measured. The data collated were analysed using analysis of variance and the means separated using Tukey's HSD. The leaf area, plant height, number of leaves and plant biomass showed a seemingly concentration-dependent, statistically significant increase in C. lanatus, S. lycopersicum and A. esculentus for all treatments, when compared to the 0%w/w treatment; and, although showing a visual and graphical increase for, M. pruriens, the increase in leaf area, plant height, number of leaves and plant biomass of M. pruriens were not statistically significant at 5% level of probability. The total chlorophyll content of all the plants studied showed concentration-dependent, statistically significant increments at 5% levels of probability, when compared to their respective 0%w/w treatments. The increase in the leaf area, plant height, number of leaves, plant biomass and total chlorophyll content of C. lanatus, S. lycopersicum, A. esculentus and M. pruriens due to the soil amendment with different amounts of C. odorata foliage is attributed to the possible effect of the allelochemicals in the leaves, which, although having a negative inhibitory effect on germination, had possibly undergone a bio-transformation to become stimulatory. Again, the foliar amendments increased the organic matter content of the soil, and thus, in synergy with the bio-transformed allelochemicals, serve as a bio-fertilizer to improve the growth of the test crops. Owing to the possible inhibitory effect of C. odorata foliage on the germination of these same test crops, it is therefore recommended that the foliage of C. odorata should only be used as organic manure or bio-fertilizer only at the post-germination stage of the test crops, not at the pre-germination stage.
... Thus allelochemicals, when applied to the crops in lower amounts, can result in an economical, efficient, and professional method to improve crop productivity and to endorse the growth and development of crop species. There is variability in the concentration and activity of allelochemicals in the varied parts of the same plant, and the activity also varies along the growing seasons (Qasem and Foy 2001;Kato-Noguchi 2002;Jilani et al. 2008;Uniyal and Chhetri 2010;Gatti et al. 2010). ...
Population increase, poverty, environmental
degradation and the use of synthetic herbicides are interdependent and closely linked and hence influence global food
safety and stability of world agriculture. On the one hand,
varied weeds, insects, and other pests have caused a tremendous loss in agricultural crop productivity annually. On
the other hand, the use of synthetic insecticides, herbicides,
fungicides and other pesticides significantly disturbed the
ecology of biotic communities in agricultural and natural
ecosystems. Eventually, it destroyed the ecological balance in food chains. Interestingly, natural products released
by the plants (allelochemicals) are secondary metabolites
involved in ecological interactions and could be an important source of alternative agrochemicals. Mainly released by
the plants as an outcome of acquaintances with other plants
in their vicinity, these allelochemicals can also be used as
eco-friendly substitutes for synthetic herbicides and other
pesticides. Despite these facts, agrochemicals are either preferred over allelochemicals or the latter are not known in the
the direction of their use in achieving sustainability in agriculture. Given this, considering recent reports, this paper aims
to: (1) emphasize allelochemicals; (2) overview the major
biochemistry of allelochemicals; (3) critically discuss the
role of allelopathy (and underlying major mechanisms) in
the management of noxious weeds, insect pests, and major plant pathogens; and (4) enlighten the significant aspects so
far not or least explored in the current context.
... Considerations for the rhizosphere include microbes, nearby plants, organic and inorganic materials, pH, consistency, and moisture content [31]. Prior to reaching the target species, these conditions may have an impact on the physiochemical nature of allelopathins in the rhizosphere and consequently their phytotoxic activity [32][33][34]. The required concentration of potent allelopathins must therefore be examined under edaphic scenario in order to precisely determine their phytotoxicity [35]. ...
Chemical herbicides are the primary weed management tool, although several incidences of herbicide resistance have emerged, causing serious threat to agricultural sustainability. Plant derived phenolic acids with herbicidal potential provide organic and eco-friendly substitute to such harmful chemicals. In present study, phytotoxicity of two phenolic compounds, ferulic acid (FA) and gallic acid (GA), was evaluated in vitro and in vivo against three prevalent herbicide-resistant weed species (Sinapis arvensis, Lolium multiflorum and Parthenium hysterophorus). FA and GA not only suppressed the weed germination (80 to 60% respectively), but also negatively affected biochemical and photosynthetic pathway of weeds. In addition to significantly lowering the total protein and chlorophyll contents of the targeted weed species, the application of FA and GA treatments increased levels of antioxidant enzymes and lipid peroxidation. Photosynthetic gene (psbA) expression was downregulated (10 to 30 folds) post 48 h of phenolic application. In silico analysis for receptor identification of FA and GA in psbA protein (D1) showed histidine (his-198) and threonine (thr-286) as novel receptors of FA and GA. These two receptors differ from the D1 amino acid receptors which have previously been identified (serine-264 and histidine-215) in response to PSII inhibitor herbicides. Based on its toxicity responses, structural analogs of FA were also designed. Four out of twelve analogs (0.25 mM) significantly inhibited weed germination (30 to 40%) while enhancing their oxidative stress. These results are unique which provide fundamental evidence of phytotoxicity of FA and GA and their analogs to develop cutting-edge plant based bio-herbicides formulation in future.
... It is evident that not all bioactive metabolic compounds possess the allelopathic effect on surrounding organisms (Neori et al., 2000). Among all the pathways, root exudates are the most prominent source of release of allelochemicals into the rhizosphere (Jilani et al., 2008). The mechanism of release of allelochemicals from the roots of the donor plant as exudate is described vividly in Fig. 2. ...
Plant allelopathy is a response to external stimuli by releasing secondary metabolites. It can be an effective sustainable strategy for weed control. Roots are the main point of release of allelochemicals. This phenomenon has the potential to facilitate environmentally cleaner weed control and avoid the concerns associated with the misuse of agro-chemicals for pest and weed management. The review comprehensively elaborates the mechanisms involving the release of allelochemicals by plants and the factors affecting its transport from a donor plant to a receiver. Although allelochemicals are produced by the entire plant, root exudation is the primary source of release of these chemicals into the soil environment. The study attempts to lucidly explain the physiology behind phytotoxic effects imparted by allelochemicals on target plants. We have discussed the various direct and indirect effect of allelochemicals on plant physiology and morphology. The review sheds light on the phytotoxic variation caused due to variable residue decomposition rates under changing climatic conditions. The various crop-weed, weed-crop and weed-weed allelopathic interactions and their possible response mechanisms have been briefly elaborated with reference to earlier works. We have shown the potential of integrating allelopathy and agronomic management practices for sustainable and environmentally safe weed management. The mechanistic insight of interferences caused by environmental factors on the bioavailability of allelochemicals is essential to develop an environmentally sound method of curbing the weed menace in agro-ecosystems. The studies on transport processes involving the release of allelochemicals from plants need more attention so as to exploit this knowledge in regulating the output of these compounds at a cellular level.
... However, the allelopathic effects of a plant specie depends upon the quality and bioactive quantity of allelochemicals and the intensity of the effects may vary with specificity and efflux-matrix-influx compatibility (17,29). In addition, certain allelochemicals are more potent and can cause greater inhibitory effects (8). Therefore, differential production of allelochemicals by fruits, branches, and leaves might have been responsible for the variable impact on the growth parameters. ...
The present study was conducted to investigate the allelopathic effects of abscised plant parts of Terminalia arjuna on germination, growth, and physio-biochemical processes of Triticum aestivum L. Different doses of plant material obtained from fruits (F100 and F50), branches (B100 and B50), leaves (L100 and L50), and the mixture of all plant parts (A100) were applied to the seedbeds of two varieties of T. aestivum, DPW-62150 and DBW-17. It was observed that both the varieties differed in the intensity of response towards the treatments measured in terms of seed germination, shoot length, root length, dry weight, vigour index, tolerance index, total chlorophyll, nitrogen and organic carbon. The mixture of all the plant parts of T. arjuna stimulated most of the studied parameters and wheat variety DBW-17 performed better as compared to DPW-62150. A total of 49 allelochemicals were identified in the GC-MS analysis, of which 28, 28, and 30 were present in the fruit, branch and leaf powder, respectively. It can be inferred from the study that T. aestivum, particularly variety DBW-17, can be successfully intercropped with T. arjuna. However, further field studies should be undertaken on a wider scale to validate the results of this study.
... Х орошо известно явление накопления в почвах аллелотоксинов, которые оказывают сильное негативное влияние на почвенное плодородие и урожайность сельскохозяйственных растений [1][2][3][4][5][6][7][8][9][10][11]. ...
Sorption-stimulating preparation has been developed, and its effect on allelotoxicity reduction of soils and soil-like substrates has been studied. Calcium bentonite and potassium humate with the addition of brewer’s yeast autolysate and polyethylene glycol are the base of the preparation. The preparation reduces the soil allelotoxins for plants due to sorption. Optimal concentrations of composition components of the developed preparation were determined. The profitability of the preparation application when introducing it into the soil substrates of greenhouses was justified.
... Once produced and released, plant allelochemicals experience physico-chemical and microbial transformations resulting in alterations in phytotoxicity (Inderjit, 2005;Jilani et al., 2008;Mwendwa et al., 2021), resulting in production of novel allelochemicals by associated microorganisms. Allelochemical transforming non-pathogenic bacteria can directly impact crop growth by inducing toxicity in the crop plant or indirectly by suppressing a necessary symbiont (Barazani and Friedman, 2001). ...
Allelopathic activity of wheat (Triticum aestivum L.) has previously been associated with the production of phenolic acids and flavonoids (PAF), benzoxazinones (BXZs) and phenoxazinones (PXZs). The biosynthesis of BXZs is closely regulated during cereal growth, with accumulation highest in young tissues with variation associated with genotype and environmental conditions. This review is focused on BXZ metabolites and their impact on germination, seedling growth and physiological, biochemical, transcriptional and proteome traits of surrounding plants and weeds. The major pathways employed by plants for benzoxazinoid detoxification involve hydroxylation and glucosylation and polymerisation of intermediates in these pathways. Allelochemicals from various wheat genotypes have been shown to inhibit the growth of selected weed species, including Bromus japonicus, Chenopodium album, Portulaca oleracea, Avena fatua and Lolium rigidum. Wheat allelopathy is potentially exploited from the standpoint of crop mulches, incorporation of crop residues, tissue disruption, intercropping with allelopathic cultivars and application of aqueous wheat extracts. BXZs have been shown to suppress the growth and development of certain agricultural pests, including insects, fungal pathogens, and weeds. Many native plants, fungi and insect herbivores inherently possess varying tolerance levels towards BXZs. However, other BXZ- susceptible species are adversely impacted by elevated BXZ levels in crop plants. Thus, considerations for the selection and breeding of wheat genotypes possessing enhanced defensive ability via elevated BXZ contents are discussed. Here, these objectives are reconsidered with a focus on co-evolutionary aspects and their potential impacts on biodiversity in the agroecosystems under study. For future breeding efforts to be successful, it is important to take such potential adverse environmental impacts into account, in combination with an increased focus on enhancing beneficial allelopathic effects within agricultural systems.
... Microorganisms influence these allelocompounds with negative and positive consequences (Lou et al. 2016). Microbes can deactivate the plant toxins that are soluble in water or degrade toxic compounds to decrease the allelopathic effects, thereby exhibiting a negative role in allelopathy (Jilan et al. 2008). Conversely, microbes can also liberate insoluble phytotoxins and convert the non-toxic compounds to phytotoxins, consequently indicating a synergism with allelochemicals (Lou et al. 2016). ...
There is a need to increase food productivity due to the ever-increasing human population worldwide. Modern agriculture practices including extensive application of synthetic chemicals for crop production and protection have led to decreased soil fertility and other hazards to the environment. However, the exploration of a wide range of microorganisms inhabiting the soil can improve crop growth and productivity. The plant–microbe interaction forms an important network in agriculture. The beneficial soil microorganisms including arbuscular mycorrhizal (AM) fungi, plant growth-promoting rhizobacteria (PGPR), nutrient-solubilizing bacteria, cyanobacteria, some groups of protozoa, and nematodes have a crucial role in plant’s growth promotion, nutrient acquisition, imparting tolerance against different environmental stresses, and improving soil structure. Some of the important mechanisms involved in soil microbe-mediated processes are improved plant growth including phytohormone production, nutrient solubilization, and suppression of phytopathogens. The development of bioinoculants using efficient microbial consortiums can reduce the dependence on chemical fertilizers and could enhance crop productivity even under stressful conditions in an eco-friendly and cost-effective manner. In addition, soil health is strongly related to sustainable agriculture as the diversity and activity of soil microorganisms form a vital part of soil health. Therefore, in this chapter, we highlight the diversity of beneficial microbes in the pedosphere and their role in sustainable agriculture production.
... As functional ecology has provided a more mechanistic view of plant community organization, intraspecific variation has also become a critical component (Violle et al. 2012;Hahn and Maron 2016). Intraspecific variation in plant chemistry can impact the quality of anti-predator defenses (Glassmire et al. 2016;Benedek et al. 2019), responses to interspecific competition (Jilani et al. 2008), as well as resistance to pathogens and parasites (Biere et al. 2004;Shikano et al. 2017), linking above-and belowground processes (Van Der Putten et al. 2001;Bezemer and Van Dam 2005). Similarly, variation in plant chemical composition may result in changes to the composition of soil microbial communities (Lankau 2010;Benedek et al. 2019), with microbial biomass dependant on chemical and litter inputs and the responses of individual microbes to them (Kong et al. 2008). ...
Plant–soil microbe interactions are a key determinant of plant community composition and structure, with each plant species generating a unique soil microbiota. However, the degree of intraspecific variation in plant–soil microbe interactions in controlling plant performance has been much less investigated. We examined the strength of plant–soil microbe interactions across Solidago altissima and Schizachyrium scoparium seedlings grown in soils cultured by 24 genotypes of S. altissima in a greenhouse setting to determine the level of variation within these two target species. We also quantified leaf chemical variation across S. altissima genotypes using HPLC characterization of foliar constituents as a potential driver of below-ground processes. The impacts of soil microbe-mediated effects of genotypes ranged from negative to positive for both target species. Target species responses to the 24 soil microbial communities were positively correlated, although the strength of plant–soil microbe interactions was related to foliar chemistry for S. scoparium, but not for S. altissima. The magnitude of impacts in soils pooled from all 24 S. altissima genotypes was more negative than the average impact of genotypes tested individually, suggesting that this methodology cannot be used to assess ‘average’ effects. Our results strongly argue that intraspecific variation in plant–soil microbe interactions may be a quite large source of variation in systems dominated by clonal plants. Furthermore, simple inocula pooling obscured this variation and resulted in a marked bias toward the more antagonistic components of the soil microbial community.
... It is indispensable to investigate the abiotic (physical and chemical) and biotic (microbial) soil barriers in environment that can limit the chemical or phytotoxic compound concentrations available to cause injury to the plants (Ohno, 2001;Salhi et al. 2013). In order to inhibit plant or weed growth, allelochemical or secondary metabolites must accumulate and persist at certain phytotoxic levels in the rhizosphere soil (Jilani et al., 2008). Although 2,4-DTBP has been demonstrated strong phytotoxic effect on various plants and weeds in previous findings, information on its preemergence activity in the soil is still scanty. ...
Although 2,4-di-tert-butylphenol (2,4-DTBP) has demonstrated strong phytotoxic effect on various weedy plants in previous findings, research on its pre-emergence herbicidal activity in the soil is still scanty. The aim of this study was to investigate the effects of two soil types on pre-emergence herbicidal activity and persistence of 2,4-DTBP. The bioassay was carried out in a growth chamber where goosegrass [Eleusine indica (L.) Gaertn.] seeds were sown in different rates of 2,4-DTBP in two soil series under sterilized and non-sterilized soil conditions. Bioassays of each treatment were conducted in four replicates and arranged in completely randomized design. 2,4-DTBP exhibited potent pre-emergence activity as a root inhibitor where it completely inhibited (100% inhibition) of the root growth of E. indica in sandy loam soil at an application rate of 6.14 kg ai/ha. 2,4-DTBP was rapidly detoxified in silt loam soil as a result of high microbial activity where it completely lost its phytotoxicity by giving 100% emergence within 10 weeks even it was applied at an application as high as 20.4 kg ai/ha. However, 2,4-DTBP remained highly phytotoxic in sandy loam soil where it reduced the root and shoot growth by 47 and 36%, respectively, throughout 10 weeks duration of the investigation. The presence of microbes in non-sterilized soil further suggest that soil microbes may modify the chemical structure of the 2,4-DTBP, which in turn decreased its toxicity. The high level of pre-emergence herbicidal activity in conjunction with its biodegradation in silt loam soil imply that 2,4-DTBP may have potential for development as a natural-soil applied herbicide
... Therefore, even though it can be demonstrated that these alkaloids are released into the soil matrix, either via leaching, litter decomposition or root exudation, still, like other allelochemicals, the fate of these alkaloids depends greatly on the environment. Once they enter the soil, these chemicals are exposed to various physicochemical and biological processes which might trigger degradations or chemical reactions that lead to the production of novel compounds with different biological activities [38]. ...
Sophora alopecuroides is known to produce relatively large amounts of alkaloids; however, their ecological consequences remain unclear. In this study, we evaluated the allelopathic potential of the main alkaloids, including aloperine, matrine, oxymatrine, oxysophocarpine, sophocarpine, sophoridine, as well as their mixture both in distilled H2O and in the soil matrix. Our results revealed that all the alkaloids possessed inhibitory activity on four receiver species, i.e., Amaranthus retroflexus, Medicago sativa, Lolium perenne and Setaria viridis. The strength of the phytotoxicity of the alkaloids was in the following order: sophocarpine > aloperine > mixture > sophoridine > matrine > oxysophocarpine > oxymatrine (in Petri dish assays), and matrine > mixture > sophocarpine > oxymatrine > oxysophocarpine > sophoridine > aloperine (in pot experiments). In addition, the mixture of the alkaloids was found to significantly increase the IAA content, MDA content and POD activity of M. sativa seedlings, whereas CTK content, ABA content, SOD activity and CAT activity of M. sativa seedlings decreased markedly. Our results suggest S. alopecuroides might produce allelopathic alkaloids to improve its competitiveness and thus facilitate the establishment of its dominance; the potential value of these alkaloids as environmentally friendly herbicides is also discussed.
... Indeed, soil microorganisms have been reported to outcompete plants for nitrogen (N) and phosphorus (P), immobilizing these nutrients in microbial biomass, which becomes unavailable for plant uptake, at least in the short-term (Čapek et al. 2018). Also, the negative effects of microbes on plant growth can be related to the production of phytotoxic compounds that hinder plant development (Jilani et al. 2008). Therefore, to understand the mechanisms by which litter input affects plant growth, it is also important to evaluate the effects of litter input on soil microbiota activity and biomass. ...
PurposePlant-soil feedbacks are important drivers of ecosystem dynamics and have been hypothesized to affect woody encroachment in savannas. Woody encroachment is expected to increases savanna soil fertility through deposition of organic matter, favoring further establishment of woody individuals. In this context, we tested if litter input promotes forest seedling growth in dystrophic savanna soils, and if this was accompanied by an increase in microbial activity.Methods
In a glasshouse experiment, we planted woody seedlings of three forest species in savanna soils either mixed or not (control) with litter from closely related savanna or forest species (10 species). We evaluated the growth of the woody seedlings as well as the response of the soil microbiota activity and biomass to litter addition.ResultsLitter addition had either no effect or negative effects on seedling growth, and different seedling species responded differently to litter addition. However, we did find microbial activity to increase in response to litter addition, especially through the input of litter rich in phosphorus (P) and carbon (C).Conclusions
Our results indicate that litter input does not favor woody seedlings growth in savanna soil. Instead, litter input showed a potential to hinder seedling growth, especially of fast-growing species. Furthermore, litter input consistently increased soil microbiota activity, mainly through the input of P and C, highlighting the importance of energy and P in the nutrient dynamics of Cerrado. Thus, our results did not support the hypothesis that litter deposition triggers a positive feedback with woody encroachment via increased seedling growth.
... Studies demonstrate that sawdust decomposition and, consequently, the release of secondary metabolites are key factors in allelopathic processes, mainly affecting seedling growth and survival (Bonanomi et al., 2006;Huang et al., 2019). The allelopathic effect of the decomposition of plant residues has been attributed mainly to the fact that the chemical compounds released from the sawdust can persist in the soil even after the senescence and decomposition of the plant, which can cause effects on the growth or germination of neighboring and nearby plants generations (Jilani et al., 2008;Bonanomi et al., 2011). ...
Azadirachta indica have allelopathic potential, attributed to the presence of allelochemicals capable of altering plant diversity in surrounding areas. This work aimed to evaluate if the decomposed leaves of A. indica can affect the germination and growth of Myracrodruon urundeuva. A. indica leaves were collected at the end of senescence and mixed with soil in different concentrations and decomposed for 90 and 180 days. Through phytochemical analysis, it was found the presence of diterpenes and triterpenes, such as margocinolide, epoxyazadiradione and salimuzzalin. Leaf decomposition negatively affected germinability, emergence speed and the germination synchrony index of M. urundeuva, especially during the first decomposition period. The residues of the leaves of A. indica also negatively affected the length of the young plants of M. urundeuva, since the lengths of the stem and root were reduced, and the treatment of lower concentration a reduction in root length was observed only in the first decomposition period (T1). Leaf residues in the first decomposition time also negatively influenced the total biomass of M. urundeuva, in all treatments evaluated. The decomposition were also able to change the amount of photosynthetic pigments in the first decomposition period, since the total chlorophyll content had a reduction from the average value of 3.23 to 2.40 g/kg, corresponding to a 25.71 inhibition. The observed results suggest that the compounds present in the litter of A. indica have an allelopathic action, being necessary to limit the use of the former in areas that need ecological restoration and in preserved natural environments.
... It could also be that in nature many allelopathic effects are indirect effects mediated by chemical inhibition of mutualistic microbes (e.g. Stinson et al. 2006) or that plant compounds are converted into more potent phytotoxic compounds by microbes (Jilani et al. 2008). By doing the germination experiment under almost sterile conditions, we excluded these possibilities in our experiment. ...
The novel-weapons and homeland-security hypotheses are based on the idea that aliens and natives are not adapted to each other's allelochemicals as they did not co-evolve. However, as only a few studies have tested this, it remains unclear how important co-evolutionary history is in determining the strength of allelopathic interactions between aliens and natives. Here, we tested for potential pairwise allelopathic effects on each other of five alien and five native herbaceous species in China. We did a germination experiment and a competition experiment. In the germination experiment, we tested whether aque-ous extracts of the ten study species had allelopathic effects on each other's seed germination. In the competition experiment, we tested whether the alien and native species differed in their competitive effects and responses, and whether these were changed by the presence of activated carbon-a presumed allelopathy neutralizer-in the soil. Plant extracts had negative allelopathic effects on seed germination. This was particularly the case for extracts from the native species. Moreover, aqueous extracts had slightly stronger negative effects on germination of the aliens than on germination of the natives. In the competition experiment, on the other hand, the natives suffered more from competition than the alien species did, but we could not relate this to allelopathy. Alien plants had negative competitive and allelopathic effects on native plants, but the reverse was also true. These alien-native interactions, however, were not consistently stronger or weaker than native-native or alien-alien interactions.
... Häufig wird die Walnuss als Beispiel für Allelopathie genannt, da Blätter und andere Organe Juglon enthalten, welches beispielsweise über den Laubfall auf den Boden gelangt und sich dort anreichern und phytotoxisch wirken kann (Scott & Sullivan, 2007;Jilani et al., 2008;Wang et al., 2014). Widersprochen wird dieser Darstellung jedoch von verschiedenen Autoren, nach welchen Juglon sich nicht in phytotoxischen Mengen im Boden anreichern könne, da es von Bodenbakterien oder benachbarten Wurzeln zügig abgebaut oder aufgenommen würde. ...
Basierend auf aktuellen wissenschaftlichen Veröffentlichungen bieten silvopastorale Agroforstsysteme (SPS) eine Vielzahl von Möglichkeiten, landwirtschaftliches Handeln mit Klima- und Artenschutz zu vereinen und zudem Flächen- und Tierproduktivität sowie Tierwohl zu steigern. Gleichzeitig wird die Produktpalette eines Betriebes erweitert und damit das Einkommen diversifiziert. SPS sind gekennzeichnet durch hohe biologische Diversität, zeitliche, räumliche und funktionale Heterogenität und gezielte Integration der Komponenten in ein Gesamtsystem, welches intensiver Betreuung bedarf. Weiterhin sind Tiere und perennierende Pflanzen dominante Elemente in einer dem Standort angepassten Landnutzung und sollen stets mehrere Funktionen erfüllen. Störungen bspw. in Form von Wetterereignissen oder anthropogenen Eingriffen stellen eine wichtige Determinante dar. Silvopastorale Systeme werden mit Blick auf mehrere Jahrzehnte sowie standortbedingte und betriebliche Herausforderungen und Ziele entwickelt, weshalb der Artenwahl der Gehölze eine große Bedeutung zukommt.
Im Rahmen der vorliegenden Bachelorarbeit wird die Artenwahl von Gehölzen für ein multifunktionales, silvopastorales Agroforstsystem in Deutschland anhand eines Fallbeispiels durchgeführt. Nach Analyse von Standort, betrieblichen Zielsetzungen und Rahmenbedingungen wurde dazu eine Liste mit geeignet erscheinenden Gattungen und Arten erstellt und nach Literaturauswertung und wiederholtem Abgleich mit den gesteckten Zielen auf fünf Arten reduziert.
Für ein mit Rindern beweidetes System im Grafschafter Lösshügelland, welches in einen kleinbäuerlichen Betrieb mit Direktvermarktung integriert werden soll, wurde anhand dieser Verfahrensweise folgende Auswahl getroffen: Salix sp., Corylus avellana, Morus alba, Robinia pseudoacacia und Juglans regia. Diese Gehölze erfüllen jeweils verschiedene Funktionen und ermöglichen die Zusammenstellung zu einem System, welches in seiner Gesamtheit, die eingangs genannten Eigenschaften aufweist und den Zielsetzungen entspricht. Hierdurch können Tierfutter, Fruchtproduktion, Holzproduktion und positive Auswirkungen auf die biotische und abiotische Umwelt realisiert werden. Zudem bezieht das erstellte SPS aktuelle wissenschaftliche Ergebnisse mit ein, wie sich die Landwirtschaft an aktuelle Herausforderungen wie den Klimawandel anpassen könnte.
Im Rahmen dieser Arbeit werden die Merkmale und Potenziale der Arten genauer beleuchtet, diskutiert und zusammengetragen, um dem Bewirtschaftenden der Beispielfläche eine Übersicht zu gewähren und schließlich die Bewirtschaftung des Systems zu vereinfachen. Die entsprechende Gestaltung in Anlehnung an das Keyline Design wird skizzenhaft dargestellt.
Das entworfene SPS zeigt nach Auswertung der wissenschaftlichen Literatur deutliches Potenzial, landwirtschaftliches Handeln im Einklang mit Natur- und Klimaschutz zu ermöglichen, indem auf aktuelle Herausforderungen mit dem zukunftsorientierten Design resilienter, multifunktionaler, silvopastoraler Systeme geantwortet wird. Trotz des Potenzials ist die Zahl der SPS und die der wissenschaftlichen Arbeiten zu SPS in Deutschland noch gering und es bedarf hier weiterer Erfahrungswerte und Hilfestellungen auf politischer und wissenschaftlicher Ebene.
One of the most serious issues is biotic stress in plants produced by insect pests, which results in production losses. Synthetic pesticides continue to play an important role in crop protection. Yet, the environmental consequences and health risks caused by excessive or improper use of synthetic pesticides compelled authorities to ban some dangerous ones. As a result, there is an urgent need for unique and alternative insect pest management strategies. Allelopathy is a naturally occurring ecological phenomenon of organism interaction that can be used to manage weeds, insect pests, and illnesses in field crops. Allelopathy can be utilized in field crops after rotation, using cover crops, mulching, crop smothering, and plant extracts for natural pest management. Allelochemicals in soil are adsorbed on soil solids and decomposed during soil movement by chemical and biological reactions. Its behavior is influenced by soil characteristics such as soil texture, organic and inorganic matter, moisture, and organisms, all of which have an impact on phytotoxic activity in soil. Although allelochemicals are produced throughout the plant, root exudation is the principal source of chemical release into the soil environment. Therefore, this review will focus on the role of insect-pest management, factors affecting production and release of allelochemicals, their activity and limitations in insect-pest management.
The allelopathic plant Rhus typhina (Rt) has a shallowly distributed root system with a high density of secretory canals, which may allow it to exhibit indirect allelopathic effects through the soil on an understory turf species in a plantation. However, how these effects occur is still not well understood. For this study, the soil from the root zone of Rt was extracted via distilled water, and extracts at different concentrations (25, 50, and 100 g L⁻¹) were used to treat six commonly planted turfgrass species, including Medicago sativa (Ms), Lolium perenne (Lp), Trifolium repens (Tr), Medicago falcata (Mf), Festuca arundinacea (Fa) and Coronilla varia (Cv), during a continuous germination–seedling culture experiment via the sand culture method. The germination, physiological, and growth indicators of the turfgrass seedlings were analyzed. The allelopathic effects of the soil extract at different concentrations on the six receivers were evaluated to provide a scientific basis for managing plantations with multilayer structures. The results indicated that, in general, the extracts of the soil from the root zone of Rt inhibited the germination and seedling growth performance characteristics of the mentioned turfgrasses; the inhibitory effects on Ms, Lp, and Mf increased with increasing concentrations of the Rt soil extracts, whereas those on Fa tended to decrease. In addition, the inhibitory effect on Tr obviously weakened at 50 g·L⁻¹ relative to that at 25 g·L⁻¹, whereas it became more obvious at 100 g·L⁻¹; however, it exhibited the opposite trend for Cv. Generally, Mf and Cv were more sensitive to Rt allelochemicals at relatively low concentrations, and these species should be avoided when planting in Rt plantations at low densities. In contrast, Lp and Tr were more sensitive than those at relatively high concentrations and should be avoided when planting in Rt plantations at high densities.
In Agricultural sector, with the change in environment and climates has affected the diverse ecosystem and microbial life present in the soil. Soil microbial communities have directly or indirectly impacted the proliferation of plant systems. These communities contribute uniquely to ecological balance of soil, due to presence of variety of organisms such as bacteria, archaea, protozoa, fungi, etc. These communities can directly impact plant growth and development by producing growth-promoting hormones, nutrient acquisition, and protection against pathogens. Various factors like Temperature, pH, organic matter, and nutrient availability effects the action and mechanism of these microbial communities. Understanding their dynamics and interactions with plants is crucial for sustainable agriculture, nutrient cycling and ecosystem stability. In this chapter, we explore the role of soil microorganisms in plant proliferation, interactions between plants and soil microbial community, management strategies for soil microbial community, etc.
This textbook provides a comprehensive overview of the principles, methods and applications of chemical ecology, covering such topics as chemical signalling, predator–prey interactions, host plant selection and chemical defence. The book takes the reader through the historical development of the discipline to current state-of-the-art research, delving into recent findings on the role of chemical ecology in conservation and management and exploring how the field may contribute to future innovations in ecological science. A chapter is dedicated to the techniques that have been used in chemical ecology and some success stories.
Chemical Ecology: Insect-Plant Interactions is an important resource for advanced undergraduates and postgraduate researchers as well as practitioners in this interdisciplinary field. The book’s layout aligns with the curriculum of chemical-ecology-related disciplines, progressing from basic fundamental principles to a more advanced level. Those studying and researching in ecology, entomology, plant biology and biochemistry will find it invaluable as well as those practising in areas such as agriculture, forestry and pest management.
The allelopathy definition accepted by the International Allelopathy Society is any process or phenomenon via which organisms such as plants, microorganism, viruses, and fungi release specific metabolites, known as allelochemicals, into the environment that affect the growth and development of other surrounding plants, resulting in mutual inhibition or promotion of the organisms. Allelopathy in donor plants is either self-induced or induced by specific external biotic and abiotic factors. The external factors may determine the types and quantities of allelochemicals released into the environment by a donor plants. Biotic factors inducing allelopathy include plant competition, herbivory by animals and insects, and soil-borne pathogens. For example, competing plants produce allelochemicals in response to competing weeds. Plants may emit signaling chemicals from their roots to induce the production of protective metabolites against organisms, herbivores, or competitors. Additionally, herbivory is a selection pressure that triggers defensive measures in plants, such as the synthesis of allelochemicals in response to injury. Moreover, some leaves release volatile substances that help the plant to deter or attract herbivores or pests that attack leaves. Likewise, root compounds may be produced in response to soil-borne pathogens. Furthermore, some abiotic factors, including light, temperature, drought, CO2, and nutrient deficiency, can also induce plants to release allelochemicals. Therefore, it is pertinent to understand this natural phenomenon in plants and how external factors lead plants to exert allelopathy to compete, defend themselves, and survive in a challenging environment.
Understanding the response of microbial communities and their potential functions is essential for the long-term continuous-cropping agroecosystems. However, there are few studies on the interaction between soil physicochemical factors and microbial community dynamics in agroecosystems under long-term continuous-cropping conditions. We investigated the physicochemical properties, metabolites, and microbial diversity of rhizosphere soils in which tobacco was cropped continuously for 0, 5, and 20 years. The results showed that the bacterial diversity significantly increased and then decreased with the duration of continuous-cropping. In addition, the fungal diversity increased significantly, indicating that the change in fungi may shift the nutrient cycles of continuous-cropping karst agroecosystems. In this study, soil pH and the contents of available phosphorus (AP) and available nitrogen (AN) were the key environmental factors leading to changes in the structures and functions of microbial communities in continuous-cropping soil. The metabolites released by tobacco, such as palmitic acid, 3-hydroxypropionic acid, stearic acid, and hippuric acid, reduced soil pH.
Finding strategies to treat, dispose of and reuse organic wastes is of utmost need. Biological processes offer the possibility to transform them into safer end products with benefits for both agriculture and the environment. This is of particular interest for the winemaking industry given its increasing activity worldwide with the subsequent generation of a wide variety of waste streams. The purpose of this chapter is to evaluate the effectiveness of the vermicomposting process as a low-cost and environmentally safe solution for the treatment and valorization of raw and distilled grape marc, the major solid by-products derived from the winery and distillery industry. We give an overview of the performance of the vermicomposting trial together with an in-depth characterization of the respective vermicomposts by looking at a combination of physicochemical, biochemical and microbiological indicators.
Background
In the grass family, a disproportionate number of species have been designated as being invasive. Various growth traits have been proposed to explain the invasiveness of grasses; however, the possibility that allelopathy gives invasive grasses a competitive advantage has attracted relatively little attention. Recent research has isolated plant allelochemicals that are mostly specific to the grass family that can breakdown into relatively stable, toxic byproducts.
Methods
We conducted a meta-analysis of studies on grass allelopathy to test three prominent hypotheses from invasion biology and competition theory: (1) on native recipients, non-native grasses will have a significantly more negative effect compared to native grasses (Novel Weapons Hypothesis); (2) among native grasses, their effect on non-native recipients will be significantly more negative compared to their effect on native recipients (Biotic Resistance Hypothesis); and (3) allelopathic impacts will increase with phylogenetic distance (Phylogenetic Distance Hypothesis). From 23 studies, we gathered a dataset of 524 observed effect sizes (delta log response ratios) measuring the allelopathic impact of grasses on growth and germination of recipient species, and we used non-linear mixed-effects Bayesian modeling to test the hypotheses.
Results
We found support for the Novel Weapons Hypothesis: on native recipients, non-native grasses were twice as suppressive as native grasses (22% vs 11%, respectively). The Phylogenetic Distance Hypothesis was supported by our finding of a significant correlation between phylogenetic distance and allelopathic impact. The Biotic Resistance Hypothesis was not supported. Overall, this meta-analysis adds to the evidence that allelochemicals may commonly contribute to successful or high impact invasions in the grass family. Increased awareness of the role of allelopathy in soil legacy effects associated with grass invasions may improve restoration outcomes through implementation of allelopathy-informed restoration practices. Examples of allelopathy-informed practices, and the knowledge needed to utilize them effectively, are discussed, including the use of activated carbon to neutralize allelochemicals and modify the soil microbial community.
It is well-known that soil allelotoxicity and the water stability of soil structure are determined by the entry of plant residues into the soil, but the relationship of these soil properties has not been investigated. Soil samples from the fields of the Federal Research Center "Nemchinovka" after growing 25 cultivars of spring and winter wheat on plots with sod-podzolic soil are selected in this study. The effect of the soil's allelotoxicity of plot samples on the germination of spring wheat seed of the Liza cultivar is studied by the biotesting method. The water stability of the soil structure is determined for the same samples. The existence of a sigmoid dependence between the allelotoxicity of soil samples and their water stability with a correlation greater than 95% is established. The presence of this dependence is apparently related to the increase in the soil's water stability with an increase in the amount of fresh plant residues entering them, which is known from the literature, and the transition of the allelotoxins' effects from stimulation to suppression with a growth in their concentration in soils.
The influence of soil allelotoxicity on the application efficiency of a sorption-stimulating preparation used for pre-sowing seed treatment was studied. A comparison was also made of the negative effects of allelotoxicity of soils and water extracts from these soils on the seed development. From the analysis of the results, it followed that the development of seeds is influenced only by allelotoxins contained in the soil in the immediate vicinity of plants, entering them, apparently, due to exchange sorption. This mechanism of interaction of soil allelotoxins with plants explains well the effectiveness of stimulating pre-sowing seed treatment with sorption preparations, the sorption capacity of which is several orders of magnitude less than the amount of allelotoxins contained in the soil. A comparison was made that effect of sorption-stimulating preparations during the pre-sowing treatment of seeds and when introducing into the soil 30 times larger quantities. It was found that result of the preparations use does not depend on the method of their application, which confirms the correctness of the proposed mechanism of interaction between soil allelotoxins and plants. Results analysis of the introduction into the soil the sorption-stimulating preparations suggested the existence of a microbiological factor in reducing the allelotoxicity of soils, the use of which made it possible to significantly increase the effectiveness of the sorption-stimulating preparations.
Implementation of plant extracts that are rich in phytochemicals and have the allelopathic potential for weed management could help reduce the use of chemical herbicides. The present study investigated the herbicidal potential of walnut (Juglans regia L.) leaf extract (WLE) against two weeds, Amaranthus retroflexus L. and Chenopodium album L., by testing in vitro their seed germination and seedling growth, and then evaluated in vivo the oxidative stress of potted plants. The effects of the walnut leaf extract were also tested on maize (Zea mays L.) to eliminate possible negative impacts on a cultivated plant. Total phenolic acids and total flavonoid content in the extract were determined in prior bioassays, followed by separation and analysis of flavonoids and phenolic acids by high-performance liquid chromatography (HPLC). Phytochemical analysis revealed that the obtained extract was notably rich in phenolic compounds, while HPLC analysis confirmed the presence of (+)-catechin, luteolin, myricetin, rutin, (–)-epicatechin, genistin, protocatechuic acid, and caffeic acid as major extract components. The results obtained in bioassays revealed a significant negative impact of the walnut leaf extract on germination and seedling growth of the tested weeds, as well as significant oxidative stress in weeds grown in pots. Although it affected the maize seedling growth in vitro similar to the tested weeds, maize germination was less sensitive to treatment, and the extract did not have a significant negative impact in terms of oxidative stress in maize plants grown in pots. The findings show that walnut leaf extract may have a promising role in replacing chemical herbicides in maize.
Allelochemicals have been proposed as environmentally friendly bioherbicides, but their short persistence in soils often limits their performance as natural weed management products. In this study, incorporation into organoclay granules was investigated as a strategy to protect the allelochemical scopoletin from rapid biodegradation and prolong its persistence in soil. The commercial organoclay Cloisite® 10A, in its raw powder form, was used to prepare the granules. A kinetic study revealed slower sorption of scopoletin on the granules than on the organoclay powder and indicated an intraparticle pore diffusion mechanism. The half-life of scopoletin in soil under laboratory conditions increased significantly by incorporating the allelochemical into the organoclay granules, from 0.34 to 14.4 days. A field experiment was also conducted to assess whether the increase in soil half-life measured under controlled laboratory conditions translated to field conditions and to compare the phytotoxicity of the granulated allelochemical with that of its free (dissolved) form. The addition of scopoletin-loaded organoclay granules to soil plots rendered a field half-life for the allelochemical of 20.1 d, in contrast to 0.54 d obtained for its free form. The granules also favored the expression of the phytotoxicity of scopoletin, reducing germination and root growth of Lactuca sativa L. to a greater extent than free scopoletin. The results of this work indicate that incorporation into organoclay granules could be a suitable technological approach to provide allelochemicals with protection from rapid biodegradation losses in soil, which may help increase their persistence for a better performance as crop protection products.
The influence of various types of impacts on soil samples on the germination of seeds and the development of seedlings in comparison with sand (allelotoxicity) was studied. It is established that various types of soil sample preparation can significantly affect their allelotoxicity. It is shown that initial soil stimulated seedling development (+23%). Drying to air-dry state with further wetting increased the allelotoxicity to -27%. Autoclaving of samples (148°C, 4.5 atm) increased their allelotoxicity to -77%. The data obtained suggest that allelotoxins can exist in the soil in active and fixed forms and pass from the fixed form to the active form under various types of impacts on the soil. The study of the influence of the allelotoxicity of soil samples on the application efficiency of sorption-stimulating preparation (SSP), used for the pre-sowing treatment of spring wheat seeds, shows that the application effect of SSP monotonically decreases when allelotoxicity increases. The calculations show that the amount of sorbent used to protect seeds from allelotoxins is 3-4 orders of magnitude lower than the amount that can fix allelotoxins contained in soils. It follows from above that the development of seed seedlings is affected only by a small part of allelotoxins present in soils in the active state.
The effect of pre-sowing treatment of spring wheat seeds with suspensions of various actinomycete strains has been studied. It has been found that 4 out of 18 strains studied had a stimulating effect on seed germination in soils and plant development. The stimulation of seeds by these strains was not observed during seed germination in sand. It has been suggested that the mechanism of acceleration of seed development by actinomycetes could be based not only on the release of stimulating biologically active substances, but also on the consumption of allelotoxins by these microorganisms. The test carried out to study the possibility of actinomycete growth on a medium containing one of the most common allelotoxins, coumarin, has shown that actinomycetes promoting seed germination develop on this medium more intensively compared to strains that do not affect or inhibit the germination of spring wheat seeds. This confirms the proposed hypothesis that actinomycetes can stimulate seed germination through consumption of soil allelotoxins.
The phytotoxicity of soils under Wedelia trilobata has been described, but the dynamic between phytotoxic and metabolites in W. trilobata soil and the restriction posed by soil properties have been poorly addressed. In this study, the phytotoxic variation of W. trilobata soil in response to the changes in soil properties and soil metabolomics was determined at monthly intervals for 11 months using bioassays and metabolomic approaches. Strong variability in soil properties and obvious temporal variations in the soil phytotoxicity were observed over the 11‐month period. Among the soil properties that were analyzed, soil organic matter, electrical conductivity, total nitrogen, and soil nutrients presented the most contribution in differentiating soils according to time of sampling and strength of phytotoxicity. Nonsterilized soil exerted stronger percentage inhibition of seed germination (IG) of lettuce, whereas the percentage inhibition of shoot height (SH) and root length (RL) of lettuce was higher in sterilized soil. Decline in the overall phytotoxicity was clearly observed in nonsterilized soil, suggesting the role of soil microbes in mediating the soil phytotoxic effect of W. trilobata, albeit the negative correlation. Putative metabolites contributing to the discrimination of soils according to time of sampling and strong correlation with percentage inhibition (%) of IG, SH, and RL were identified and discussed. Overall, the results showed that the phytotoxicity of soils under W. trilobata varied throughout the 11 months of study and can be restricted by the changes in soil properties.
A rapid degradation of 2-(3H)-benzoxazolinone (BOA) in aqueous media by root-colonizing bacteria of Avena sativa is described. 2-Amino-3H-phenoxazin- 3-one and 2-acetylamino-3H-phenoxazin-3-one were identified as microbial decomposition products. o-Aminophenol was detected as an intermediate. This microbial degradation was also observed when roots of Secale cereale were incubated in aqueous 0.5 mM BOA solutions in contrast to Triticum aestivum and Vicia faba. With Avena sativa phytotoxic effects of 0.125 mM and 0.25 mM 2-amino-3H-phenoxazin-3-one were proved by radicle elongation assays. Nevertheless, the inhibitory influence of BOA is significantly reduced due to the microbial degradation process. The possible physiological importance of the species dependent microbial metabolization of this allelochemical is discussed.
Black walnut toxicity to crop plants was found to be due to the juglone (5-hydroxy-1, 4-naphthoquinone) in the tree (5). Cook (3) and Massey (9) suggested that toxic material came from the roots of the walnut tree. Bode (2) believed that the toxin came from the leaves. However, the quantity of juglone in the different parts of the walnut tree has not been fully established. Daglish (4) conducted experiments on Juglans regia , in which he suggested that juglone existed in the plant as glucoside of 1,4,5-trihydroxynaphthalene. On hydrolysis it yielded glocose and alpha-hydrojuglone.. This non-toxic hydrojuglone is oxidized to its toxic juglone from exposure to the air or some oxidizing substance from roots of other plants (6). Recent experimental data (Wang, unpublished) showed that 10 ppm commercially purified juglone reduced tomato seedling growth by 50 per cent when roots were immersed in the solution. A 100 ppm application killed the seedlings.
Acidic fractions of the extracts from the three alfalfa cultivars Batasu, Rasen, and Yuba exhibited a varietial difference in the inhibitory effect on hypocotyls and radicle growth of alfalfa (cv. Nasuwakaba) and rice (cv. Koshihikari) seedlings. The extract from Rasen possessed the strongest inhibitory activity, and that of Batasu was the lowest. In a TLC bioassay with lettuce seedlings, inhibitory zones of the extracts were located at an Rf value of 0.6-0.8, and maximum exhibitory zones at Rfs of 0.7-0.8. However, the extracts of Rasen and Yuba contained an additional inhibitory zone at Rf of 0.1-0.2. Inhibitory zones were analyzed by HPLC. Eight phenolic compounds were identified in the extracts from Rasen and Batasu, and six compounds in that from Yuba. However, the content of these phenolic compounds varied with the cultivar. The content of each phenolic compound was the highest in Rasen, followed by Yuba and Batasu, although the content of p-hydroxybenzoic acid was equivalent in all cultivars. We suppose that the degree of inhibitory exhibition of allelopathy may be related to the presence and concentrations of allelochemicals (phenolic compounds), however, the allelopathic activity of the plant might be determined by interactions of all these compounds, not just a single chemical.
The overuse of herbicides and insecticides in agricultural practice has caused environmental pollution, human health problems and unsafe agricultural products.
The ability of phytopathogenic fungi to overcome the chemical defense barriers of their host plants is of great importance for fungal pathogenicity. We studied the role of cyclic hydroxamic acids and their related benzoxazolinones in plant interactions with pathogenic fungi. We identified species-dependent differences in the abilities of Gaeumannomyces graminis var.tritici, Gaeumannomyces graminis var.graminis, Gaeumannomyces graminis var.avenae, and Fusarium culmorum to detoxify these allelochemicals of gramineous plants. The G. graminisvar. graminis isolate degraded benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benzoxazolin-2(3H)-one (MBOA) more efficiently than did G. graminis var.tritici and G. graminis var. avenae. F. culmorum degraded BOA but not MBOA.N-(2-Hydroxyphenyl)-malonamic acid andN-(2-hydroxy-4-methoxyphenyl)-malonamic acid were the primary G. graminis var. graminis andG. graminis var. tritici metabolites of BOA and MBOA, respectively, as well as of the related cyclic hydroxamic acids. 2-Amino-3H-phenoxazin-3-one was identified as an additional G. graminis var. triticimetabolite of BOA. No metabolite accumulation was detected forG. graminis var. avenae and F. culmorum by high-pressure liquid chromatography. The mycelial growth of the pathogenic fungi was inhibited more by BOA and MBOA than by their related fungal metabolites. The tolerance ofGaeumannomyces spp. for benzoxazolinone compounds is correlated with their detoxification ability. The ability ofGaeumannomyces isolates to cause root rot symptoms in wheat (cultivars Rektor and Astron) parallels their potential to degrade wheat allelochemicals to nontoxic compounds.
Allelopathy plays an important role in the agroecosys-tems leading to a wide array of interactions between crop-crop, crop-weed and tree-crops. Generally, these interactions are harmful to the receiver plants but provide a selective benefit to the donor. Soil microbes play a key role in determining such interactions as they not only alter the nature of allelopathic interactions but also modify the expression of allelochemicals. Soil sickness problem in the croplands could also be attributed to the allelopathic property or even the autotoxicity. The allelochemicals released largely by the plant residues that are left in the fields after the harvest of crops add to the multifarious problems. If properly managed, these residues could be used for controlling weeds and pests. As is true for any chemical based response, allelopathic interactions are also concentration specific. The promotory functions that are inbuilt need to be worked out and exploited. Now a days allelopathic interactions, in general, and the allelochemicals, in particular, are viewed as an important tool for sustainable weed and pest management, and disease control. In this direction, a number of strategies like use of cover or smother or companion crops for weed management, direct use of allelochemicals as natural pesticides, and even the transfer of allelopathic traits/principles to modern day cultivars are being adopted. The purified allelochemicals and/or their derivatives and even the compounds synthesized on their chemistry can be used as novel agrochemicals for sustainable management in an eco-friendly manner. The present paper aims to discuss all the above mentioned roles and aspects of allelopathy in the agroecosystems.
Analysis of small-scale distribution may allow allelopathic interaction among plant species to be distinguished from competitive interaction. If all environmental factors except slope are uniform, allelopathy produces spatial asymmetry in the association with a hypothetical receptor species and the corresponding hypothetical emitter species in the neighborhood of the latter. The interaction betweenRumex obtusifolius and the meadow speciesLolium perenne, Poa pratensis, Dactylis glomerata, andTrifolium repens is analyzed by way of example.
Phenolics are one of the many secondary metabolites implicated in allelopathy. To establish that allelopathy functions in a natural ecosystem, the allelopathic bioassay must be ecologically realistic so that responses of appropriate bioassay species are determined at relevant concentrations. It is important to isolate, identify, and characterize phenolic compounds from the soil. However, since it is essentially impossible to simulate exact field conditions, experiments must be designed with conditions resembling those found in natural systems. It is argued that allelopathic potential of phenolics can be appreciated only when we have a good understanding of 1) species responses to phenolic allelochemicals, 2) methods for extraction and isolation of phenolic allelochemicals, and 3) how abiotic and biotic factors affect phenolic toxicity.
The importance, characteristics, positive and negative impacts, and future role of weeds as an integral part of the natural and agroecosystems are evaluated and discussed. Interference between plants in nature and the importance of differentiating between competition and allelopathy are interpreted. Allelopathy as one component of weed/crop interference, allelochemicals from weed species and their possible mechanism of action are listed and discussed. Weed species with inhibitory action against cultivated crops, other weed species, and plant pathogens, as well as self-inhibitory (autopathic) species are reviewed. Stimulatory or inhibitory allelopathic effects of different crop plants, trapping and catching species, and the potential of allelopathic weeds in inhibiting or stimulating certain parasitic weed species are discussed and evaluated. Allelopathy as a mechanism and future strategy for agricultural pest control and farm management and the potential use and development of some allelochemicals as natural pesticides or plant growth regulators are also considered and discussed.
The relationship between the adsorption of phenolic substances In soils and the chemical structures of phenolics or the type of soil were Investigated by batch and column methods. Fifteen soil samples containing kaolinic, montmorillonltlc, and allophanic clay minerals and 6 phenolic acids, P-hydroxybenzolc, vanillic, p-coumaric, ferulic, protocatechuic, and a-resorcyllc acids were used for the study. The soil samples were collected from the plough layer of crop fields and the sublayer of uncultivated soils. The behavior of phenolic substances in liolls was also discussed. The results are as follows:
1) The adsorption of phenolic acids was influenced by the type of soil. In the case of both arable Bolls and subsoils, allophanic soils adsorbed more phenolic acids than kaolinic and montmorillonitic soils.
2) The adsorption of phenolic acids was also influenced by the chemical structures of the phenolic substances. Among the phenolic acids used, protocatechuic acid was adsorbed in the largest amount, and the importance of the catechol moiety for the adsorption of phenolics or humic acid was Indicated.
3) From these results, it was tentatively concluded that in mineral arable solis most phenolics exuded from plant residues or produced during the decomposition process were rapidly leached with water from the surface horizon of the soil, and that in humus-allophanic arable salls, these phenolics, especially polyphenolic compounds, were largely adsorbed, thus contributing to humus formation.
4) Among arable soils, organic matter content correlated highly with the adsorption of each phenolic acid. Subsoils with extremely low organic matter contents, however, adsorbed greater amounts of each phenolic acid than arable loils for all types of soils.
5) The other properties of soils such as pH value, clay and free iron contents were not closely related to the adsorption of phenolic acids.
Myrosinase (thloglucoside glucohydrolase; EC 3.2.3.1) is an enzyme that hydrolyzes glucosinolates to D-glucose and allelochemicals that have biological potential to suppress weed seed germination in soil. This enzyme, found in some microorganisms and released to soils via root exudation and decomposition, can be assayed by adding sinigrin (2-propenyl-glucosinolate) to soil as a substrate. We describe a simple and rapid method to assay myrosinase activity in soils. In this method, 1 g of soil is treated with toluene (0.2 mL) and incubated at 37°C with 2.8 mL of a buffered solution (pH 7) of sinigrin (20 mM final concentration) for 4 h. Glucose released upon sinigrin hydrolysis is extracted and its concentration is measured spectrophotometrically. Tests showed that recovery of glucose was quantitative if toluene was included in the assay mixture. Myrosinase activity in five soils studied ranged from 71 to 338 μg glucose g -1 soil 4 h -1. The rate of sinigrin hydrolysis increased with temperature from 10 to 40°C. The activation energy of myrosinase in four soils ranged from 40.3 to 52.8 kJ mol -1. The V max values for sinigrin hydrolysis calculated by the three linear transformations of the Michaelis-Menten equation ranged from 76 to 518 (avg. 275) μg glucose g -1 soil 4 h -1 and the apparent K m values for myrosinase ranged from 5.3 to 12.9 (avg. 8.1) mM. The method developed in this study is accurate, fast, and simple.
Higher plants with strong allelopathic properties are commonly incorporated into soil for weed-control purposes. To understand the phytotoxic variation in the soil, which can be utilized for weed control through the use of allelopathic plants, the decomposition of alfalfa (Medicago sativa L. cv. Rasen) and kava (Piper methysticum L.) after soil amendment were evaluated. Both alfalfa and kava strongly inhibited barnyardgrass and monochoria growth for up to 10 days (80–100 % weed control). After 20–25 days, the magnitude of inhibition was drastically reduced, but was still effective (50 % weed control). A number of phenolic acids were detected in the soil even 50 days after incorporation in low concentration, but their concentrations reached a maximum after 10–15 days and were efficacious until 20–25 days. Phenolic acids varied between alfalfa and kava. The variations in electrical conductivity (EC) and osmotic pressure (OP) were strongly related to chemicals and toxic compounds exuded into the soil during decomposition and were proportional to the magnitude of inhibition observed, whereas pH did not appear to be correlated with inhibition. The decomposition of several unknown inhibitors present in kava was also analysed and assessed. Our findings indicate that these growth inhibitors were almost disintegrated in soil after 10 days, but strong inhibition was detected until 25 days after amendment. Results from this study demonstrate that chemicals released from allelopathic plants incorporated into soil are toxic and cause inhibition of certain species and could be exploited as a biological tool for weed management.
Four higher plants, namely glory bowers (Clerodendrum trichotomum L.), jimsonweed (Datura stramonium L.), beggarweed (Desmodium triflorum L.) and Chinaberry (Melia azedarach L.), with the strong allelopathic potential among 19 allelopathic species from Southeast Asia, were tested for their effects on weed emergence in paddy soil and field. In a greenhouse experiment, D. stramonium, D. triflorumand M. azedarach exhibited similar inhibitory magnitude at 1 t ha−1 achieving more than 90 % weed control. C. trichotomum achieved about 70 % weed reduction at 2 t ha−1. In paddy fields, D. triflorum was the most promising material for weed control and attained the highest rice yield among treatments, at the concentration of 2 t ha−1, whereas the inhibition of D. stramonium and M. azedarach was weakened in the greenhouse. No injury of rice plants was observed. These plants might be used as natural herbicides to reduce the dependence on synthetic herbicides.
Alfalfa (Medicago sativa L.) plants were found to contain water-soluble substances that inhibited the germination and seedling growth of alfalfa (Chung and Miller 1990, Agron. J. 87, 762-767). Tsuzuki et al. (1999, Rep. Kyushu Branch Crop Sci. Soc. Japan 65, 39-40) discovered allelochemicals in alfalfa plants that could have adverse effects on the growth of some lowland weeds. This study was conducted to investigate varietal differences in allelopathic potential in alfalfa plants. Eight common varieties of Japanese alfalfa (Medicago sativa L.), namely Batasu, Hisawakaba, Kitawakaba, Makiwakaba, Natsuwakaba, Lucerne, Tachiwakaba and Yuba, were grown by conventional methods in the Experimental Field of the Crop Science Laboratory, Faculty of Agriculture, Miyazaki University. Aqueous extracts of both fresh and dried material of alfalfa plants of all varieties significantly inhibited both germination and growth of lettuce (Lactuca sativa L.). Leachates from germinating seeds of almost all alfalfa varieties inhibited elongation of the radicle but produced a negligible increase in germination and only slightly inhibited elongation of the hypocotyl of lettuce plants. Results demonstrated that the degree of inhibition of germination and growth of lettuce varied with the variety of alfalfa. In particular, Lucerne was identified as having the strongest allelopathic potential of the varieties studied. The results suggested that the allelopathic potential of alfalfa might be relating to a gene.
Concerns about the health and environmental impacts of herbicide use have led farmers and researchers to seek alternative methods of weed management. One such alternative is the use of allelopathic cover crops, which release chemicals into the soil environment that can contribute to weed management through suppression of weed seed germination, seedling emergence and establishment, and seedling growth, in addition to providing other soil quality benefits to farmers. Brassicas, or members of the Brassicaceae, contain glucosinolates, sulfur-containing molecules that degrade to form compounds toxic to a variety of organisms. Glucosinolate content varies between brassicas grown as cover crops; mustards typically have very high glucosinolate content, whereas others, including canola and rapeseed, contain lower amounts. Brassica residues have strong phytotoxic effects; weed density and biomass has been observed to be lower in crops following incorporation of brassica residue. In addition to a literature review, this thesis describes two experiments that investigated the mechanisms behind this observed weed suppression by brassicas. The first experiment examined seedling establishment following incorporation of brassica residues and residues of other short-season cover crops. We hypothesized that all cover crop residues would decrease and delay seedling emergence compared to fallow and that emergence following the brassica residues would be lowest and slowest, particularly following the high-glucosinolate mustard. Based on the theory that smaller seeds are more susceptible to stress such as those imposed by allelopathic cover crops, we expected that smaller-seeded species would be affected more than larger-seeded ones. While average emergence was indeed lower following all of the cover crop residues compared to fallow, emergence was similar following the brassicas and following the other cover crop residues. Seed size was a poor predictor of species emergence following the cover crops. While emergence was slower following all the cover crop residues, emergence rates were generally similar between the brassicas and the other cover crops, although delayed emergence following mustard was observed in one year. The second experiment examined the effects of mustard and canola on the growth of established redroot pigweed and green bean plants and, in turn, on interspecific competition. Redroot pigweed and green bean, both alone and in mixture, were seeded into incorporated mustard and canola residues and fallow plots; plants were sampled throughout the season to assess the effects of the cover crop residues on growth. We hypothesized that growth of the smaller-seeded redroot pigweed would be harmed by the brassica residues, particularly early in the season, but that growth of the larger-seeded green bean would not be affected. In turn, we expected that the brassica residues would mediate interspecific competition, through differential effects on growth, thereby conferring a competitive edge to green bean plants growing with redroot pigweed. As expected, brassica cover crop residues did not affect green bean height, biomass, leaf area, relative growth rate, or final marketable yield. Contrary to expectations, these parameters for redroot pigweed were also unaffected. While the presence of competition reduced growth of both species, no interaction with cover crop residue was found.
The changes in amount of ether-extractable phenolic substances, individual phenolic adds, organic matter content, and pH value in the decaying process of rice straw were compared at 10, 30, and 50°C under moist and flooded conditions for 70 days. 1) The changes in pH value with time varied markedly according to temperature and water conditions. 2) Phenolic substances in the ether-extractable fraction obtained from the acidified solution of alkaline methanol extract contained undetected phenolic compounds in amounts larger than the phenolic adds detected by gas chromatography. pH value during incubation was hardly attributable to these phenolic substances because of their small quantity. 3) The changes in amount of the ether-extractable phenolic substances with time was mainly due to phenolic compounds other than phenolic acids, and influenced largely by the temperature and water conditions. Their formation and degradation took place rapidly at high temperatures under flooded conditions. 4) From the plots of individual phenolic acids vs. time, it was tentatively concluded that phenolic acids contalned in non-decayed straw were rapidly degraded in the earlier stage, and some of them were newly produced from ether-unextractable precursors in the later stage. These reactions occurred rapidly at high temperatures, especially under flooded conditions. 5) The content of p-hydroxybenzolc acid increased simultaneously with a rapid decrease in p-coumaric acid during the incubation ot straw. The relationship between vanillic acid and ferulic acid was the same.
Roots of many weed and crop species contribute biologically active chemicals into the environment known as root exudates. Root exudates are known to influence growth and establishment of crop and weed species, and these are released from living root systems. Many perennial woody and herbaceous plants have deep and extensive root/rhizome subterranean systems, which can produce prolific amounts of root exudates over long periods of time. Root exudates contribute many types of organic compounds to the rhizosphere. In addition to simple and complex sugars and growth regulators, root exudates contain different classes of primary and secondary compounds including amino acids, organic acids, phenolic acids, flavonoids, enzymes, fatty acids, nucleotides, tannins, steroids, terpenoids, alkaloids, polyacetylenes, and vitamins (Table 10.1; Rovira 1969; Schönwitz and Ziegler 1982; Rice 1984; Uren 2000). Uren (2000) suggested that the amount of root exudates produced varies with the plant species, cultivar, the age of the plant, and substrate and stress factors.
Allelopathic substances in alfalfa plants (Medicago sativa L.) were purified from methanol extracts of alfalfa shoots. The methanol extracts were fractionated into an acidic fraction, and the sample was divided into 10 fractions by thinlayer chromatography (TLC). Growth of radish seedlings was inhibited by the substances obtained from Rf values of 0.5∼0.6 and 0.6∼0.7. These fractions were eluted with distilled water, and the eluates were analyzed by high-performance liquid chromatography (HPLC). Six peaks were detected on the chromatogram. Growth of radish seedlings was inhibited on three peaks. Of these peaks, two were identified using HPLC, a mass-spectrometer, IR, and 1NMR as follows : peak b, ferulic acid and peak f, salicylic acid. The growth of alfalfa and radish seedlings was inhibited at lower concentrations of these substances.
P-Coumaric, ferulic, vanillic, and p-hydroxybenzoic acids, the main phenolics in rice straw and its decayed products, were incubated at 50°C at concentrations of 30 ppm in dilute water-extract solutions of decayed straw and soil. The dynamics of the individual phenolics and their degradation producta were studied, and the fate and behavior of each phenolic acid in the decaying process of plants were also discussed. The following results were obtained: 1) These phenolic acids were degraded rapidly in a short period. Their half lives were less than 10 days under the experimental conditions used here. 2) The degradation rates of p-hydroxybenzoic and p-coumaric acids were approximately the same in both extract solutions of decayed straw and soil, but vanillic and ferulic acids, which contain methoxy groupings, disappeared much more rapidly in the soli extract solution than in the decayed straw extract solution. 3) When these 4 phenolic acids were added all together into the decayed straw extract solution, they were degraded more slowly than in solutions of individual acids, especially p-coumarlc and ferulic acids which are cinnamlc acid derivatives. 4) A major degradation product of p-coumaric acid, after treatment with diazo-methane, was isolated by preparative gas chromatography and determined as p-methoxycinnamic acid methylester by IR spectroscopy and mass spectrometry. The product itself was identified as p-methoxycinnamic acid by co-chromatography with the authentic sample. A major degradation product ot ferulic acid was Identified as 3, 4-dimethoxycinnamic acid in the same way. 5) p-coumaric and ferullc acids were transformed rapidly to large amounts of p-methoxycinnamic and 3, 4-dimethoxycinnamic acid, respectively, by probably reveraible reactions. These in turn were gradually transformed into small amounts of p-hydroxybenzoic acid and vanillic acid, respectively. p-hydroxybenzoic acid was rapidly transformed to protocatechuic acid. Vanillic acid was rapidly degraded, but no product was detected by gas chromatography. 6) The possible degradation pathway of these phenolic acids in the decaying process of planta is presented.
To exert phytotoxic effects on other plant species, chemicals may have to move to the roots of the target plant through the soil. However, during movement, abiotic (physical and chemical) and biotic (microbial) soil barriers can limit the phytotoxicity of chemicals in terms of quality and quantity required to cause injury. Organic matter, reactive mineral surfaces, ion exchange capacity, inorganic ions, and abiotic and biotic factors of soil environment significantly influence allelochemical activity. In this article, the significance of soil in laboratory and field studies on allelochemical interference is discussed.
Plant residues may have allelopathic effects on the growth and yield of subsequent plants during their decomposition. Such effects have been attributed to phytotoxic chemicals leached from the residues together with toxins produced by micro-organisms during residue decomposition. In order to increase our understanding of this phenomenon and provide valuable predictive tools for practice, a mechanistic model of residue allelopathy has been developed which simulates allelopathic phenomena caused by decaying plant residues. The model provides an integrated views of the phytotoxic pattern of plant residues during decomposition, in terms of both the responses of a receiver plant and allelochemical dynamics in the environment. Its comparisons with observed data from the experiments conducted at different conditions are satisfactory.
Previous studies have shown that phenolic compounds are potentially allelopathic and present at low concentrations in soil solution. This study was conducted to evaluate the Folin and Ciocalteu's method for determining concentrations of phenolic C in aqueous and citrate extracts of soils containing 7.1 to 57.9 g kg -1 organic C. Soils were reacted for 18 h with a 0.3 mM phenolic acid mixture or DI-H 2O to serve as a control. Folin and Ciocalteu's reactive-phenolic C content in the DI-H 2O control extracts suggested positive interference from dissolved organic matter rather than free phenolic compounds desorbed from the native soils. The absorptivity of the Folin and Ciocalteu's reduced complex was 1128 ± 25 L mol -1 cm -1 for the phenolic acid mixture and 45 ± 8 L mol -1 cm -1 for soluble organic matter ligands. Although the method has much higher sensitivity to phenolic acids than to organic matter, the higher concentration of organic matter results in substantial background positive interference. However, multiple regression equations of corrected Folin and Ciocalteu's absorbance (phenolic- treated absorbance minus deionized water control absorbance) regressed with solution parameters had excellent fits (R 2 > 0.97). This suggests that interference correction is possible in aqueous extracts. The Folin and Ciocalteu's reactive-phenolic C concentration in the citrate extracts of the phenolic acid mixture-amended soils were not significantly different from the DI-H 2O control soil extracts indicating that the Folin and Ciocalteu's method is not suitable for use with soil citrate extractions. The large quantity of organic matter extracted by citrate probably masks absorbance due to any extracted phenolic compounds.
The accepted criteria for identifying allelopathic interactions in the field that have been proposed in the literature offer heuristic function, but to date have failed as a framework for research and diagnostics. If the present criteria are to be modified to make them useful empirically, their shortcomings must be identified. For this review, data from the literature and from defined model systems consisting of plants, soil, and/or microbes are used to evaluate the applicability of the accepted criteria to defined systems in which plants are responding to known allelochemicals. Based on this evaluation, modified criteria are proposed. In many respects, however, the modified criteria are as difficult to satisfy in the field as those proposed previously. The new criteria have value as a research framework because they clearly suggest that a shift in research focus to the soil environment, specifically the barrier of the rhizosphere through which allelochemicals must pass, is essential if the role of allelopathic interactions in the field is to be established.
Nonsterile soil transforms the rye metabolite 2(3H)-benzoxazolone (BOA) into 2-amino-3H-phenoxazin-3-one, which is an order of magnitude more toxic to barnyard grass than benzoxazolone. Benzoxazolone was recovered unchanged from sterile soil. However,o-aminophenol is converted to aminophenoxazinone by both sterile and nonsterile soil in the presence of air. Aminophenoxazinone is probably produced by microbial hydrolysis of benzoxazolone intoo-aminophenol, which is oxidized to aminophenoxazinone in both sterile and nonsterile soil. No 2,2'-oxo-1,1'-azobenzene was found in any incubations of soil with benzoxazolone,o-aminophenol, oro-azophenol.
The defensive cyclic hydroxamates 7-methoxy-2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIMBOA) and 7,8-dimethoxy-2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIM2BOA) of wheat and corn are transformed in nonsterile soil, via 6-methoxy-2(3H)-benzoxazolone (MBOA) and 6,7-dimethoxy-2(3H)-benzoxazolone (M2BOA) respectively, into 2-amino-7-methoxy-3H-phenoxazin-3-one and 2-amino-4,6,7-trimethoxy-3H-phenoxazin-3-one. The soil transformation is similar of that undergone by the rye metabolite 2(3H)-benzoxazolone (BOA) into 2-amino-3H-phenoxazin-3-one. The transformations to phenoxazinones are not observed in sterile soil. The 2-amino-3H-phenoxazin-3-one inhibits barnyard grass radicle elongation, but the methoxylated aminophenoxazinones are not significantly inhibitory.
Relationships between abiotic oxidation and adsorption of phenolic acids added to soils and soil chemical properties were investigated by using 32 soil samples and ferulic, vanillic, and p-hydroxybenzoic acids. Soil properties studied were as follows: (as adsorption factors) contents of acid oxalate extractable Al (Alo), Fe (Feo), dithionite-citrate-bicarbonate (DCB) extractable Fe (Fed), total carbon and clay, and (as oxidation factors) level of soil oxidative activity (Cr oxidation) determined by the amount of Cr(VI) converted from Cr(III) added to soils. Soil samples were divided into 3 types based on chemical properties: Andosols A (A horizon of Andosols), Andosols B (B horizon of Andosols and light-colored Andosols), and non-Andosols.The recovery of all phenolic acids (RPA) was negatively correlated with the total carbon and Feo contents in Andosols A and B, respectively, which suggested adsorption onto soil organic matter in Andosols A and onto Feo in Andosols B. It was considered that almost no oxidation of phenolic acids occurred in Andosols A, because a very small amount of Cr(VI) was obtained. The recovery of ferulic acid (RFA) and vanillic acid (RVA), however, was negatively correlated with Cr oxidation in non-Andosols, suggesting that these phenolic acids were oxidized, while almost all of the p-hydroxybenzoic acid was recovered.These results were also supported by the comparison between RFA and recovery of dissolved organic carbon (RTOC). RFA was very similar to RTOC in Andosols A and B, which indicated that adsorption occurred, whereas RFA was lower than RTOC in the non-Andosols that showed a high level of Cr oxidation, indicating that oxidation took place. Manganese dissolution which occurred when phenolic acids were added to soils was also examined.
Plant phenolic acids are found in soils and their importance has been implicated in various soil processes, including biochemical weathering of minerals, humus formation, interactions between plants (allelopathy), and nutrient availability to plants. P ‐hydroxybenzoic, vanillic, p ‐coumaric, and ferulic acids were added to soils at a rate of 5.15 mmol/kg, extracted with Mehlich III extractant immediately and on Days 1, 2, 4, 8, 16, and 32, and quantified by high‐performance liquid chromatography. The recovery of phenolic acids from Cecil (Typic Hapludults, clayey, kaolinitic, thermic), Portsmouth (Typic Umbraquualts, fine loamy, mixed, thermic), and White Store (Vertic Hapludalfs, fine, mixed, thermic) soils varied with soil type, horizon (A1 and B1), time, and type of functional group present on the aromatic ring. There was significant instantaneous sorption of all compounds in all soils; in A1 horizon materials, recovery decreased as soil organic matter increased. There was generally greater sorption of phenolic acids in the A1 horizon materials than in the B1 horizon materials of a particular soil type. Significant declines in recovery occurred with time for all phenolic acids in each type of soil, irrespective of horizon. The sharpest decline in recovery of phenolic acids from soils generally occurred within 2 d after addition of the compounds. The presence of methoxy groups and acrylic side chains on the aromatic ring of phenolic acids increased the “sorption” of these compounds in soils. Sorption of the phenolic acids by the various soils was generally in the order of p ‐hydroxybenzoic ≤ vanillic < p ‐coumaric < ferulic.
Phenolic acids are intermediary metabolites of many aromatic chemicals and may be involved in humus formation, allelopathy, and nutrient availability. Depending on their structures, six phenolic acids were shown to react at different rates with oxidized forms of Fe and Mn in a Palouse soil (fine-silty, mixed, mesic Pachic Ultic Haploxeroll). Increasing methoxy substitution on the aromatic ring of phenolic acids increased the reaction rate. Reaction rate was also increased for longer carboxyl-containing side chains. After 4 h reaction, little of the applied (10 mg kgâ»Â¹ soil) p-hydroxybenzoic or p-coumaric acids had reacted, while 0 to 5, 70, 90, and 100% of the vanillic, ferulic, syringic, and sinapic acids, respectively, had reacted. After 72 h under conditions limiting microbial growth, none of the p-hydroxybenzoic, 30% of the p-coumaric, and 50% of the vanillic acids had reacted. The reaction was shown to be predominantly chemical, and not biological, since phenolic acid extractabilities were similar for Palouse soil and for Palouse soil pretreated with LiOBr to remove organic matter. When the Palouse soil was pretreated with a sodium dithionite-citrate solution to remove Fe and Mn oxides, none of the phenolic acids reacted after 1 h. The reaction of sinapic acid with Palouse soil was shown to produce Fe(II) and soluble Mn as reaction products. The reaction of phenolic acids with soil was thus shown to be an oxidation of the phenolic acids, coupled with a reduction of soil Fe and Mn oxides.
Previous studies have suggested that phenolics from legume green manures may contribute to weed control through allelopathy. The objective was to determine if red clover (Trifolium pratense L.) residue amended field soils expressed phytotoxicity to a weed species, wild mustard (Sinapisarvensis L.). Field plots involving incorporation treatments of wheat (Triticum aestivum L.) stubble or wheat stubble plus 2530kgha−1 red clover residue, were sampled at −12, 8, 21, 30, 41, 63, and 100 days after residue incorporation (DAI). Soil–water extracts (1:1, m:v) were analyzed for plant nutrients and phenolic content. Phytotoxicity of the extracts was measured using a laboratory wild mustard bioassay. There was a 20% reduction of radicle growth in the green manure treatment in comparison with the wheat stubble treatment, but only at the first sample date after residue incorporation (8DAI). The radicle growth reduction had the highest correlation with the concentration of soluble phenolics in the soil:water extracts. Bioassays using aqueous extracts of the clover shoots and roots alone predicted a radicle growth reduction of 18% for the quantity of clover amendment rate used in the field plots. The close agreement of the predicted and observed root growth reduction at 8DAI further supports clover residue as the source of the phytotoxicity. This study demonstrates that the potential exists for using legume green manures to reduce the amounts of synthetic herbicides needed for weed control.
Alfalfa seedlings (cv. Cimmaron) were aseptically grown in a glass test tube containing a nutrient salts solution and 14C-labeled sodium acetate into which filtered air was pumped. After five days of exposure to fluorescent light at 22°C, the alfalfa seedlings were removed, washed with cold water, and their saponins extracted. Mean yield of 14C-labeled saponins was 50.2 mg/2.2 g of seed, and mean activity of the 14C-labeled saponins was 5.1 × 104 dpm/mg. Thin-layer chromatography (TLC) of 14C-saponins indicated soyasaponin I, medicagenic acid-3,28 glucoside, and medicagenic acid 3-O-glucoside, plus several unidentified spots, whereas TLC of hydrolyzed saponins (aglycones) showed medicagenic acid, hederagenin, and soyasapogenol B. After 150 hr at 22°C, 17.0% of the 14C-labeled saponins added to a sterile clay loam soil were converted to 14CO2, whereas 54.5% of the saponins were converted to 14CO2 in the nonsterile soil. 14CO2 evolution from each of four nonsterile soils that were amended with 14C-labeled saponins was 57.4–69.9% after 14 days of incubation, and 2.4–24.0% of the added 14C-labeled saponin was recovered in the humic acid fractions from the soils. Only 1.0–2.1% of the 14C label was associated with microbial biomass, as estimated following chloroform fumigation of the soils. Use of 14C-labeled saponins should facilitate a better understanding of the fate of these compounds in soil.
Most plants synthesize antimicrobial compounds as part of normal plant development (i.e., phytoanticipins) or synthesize such compounds de novo when challenged by microorganisms (i.e., phytoalexins). The presumed role of these plant antibiotics is to protect the plant from disease. However, many phytopathogenic fungi have enzymes that can detoxify the phytoanticipins or phytoalexins produced by their host. This may be a means that these pathogens have evolved to circumvent resistance mechanisms based on the production of plant antibiotics. Many of the phytoanticipin- and phytoalexin-detoxifying enzymes produced by phytopathogenic fungi have biochemical and regulatory properties that would indicate the phytoanticipins and phytoalexins produced by their host are their normal substrates. In addition, their activity, enzymatic products, or transcripts can be detected in infected plant tissue suggesting that they are functioning in planta during pathogenesis. Specific mutations have been made by transformation-mediated gene-disruption procedures that eliminate the ability of Gaeumannomyces graminis var. avenae, Gloeocercospora sorghi, and Nectria haematococca to detoxify the phytoanticipins or phytoalexins produced by their hosts. The effect of these mutations on pathogenicity indicates a requirement for detoxifying enzymes in G. graminis var. avenae but not in G. sorghi or N. haematococca. Key words: disease resistance, pathogenicity mechanisms, isoflavonoids, saponins, cyanide.
Fusarium moniliforme, a fungus that commonly produces a symptomless endophytic association with most corn cultivars and inbred lines, was previously shown to catabolize 6-methoxy-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA), biologically active compounds produced by corn and known to be fungistatic. Studies were undertaken to isolate and identify the breakdown products of this decomposition. For each benzoxazolinone, a novel acid was isolated by column chromatography from 48-h old cultures of F. moniliforme. MS, NMR, and IR spectral data were used to identify the compounds as N-(2-hydroxyphenyl) and N-(2-hydroxy-4-methoxyphenyl) malonamic acids, products of BOA and MBOA, respectively.
Two sesquiterpene ketones, cyperotundone and α-cyperone, were isolated from dried tubers of purple nutsedge (Cyperus rotundus L.) as major constituents: ≈0.26% and 0.1% of dried tuber, respectively. These allelochemicals affect plant growth, but we consider that these terpenoids undergo modification when they are released into the rhizosphere from the donor plant. For the structure–activity relationship study, cyperotundone was oxidized with selenium dioxide in acetic acid to 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione. Subsequent hydrogenation of 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione gave hydroxylated derivatives, cyperotundon-2-ol and 3-hydroxy-4-patchoulene-2,6-dione, respectively. 4-Patchoulene-2,3-dione inhibited the hypocotyl growth of lettuce seedlings but promoted radicle elongation at 0.1−2 mg L−1 concentration without chlorosis. Moreover, this radicle elongation recovered with the addition of galactose and was not antagonized by gibberellin A3. The effect of 4-patchoulene-2,3,6-trione showed a similar chlorosis, caused by 3,6,9-sugetriol triketone, against lettuce seedlings. These ketones did not show the radicle elongation.
The ability of the maize pathogen Fusarium subglutinans to metabolize benzoxazolin-2(3H)-one (BOA) and 6-methoxybenzoxazolin-2(3H)-one (MBOA), important allelochemicals of Zea mays, was studied. Growth of mycelium was completely inhibited by 10 mM BOA and reduced by lower concentrations. In vitro the fungus completely degraded 1 mM concentrations of BOA and MBOA within 2 d. N-(2-hydroxyphenyl)-malonamic acid and N-(2-hydroxy-4-methoxyphenyl)-malonamic acid were identified as the main degradation products of these allelochemicals.