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Effect of Citrus reticulata blanco leaf extract on seed germination and initial seedling growth parameters of five home garden food crops
... Thus, seed germination can be inhibited by plant tissue's natural substances (Devlin & Witham, 1983;Abozeed, 1990;Gill, Nyawuame, & Ehikhametalor, 1992). In addition, phenolics, terpenoids, and alkaloids released from these plants have an inhibitory effect on germination and sapling growth (Sahoo, Jeeceelee, Lallinrawna, & Muthukumaran, 2015). This is consistent with the study results where three chemical compounds were found in S. selanica leaves, while no alkaloids were observed in S. selanica tubers. ...
AbstrakDioscorea bulbifera L. (Dioscoreaceae) merupakan salah satu tanaman invasif yang menciptakan masalah lingkungan. D bulbifera mengandung alelopati yang memengaruhi proses fisiologis pada spesies lain. Penelitian ini bertujuan untuk mengetahui pengaruh alelopati berbagai konsentrasi ekstrak daun dan umbi D. bulbifera L. terhadap perkecambahan biji Shorea selanica (Lam.) Blume. Metode yang digunakan adalah Rancangan Acak Lengkap (RAL) dengan sepuluh perlakuan dan tiga ulangan. Perlakuan yang diberikan adalah perbedaan konsentrasi ekstrak D. bulbifera 25, 50, 75, 100%, dan kontrol. Berdasarkan hasil uji skrining fitokimia, semua metabolit sekunder dalam ekstrak daun menunjukkan hasil yang positif. Senyawa golongan saponin, tanin, flavonoid, dan steroid/terpenoid terdeteksi dengan kuat sedangkan senyawa alkaloid kurang kuat. Senyawa fenol tersebut adalah fenol, 1,2-benzenediol (dalam ekstrak daun) dan fenol, 1,2-benzendiol, 1,4-benzendiol, dan 2-metoksifenol (dalam ekstrak umbi). Berdasarkan uji perkecambahan, ekstrak metanol umbi dan daun D. bulbifera berpengaruh nyata terhadap daya kecambah, koefisien kecepatan berkecambah, dan koefisien keserempakan berkecambah S. selanica. Konsentrasi yang menurunkan viabilitas biji terendah adalah pada konsentrasi 75% dan 100% dengan rata-rata daya kecambah 10,00 ± 6,32 % (pada ektrak umbi) dan 0,00 ± 6,32 % (pada ektrak daun). AbstractDioscorea bulbifera L. (Dioscoreaceae) is one of the most unutilized invasive plants. This plant contains allelopathy that affects the physiological process of native species. This study aimed to discover the type of allelochemical in D. bulbifera and its effect on seed germination of Shorea selanica (Lam.) Blume. The method used was a Completely Randomized Design with ten treatments and three replications. The treatment given was the different concentration of D. bulbifera extract of 25, 50, 75, 100%, and control. Based on phytochemical screening tests, saponin, tannin, flavonoid, and steroid/terpenoid compounds were detected in leaf and tuber extract. The total phenolic in leaf extract was more significant than that in the tuber extract of D. bulbifera but the type of phenolic compounds was lower. The phenolic compounds were phenol, 1,2-benzenediol (in leaf extracts) and phenol, 1,2-benzendiol, 1,4-benzendiol, and 2-methoxyphenol (in tuber extracts). Based on the germination test, it was found that the methanol extract from the tubers and leaf of D. bulbifera significantly affected the germination capacity, coefficient rate of germination, and simultaneity coefficient of germination of S. selanica. It was found that treatment of concentration of 75% and 100% resulted in the lowest seed viability reduction with an average germination rate of 10.00 ± 6.32% (in tuber extracts) and 0.00 ± 6.32% (in leaf extracts).
... Highest inhibitory effect on the root (-27.67) and shoot (-51.73) was observed in 100% extract concentration (Table 1). The findings also conform to the findings by Sahoo et al. (2015), where aqueous leaf extract of Citrus reticulate inhibit the root and shoot length of soybean, maize, paddy, chilli and lady's finger. Desai and Gaikwad (2015) also found that the litter leachate of Excoecaria agallocha cause inhibitory effect on the germination, root length, shoot length, seedling dry matter and vigour index of rice as the concentration of leachates increased. ...
... The 100 % extract concentration was most inhibitory to root (-27.67 %) and shoot length (-51.73 %) ( Figure 2). This finding also confirm to other findings, where aqueous leaf extracts of Citrus reticulata inhibits the root and shoot length of soybean, maize, paddy, chilli and lady's finger (29) and leaf extracts of Trevesia palmata inhibits the root and shoot length of maize and french bean (17). Likewise, the litter leachate of Excoecaria agallocha inhibits the germination, root and shoot length, dry matter and vigour index of rice with increase in extracts concentration (7) and the root and aerial parts of E. colona extracts inhibits the seedlings growth of rice and soybean (5). ...
We studied the allelopathic effects of Flemingia semialata Roxb. leaf aqueous extracts in laboratory bioassays and in pot experiments on the growth of maize (Zea mays L.) and rice (Oryza sativa L.). The leaf aqueous extracts stimulated growth and yield of maize but was inhibitory to rice. The 100 % concentration of extract was most inhibitory to the growth and biomass of rice. On the contrary, the extracts stimulated the growth and biomass of maize at all test concentration. Gas chromatography-mass spectrometry (GC-MS) analysis of F. semialata leaf litter revealed the presence of alkaloids, phenols, terpenoids, unsaturated fatty acids and many others compounds. The compounds detected in methanol extracts were : 2-Isopropyl-5-methylcyclohexyl 3-(1-(4-chlorophenyl)-3-oxobutyl)-C (38.36, %), in petroleum ether extracts major compound was : 2R-acetoxymethyl-1,3,3-trimethyl-4T-(3-methyl-2-buten-1-yl)-1T-cyclohexanol (24.04 %) and in chloroform extract major compound was : Z-2-Octadecen-1-ol (36.74 %). Allelopathic effects of extracts from the leaf of F. semialata may be due to the presence of above compounds identified by GC-MS analysis.
... Highest inhibitory effect on the root (-27.67) and shoot (-51.73) was observed in 100% extract concentration (Table 1). The findings also conform to the findings by Sahoo et al. (2015), where aqueous leaf extract of Citrus reticulate inhibit the root and shoot length of soybean, maize, paddy, chilli and lady's finger. Desai and Gaikwad (2015) also found that the litter leachate of Excoecaria agallocha cause inhibitory effect on the germination, root length, shoot length, seedling dry matter and vigour index of rice as the concentration of leachates increased. ...
The allelopathic potential of aqueous leaf extracts of Flemingia semialata Roxb. a leguminous herbs was used to examined its effect on growth and yield of Zea mays L. and Oryza sativa L. at different concentrations in laboratory bioassays. The extracts show both inhibitory and stimulatory effect on the test crops. Significant stimulatory effects were observed in 50 and 75 per cent concentration for root length and 25 per cent for shoot length in maize. Stimulatory effect on the root length of rice were observed at lower concentrations, however inhibitory effect were observed on the shoot length whereby the inhibitory effect increases with increase in the concentration of extracts. The inhibitory effect on biomass yield was observed at lower concentration in maize but inhibitory effect was more pronounced in rice at higher concentrations. Aqueous leaf extract of Flemingia semialata Roxb. performed better in maize than in rice.
... Lemon leaves firstly inhibited the germination, and even those germinated were unhealthy and not able to survive [2,3], concluded that the crucifer species like Raphanus sativus L., Brassica campestris L. and Brassica oleracea L. were sensitive to leaf aqueous extract of Parthenium hysterophorus [2,3]. Several researchers performed experiments on lettuce seeds germination against lemon peel extract which resulted in 0% seed germination [16], but the present study showed that the lemon peel extract possessed inhibitory effect on lettuce and showed 62.5% seed germination, but the seedlings did not grow normally and had retarded and stunted growth. These findings Values are mean ± standard deviation of forty replicates; *= significant at P<0.01; compared with control. ...
Secondary metabolites produced by different plants might inhibit or stimulate the growth and development of other plants present in its vicinity, this kind of interaction among plants termed as allelopathy. Lemon (Citrus limon) peels, flowers, and leaves were chosen for test extract preparation to check the seed germination and seedling growth of lettuce (Lactuca sativa L.) and cabbage (Brassica oleracea L. var. capitata L. f. alba D C.) and to observe their allelopathic potential. The experiment was conducted in sterilized Petri dish; germination of seeds was observed for ten days and the shoot length, root length and number of germinated seeds was evaluated. The effects of different concentrations of aqueous extract were compared to distilled water (control). The results showed maximum seed germination in control whereas all the test extracts showed very low germination percentage except lemon flower extract on cabbage seeds showing 80% seed germination. Root and shoot lengths were also reduced in all the test extracts except lemon flower extract against cabbage seeds which showed stimulated shoot growth. It may be concluded that lemon plant produces allelotoxins that can inhibit the growth of other crops in its vicinity. Although lemon flower extract showed the stimulatory effect on cabbage seeds, the detailed confirmatory study is necessary.
... Despite the crude rhizome extracts of kaccholam plant showed no significant effect on chlorophyll content in red chillies, but the extracts evidently exhibit inhibitory effects on the plant growth. A similar study targeting red chillies as the recipient plants conducted by Sahoo et al. [15] using leaf extract of Citrus reticulata found germination inhibition of the recipient plants up to 55%. Previously, phytochemical screening against the leaves extract of C. reticulata has been done and resulted several secondary metabolites allegedly allelopathic such as flavonoids, tannins, steroids, and phenolic compound [16]. ...
Kaempferia galanga L showed an allelopathic clues when intercropping planted with coconut plants, however aspects related to allelochemicals of this plant and their inhibitory or stimulatory properties against other crop plants has not been investigated in earnest. This research was conducted in order to determine whether the crude extracts of kacholam have allelopathic properties, either negative or positive, against red chilies. By using completely randomized design, 25 chilli plantss were grouped into five consist of 5 plants each. Each plant was grown individually in a poly bag containing mixture of soil and compost in a ratio of 2:1. Group 1 is the chillies given 0% (v/v) kacholam extract as the control. Group 2, 3, 4 and 5 are the plants treated with kacholam rhizome extract at a concentration of 25%, 50%, 75% and 100% respectively. After being treated for one week the chillies are harvested and all the study parameters namely plant height, dry weight, and concentration of chlorophyll were assessed. The results showed, plant height of red chillies significantly suppressed by kacholam rhizome extract with a concentration of 50% or higher. The dry weight of red chillies was significantly decreased by treatment of kacholam rhizome extract in all level of concentration. However, crude water extract of kacholam plant rhizome showed no significant effects on the concentration of chlorophyll a as well as chlorophyll b. In conclusion, the crude extract kacholam plant rhizomes contains suppressive allelochemicals and, thus Kaempferia galanga is potential to be used as a negative, instead of positive, allelopathic crops.
Though activities have long ceased, historical mining sites may continue to represent a risk to the environment and human health through long-time leaching processes. This study was undertaken to assess the immediate environmental risk posed by historic metallurgical slags upon contact with litter (Fagus sylvatica leaves, Picea abies needles) and stream water. Further, the contribution of direct slag phase bioweathering was investigated using a soil solution favouring microbial growth (biostimulation) versus aqueous sterile soil extracts. The slags' exposure to Acidithiobacillus thiooxidans mimicked the extremely acidic conditions that will eventually develop under long-term weathering of the sulfidic phases present in the slags (e.g. bornite, chalcopyrite). The risk of metal mobilisation was assessed by means of both bio-chemical leaching experiments (quantification by triple quadrupole inductively coupled plasma mass spectrometry QQQ-ICP-MS) as well as phytotoxicity (Zea mays germination; direct contact and soil pot experiments). Potential metal donor slag phases were identified by scanning electron microscopy (SEM-EDS). It was shown that slags would be categorised as hazardous waste when remaining in contact with the studied weathering solutions. Lead was the most mobile element leaching from slags (up to 86%) and exceeded the legal limits for classification as a non-hazardous waste for all executed treatments. Biostimulation had little effect on Cu leaching (up to 2.6% versus 2.5% for the sterile soil extract, respectively). Litter derived solutions, in contrast, enhanced glass dissolution instead of heavy metal bearing phases. Metal leaching was rapid, raising concerns for peak loads on slag exposure to changing biogeochemical conditions. Extremely acidic conditions and bioleaching by A. thiooxidans were shown to result in metal-enriched leachates (up to 92% of Zn) as well as the lowest germination rate in Zea mays, implying a long term risk by sulphide bioweathering. Five week pot experiments with a soil/slag mixture and Zea mays revealed poor growth in all studied conditions. However, a bacterially derived citric acid was found to improve root and shoot development, possibly due to alleviating the toxic effect of some elements. Due to the observed phytotoxicity, we conclude that the phytoremediation/rehabilitation of slag impacted soils may be limited. The search for a metal tolerant plant species that would be efficient in terms of biomass production and metals uptake is a perspective of this work.
The allelopathic impact of multiple trees was studied on the composition, density and biomass of herbaceous weeds in home gardens of Mizoram, NorthEast India. The weed density in the control was significantly (P<0.05) higher than under the tree species. The understorey weed diversity was in the order of Albizzia procera > Aleurites fordii >Areca catechu > Azadiratcha indica, Gmelina arborea and Toona ciliata > Tectona grandis. No relationship between the light intensity and nutrient status of the soil beneath the tree species with the understorey weed diversity and density depicts less impact of the growth resources on weed vegetation.
Effects of aqueous leaf, bark and seed extracts of two tree species viz. [subabul (Leucaena leucocephala (Lama) de Wit) and teak (Tectona grandis L.)] were tested in bioassay and pot culture on germination, radicle length, growth and yield of maize (Zea mays L.). The leaf extract were more toxic than bark and seed and Leucaena was more inhibitory to germination (P < 0.05) than Tectona. On the contrary, the Tectona growth media was more harmful to growth and yield of maize than Leucaena. The toxic effects of Leucaena followed the order: crushed seeds > leaf litter > soil root zone, while Tectona followed the order : leaf litter > crushed seeds > soil root zone. Thus Leucaena was less harmful tree than Tectona for maize intercropping in agroforestry systems of Mizoram.
Nine volatile oils and six methanol extracts from Ocimum americanum, O. basilicum, O. sanctum, Citrus hystrix, Alpinia galanga, Curcuma zedoaria, Kaempferia parviflora and Zingiber cassumunar were assessed for antimicrobial and antioxidant activities. The volatile oils and extracts were investigated against eight bacteria and three fungi. The results illustrated that O. americanum volatile oil exhibited broad spectrum activity against tested bacteria with the MICs ranging 1.4-3.6 mg/ml and Candida spp. with the MICs ranging from 0.5-0.6 mg/ml. The O. sanctum volatile oil showed a considerable activity against only Candida spp. with the MICs ranging from 0.8-1.4 mg/ml. Interestingly, growth of Mycobacterium phlei was inhibited by the volatiles of O. americanum, C. hystrix peel, and C. zedoaria with MIC of 1.7, 3.5 and 1.2 mg/ml, respectively. For antioxidant activity evaluation, the methanol extracts of C. hystrix (leaf and peel) and K. parviflora had potent antioxidant activity by the radical-scavenging DPPH method with IC50 of 24.6, 66.3 and 61.5 mg/ml, respectively. GC-MS analysis revealed the typical chemical profiles of the volatile oils. The major component showed the characteristics of the volatile oils and was probably responsible for the antimicrobial effect.
The effects of three concentrations of Capsicum leachates on germination, seedling growth, chlorophyll and chlorophyll supply-orientation (precursors for chlorophyll biosynthesis) in Vigna radiata var. NM98 were investigated. Capsicum leachates inhibited the germination of V. radiata seeds and also negatively affected root and shoot growths at 50 or 75%. Two-week old etiolated seedlings of V. radiata were cultured in growth chamber in one-tenth Hoagland culture solution with or without 25, 50 or 75% leachates. Leaves were harvested at 0, 6, 12, 24 and 48h time interval after treatment. The concentrations of chlorophyll and its three biosynthetic porphyrin precursors i.e. proto porphyrin IX (Proto), Mg-proto porphyrin IX (Mg-Proto), and protochlorophyllide (Pchlide) were determined and the mole percent of total porphyrins was calculated. Accumulation of chlorophyll and porphyrin contents was inhibited as the leachate concentrations increased. The mole percent of Mg-Proto affected by the leachate exhibited the same pattern as that of Pchlide and Proto. The data strongly suggests that enzymes responsible for the conversion of Proto to Mg-Proto or Mg-Proto to Pchlide may be the major targets of the leachates causing the significant decrease in chlorophyll contents.
Rhazya stricta Decne., an evergreen poisonous shrub, has invaded large areas of overgrazed rangelands in Saudi Arabia. To understand the mechanism by which this noxious plant spreads, a laboratory experiment was conducted to assess its a1lelopathic potential to the germination of some range plants. Leachates were prepared from fresh and dry foliage of R. stricta. Seeds were germinated in petri dishes moistened with either leachates or tap water. Leachates inhibited germination with fresh foliage leachate being most severe. Complete germination inhibition was observed in Farsetia aegyptia and Pennisetum divisum. Haloxylon salicornicum and Lasiurus scindicus were the least affected. Rate of germination was also significantly reduced. H. salicornicum was the least affected (56 and 25% in presence of dry and fresh leachates respectively), while other species were drastically reduced. Washing and regermination of the remaining non-germinated seeds indicated that seed viability of F. aegyptia and P. divisum may have been lost in presence of leachates. Osmotic effects of leachates may have contributed to germination inhibition in Atriplex halimus, Achillea fragrantissima, L. scindicus and R. stricta. While inhibiting early germination of other species, R. stricta needs enough water to leach water soluble inhibitor present in its seeds which in turn would also be sufficient to overcome osmotic effect of foliage leachate.
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 paper presents the suppressive effect of different concentration of aqueous leaf extracts of Neem (Azadirachta indica ) on some agricultural crops e.g. Cicer arietinum L., Brassica juncea (L.) Czern and Coss; Cucumis sativus L.; Phaseolus mungo L.; Raphanus sativus L.; and Vigna unguiculata (L.) Walp. The experiment was conducted in sterilized petridishes with a photoperiod of 24 hours on an average temperature of 29.5<sup>0</sup>C. The result showed that aqueous leaf extract of Azadirachta indica caused significant inhibitory effect on germination, root and shoot elongation and development of lateral roots of receptor plants. The effect was proportional to the concentrations of the extracts and higher concentration had the stronger inhibitory effect whereas in some cases the lower concentration showed stimulatory effect. The study also revealed that inhibitory effect was much pronounced in root and lateral root development rather than shoot and germination.
Phytotoxins released by the dominant species in a lowland forest showed highest accumulations in their respective stands. The accumulation of such phytotoxins corresponded with the amount of litter produced and its decaying rate. The release of phytotoxins and their activity depended on whether they were free or bound, and on their solubility. Therefore, the phytotoxins in soils were highly variable in amounts from one species stand to another species stand, during the same and different times of the year. The persistent accumulation of phytotoxins from all dominant tree species continues to influence the soil properties around the trees. Fourteen phytotoxins were isolated from the leaf litter and the soil. Seven persistent toxins were quantified in soils under different tree stands at various times of the year. The cycle of release of bound and free phenolics is discussed.
Allelopathy has been increasingly recognized as an important ecological mechanism which interprets plant dominance, succession, formation of plant community and climax vegetation, and crop productivity (Muller, 1966, Muller, 1971, Whittaker and Feeney, 1971; Rice, 1984; Chou, 1987; Putnam and Tang, 1986; Waller, 1987; Chou and Waller, 1923, Chou and Waller, 1989). The allelopathic phenomenon is always related to environmental parameters and cannot be singled out from the environmental complex (Muller, 1974). (Koeppe et al. 1971, Koeppe et al. 1976) demonstrated several cases of allelopathic effects in relation to environmental stresses. (Putnam and Duke 1974) firstly introduced the concept into agricultural practice to select a crop variety with high allelopathic potential in order to lessen the use of herbicide. (Chou et al. 1987, Chou et al. 1989) have elaborated a practical system of pasture—forest intercropping in fields to avoid herbicide application and to lessen the labour cost based on an allelopathic approach. Substantial information concerning the allelopathic study in a subtropical and tropical region such as Taiwan has been accumulated, based primarily on the author’s findings since 1972. In particular, the investigation of the allelopathic mechanism in relation to agriculture productivity in Taiwan has been emphasized due to the unique agricultural situation there. This chapter thus describes the research carried out in Taiwan since 1972.
Laboratory experiments were carried out to assess the allelopathic effect of leaf extracts of Eucalyptus camaldulensis Dehn. and their possible phytotoxicity on germination and growth of Brassica juncea. Cucumis sativus, Phaseolus mungo, Raphanus sativus, Cicer arietinum and Vigna unguiculata. Sterilized petridishes were used with a light period of 24 hours and on an average temperature of 28°C. The effects of different aqueous extracts of leaves were compared with distilled water (control). Aqueous extract of the dry leaves significantly inhibited the germination, vigor and growth rate of seedlings of tested crops compared to green leaves.
Allelochemicals play a great role in managed and natural ecosystems. Apart from plant growth, allelochemicals also may influence nutrient dynamics, mycorrhizae, soil chemical characteristics, and microbial ecology. Synergistic action of various factors may better explain plant growth and distribution in natural systems. The book emphasizes the role of allelochemicals in shaping the structure of plant communities in a broader ecological perspective. Readers will gain a unique perspective on plant allelochemicals research by a multifaceted approach to understand the role of these compounds.
The book addresses the following questions: (1) How do allelochemicals influence different components of the ecosystem in terms of shaping community structure? (2) Why is it difficult to demonstrate interference by allelochemicals (i.e., allelopathy) in a natural system in its entirety? Despite a large amount of existing literature on allelopathy, why are ecologists still skeptical about the existence of allelopathy in nature? (3) Why are there only scarce data on aquatic ecosystems? (4) What role do allelochemicals play in microbial ecology? How does altered soil microbial ecology influence community structure and fate of allelochemicals? (5) What role do allelochemicals play in nutrient dynamics in terms of final influence on plant growth and distribution? (6) How do abiotic and biotic factors of an ecosystem influence the functioning of allelochemicals? (7) What are the main pitfalls in presentation, analysis, and interpretation of allelochemical data?
There is a growing appreciation that population- and ecosystem-based approaches complement each other strongly, and in view of this the concept of allelopathy is now applied effectively to address ecosystem-level questions. The objective of this volume is to discuss the questions above to find out the effect of allelochemicals on structure and function of the ecosystem. Readers will gain a unique perspective on plant allelochemical research through a multifaceted approach to understanding the role of these compounds.
Phytotoxins released by the dominant species in a lowland forest showed highest accumulations in their respective stands. The accumulation of such phytotoxins corresponded with the amount of litter produced and its decaying rate. The release of phytotoxins and their activity depended on whether they were free or bound, and on their solubility. Therefore, the phytotoxins in soils were highly variable in amounts from one species stand to another species stand, during the same and different times of the year. The persistent accumulation of phytotoxins from all dominant tree species continues to influence the soil properties around the trees. Fourteen phytotoxins were isolated from the leaf litter and the soil. Seven persistent toxins were quantified in soils under different tree stands at various times of the year. The cycle of release of bound and free phenolics is discussed.
Allelopathy, originally defined as chemically elicited interactions between plants or fungi, is mediated by many types of compounds with different sites and modes of biochemical action. Although it is possible to measure a generalized effect, it is unlikely that deeper insight into the basic mechanisms of this phenomenon will be obtained until problems are more clearly and specifically delineated. Future work should include identification of the compounds found in specific interactions and their evaluation in bioassay systems that use organisms actually involved in the response. A broader range of compounds and test organisms must be considered, and the biochemical sites and mechanisms of interaction must be evaluated, even for compounds that appear to be inactive. Once active compounds have been identified, their release, movement, uptake, and effects on source and target species in the allelopathic system should be examined. The effects of plant density require additional investigation. Studies in which plants are grown in various combinations and ratios can ultimately provide information about the major sources of allelopathic interaction in communities, the role of allelopathy in succession, and the nature and extent of coadaptation of organisms. Understanding the role of allelopathy in succession will require information about the chemistry and biology of interactions, and a better understanding of the ecological factors involved. Agricultural systems can supply much needed information, as they are similar to natural systems but usually are simpler and better defined. In turn, a better understanding of allelopathy is important in many phases of modern agriculture, especially in the tropics. By attacking allelopathic interactions at several organizational levels, the effects collectively known as allelopathy can be understood, even in complex natural communities. Major advancement in understanding allelopathy will be accomplished only by the combined effort of investigators from many disciplines.
A unique pattern of weed exclusion was found under the canopy ofDelonix regia, which was planted in many places as an ornamental tree in the south of Taiwan. A quadrat method was employed to examine the botanical composition between the area underneathD. regia and its adjacent control grassland. The number of species and coverage of understory species were significantly lower in the area of theD. regia than that of the grassland, indicating the growth of understory species was suppressed byD. regia. A series of aqueous extracts of leaves, flowers, and twigs ofD. regia were bioassayed against three species to determine their phytotoxicity, and the results showed highest inhibition in the flowers. A water-culture experiment indicated the aqueous extract of flowers ofD. regia on two local understory species (Isachne nipponensis andCentella asiatica) inhibited growth of both species by more than 70%. The phytotoxicities of fallen leaves and flowers ofD. regia were not significantly affected by temperature. When the plant material was subjected to temperatures above 70°C, however, phytotoxicity was decreased, indicating that the allelopathic nature ofD. regia could easily be decomposed by fire. By means of paper, thin-layer, and high-performance liquid chromatography, and UV-visible spectrophotometry, responsible phytotoxins present in leaves, flowers, and twigs ofD. regia were identified as 4-hydroxybenzoic, chlorogenic, 3,4-dihydroxybenzoic, gallic, 3,4-dihydroxycinnamic, 3,5-dinitrobenzoic, and L-azetidine-2-carboxylic acids, and 3,4-dihydroxybenzaldehyde. The findings of bioassays and the number and amount of responsible allelopathic compounds found inD. regia are well correlated, thus permitting the conclusion that the exclusion of understory plants under the canopy ofD. regia trees was due primarily to the allelopathic effect of the fallen flower, leaves, and twigs of theD. regia. A possible mechanism of action is discussed.
In a retrospect of my work on thin-layer chromatography, a summary of results and progress is given. Between 1957 and 1967, emphasis lay on the standardisation of the method, on increasing the number of applications in the hydrophilic field and on the extension of the method to the nanogram range. In the second decade, we developed methods for solvent-free extraction of micro amounts in direct combination with thin-layer chromatography, such as the TAS-procedure, thermofractography and the micro-extraction with supercritical gases.Finally, the report describes the prospects for the third decade of thin-layer chromatography and the aim of even greater improvement in matters of detection.
Previous studies have shown that various Eucalyptus species can yield allelopathic chemicals which may
be effective in suppressing understorey vegetation. However, the techniques employed in many studies
do not resemble natural ecological processes. This study used germination of Lolium and growth of
Lolium, Lemna, Eucalyptus and Acacia to test for allelopathy. Extraction techniques mimicked typical
daily rainfall rates upon quantities of foliage, leaf litter and bark litter that are typically encountered
in forests; root leachates were obtained hydroponically; stemflow was obtained following rainfall; soils
were leached with water; and volatiles from leaves were studied in an enclosed chamber. Fresh intact
leaves caused little growth suppression, in contrast to coarsely chopped leaves and extracted leaf essential
oils which were both highly suppressive. Whole leaf litter, shed bark and, especially, stemflow yielded
suppressive leachates. Evaporative concentration of leachates in soils was demonstrated, which
increased their inhibitory effect. It is apparent that allelopathy must be considered in relation to rainfall
and the soil water balance. Decay was shown to reduce the allelopathic effects of leaf and bark litter
leachates but some inhibitory chemicals remained after 5 months. It was concluded that allelopathy is
likely to be a cause of understorey suppression by Eucalyptus species especially in drier climates.
Extract from yuzu fruit peel (Citrus junos Sieb. ex Tanaka) strongly suppressed the germination of lettuce seeds while that from the peel of other citrus fruits such as navel orange (C. sinensis) and lemon (C. limon Burm. f.) had very little or no effect. The highest inhibitory activity was located in the peel followed by the segment but no significant activity was found in the seed extract of yuzu fruit. The effect of yuzu peel extract was tested on a variety of major crops including 38 crop species. Germination of seeds of tomato (Lycopersicon esculentum Mill.), celery (Apium graveolens L. var. dulce) and watercress (Nasturtium officinale R. Br.) was completely blocked by 27.8 mg dry peel equivalent ml-1 of yuzu peel extract, while that of cucumber (Cucumis sativus L.) and pumpkin (Cucurbita moschata [Duch. ex Lam.] Duch. ex Poir.) seeds was not affected at this concentration, showing a broad variation in the sensitivity of crop seeds to the extract. The effectiveness of yuzu peel was also tested on some harmful weeds. The extract inhibited the elongation of both radicle and hypocotyl in summer weed quinoa (Chenopodium quinoa) grown on agar plates. Yuzu peel powder added to the soil was also effective in suppressing the growth of C. quinoa, Sonchus oleraceus L. and Digitaria ciliaris, while it had little effect on the spring weed Alopecurus aequalis Sobol. A strong growth inhibitory activity of yuzu peel was found in the aqueous phase after solvent extraction and most of the activity was recovered in the neutral fraction that passed through cation and anion exchange resins.
IntroductionApparatus and TechniqueApplicationsThin-Layer Ionophoresis and Thin-Layer ElectrophoresisConclusion
The allelopathic effects of Adina cordifolia, Alnus nepalensis, Celtis australis and Prunus cerasoides were tested by growing crops of Eleusine coracana, Glycine max and Hordeum vulgare on top soil, rhizosphere soil from the plantation of these trees, and on field soil either mulched with dry leaves or irrigated with aqueous leaf extracts of the agroforestry tree species. Germination percentage, shoot length, root length and dry matter production and pigment contents of crops were depressed by agroforestry tree crops. Maximum reduction in germination percentage, root-shoot length and dry matter production was obtained with experimental garden soil mulched with dry leaves of trees and by the effect of Adina cordifolia followed by P. cerasoides, H. vulgare proved most susceptible and E. coracana highly resistant to these tree-top interactions.
Aqueous methanol extracts of Citrus junos, C. unshiu and C. hassaku fruit peel inhibited the growth of the roots and hypocotyls of lettuce (Lactuca sativa L.) seedlings. Significant reductions in the root and hypocotyl growth were observed as the extract concentration increased in all bioassays. The inhibitory activity of C. junos extract on the growth of lettuce roots and hypocotyls was about 13- and 24-fold greater than that of C. unshiu and C. hassaku extracts, respectively. The concentration of abscisic acid--D-glucopyranosyl ester (ABA-GE) in fruit peel of C. junos, C. unshiu and C. hassaku was determined since ABA-GE had been found to be a possible cause of the growth inhibitory effect of C. junos. The concentration was 132, 10.6 and 5.0 g g–1 dry weight in C. junos, C. unshiu and C. hassaku fruit peel, respectively. Thus, there was a good correlation between ABA-GE concentrations in C. junos, C. unshiu and C. hassaku fruit peel and the inhibitory activities of their aqueous extracts, which suggests that ABA-GE may be involved in the growth inhibitory effect of C. junos, C. unshiu and C. hassaku fruit peel.
Three limonoids, namely limonin, nomilin and obacunone, were isolated from the seeds of Citrus reticulata [Blanco Coorg Mandarin]. Their structures were confirmed by spectroscopic studies. With 4th instar larvae of mosquito Culex quinquefasciatus, the EC50 for inhibition of adult emergence was 6.31, 26.61 and 59.57 ppm for obacunone, nomilin and limonin, respectively. The pattern of mortality at around the EC50 levels was indicative of moult inhibiting activity. The efficacy of a limonoid enriched fraction was similar to that of limonin, probably due to the high content (70%) of limonin.
Three limonoid glycosides were isolated from Citrus unshiu peels, and their structures were determined based on MS and NMR spectroscopic data as nomilinic acid 17-O-beta-D-glucopyranoside (1), methyl nomilinate 17-O-beta-D-glucopyranoside (2), and obacunone 17-O-beta-D-glucopyranoside (3). In particular, the location of the sugar moiety was clearly determined by the B/E constant linked scan FABMS method. No limonoid glycosides obtained here were found to have antitumor activity in NCI-H292 and EL-4 cell lines.
Interspecific variation in polyphenol production by plants has been interpreted in terms of defense against herbivores. Several recent lines of evidence suggest that polyphenols also influence the pools and fluxes of inorganic and organic soil nutrients. Such effects could have far-ranging consequences for nutrient competition among and between plants and microbes, and for ecosystem nutrient cycling and retention. The significance of polyphenols for nutrient cycling and plant productivity is still uncertain, but it could provide an alternative or complementary explanation for the variability in polyphenol production by plants.
Antibacterial and antifungal activity of ethanolic extract of grapefruit (Citrus paradisi Macf., Rutaceae) seed and pulp was examined against 20 bacterial and 10 yeast strains. The level of antimicrobial effects was established using an in vitro agar assay and standard broth dilution susceptibility test. The contents of 3.92% of total polyphenols and 0.11% of flavonoids were determined spectrometrically in crude ethanolic extract. The presence of flavanones naringin and hesperidin in the extract was confirmed by TLC analysis. Ethanolic extract exibited the strongest antimicrobial effect against Salmonella enteritidis (MIC 2.06%, m/V). Other tested bacteria and yeasts were sensitive to extract concentrations ranging from 4.13% to 16.50% (m/V).
Salvia leucophylla, a shrub observed in coastal south California, produces several volatile monoterpenoids (camphor, 1,8-cineole, beta-pinene, alpha-pinene, and camphene) that potentially act as allelochemicals. The effects of these were examined using Brassica campestris as the test plant. Camphor, 1,8-cineole, and beta-pinene inhibited germination of B. campestris seeds at high concentrations, whereas alpha-pinene and camphene did not. Root growth was inhibited by all five monoterpenoids in a dose-dependent manner, but hypocotyl growth was largely unaffected. The monoterpenoids did not alter the sizes of matured cells in either hypocotyls or roots, indicating that cell expansion is relatively insensitive to these compounds. They did not decrease the mitotic index in the shoot apical region, but specifically lowered mitotic index in the root apical meristem. Moreover, morphological and biochemical analyses on the incorporation of 5-bromo-2'-deoxyuridine into DNA demonstrated that the monoterpenoids inhibit both cell-nuclear and organelle DNA synthesis in the root apical meristem. These results suggest that the monoterpenoids produced by S. leucophylla could interfere with the growth of other plants in its vicinity through inhibition of cell proliferation in the root apical meristem.
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