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Control of seed-borne pathogens on legumes by microbial and other alternative seed treatments
Abstract and Figures
Greenhouse trials were carried out in order to test the efficacy of different seed treatments as alternatives to chemicals
against Colletotrichum lindemuthianum cause of anthracnose on bean and Ascochyta spp. cause of Ascochyta blights on pea, respectively. Resistance inducers, commercially formulated microorganisms, non-formulated
selected strains of different microorganisms (fungi, bacteria and yeasts) and plant extracts were applied as dry or liquid
seed treatments on naturally infested seeds. Seedling emergence and disease incidence and/or severity were recorded. Almost
all seed treatments turned out to be ineffective in controlling the Ascochyta infections, which is in line with the literature
stating that these pathogens are difficult to control. The only alternative treatments that gave some control of Ascochyta spp. were thyme oil and a strain of Clonostachys rosea. The resistance inducers tested successfully controlled infections of bean by C. lindemuthianum. Among the formulated microorganisms, Bacillus subtilis-based formulations provided the best protection from anthracnose. Some strains of Pseudomonas putida, a disease-suppressive, saprophytic strain of Fusarium oxysporum and the mustard powder-based product Tillecur also proved to be effective against bean anthracnose. However, among the resistance
inducers as well as among the other groups, certain agents caused a significant reduction of plant emergence. Different alternative
seed treatments can therefore be used for the control of C. lindemuthianum on bean, while on pea only thyme oil and a strain of Clonostachys rosea showed some effectiveness against Ascochyta spp.
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... lindemuthianum in bean and Ascochyta spp. in pea (Tinivella et al. 2009). Although these treatments are promising, none have been tested adequately in the field. ...
... Biological control agents (BCAs) also offer great potential to control seed-borne disease (Mancini and Romanazzi 2014;Rocha et al. 2019;Tinivella et al. 2009). In blue and Andean lupin, seed treatments with the widely used BCA Bacillus subtilis effectively reduce anthracnose incidence (Mandrik et al. 2007;Yánez-Mendizábal and Falconí 2018). ...
... Streptomyces griseoviridis seed treatment was effective in reducing C. lupini incidence in blue lupin (Mandrik et al. 2007), while the BCA Pseudomonas fluorescens reduced anthracnose disease in common bean (Amin et al. 2014), but not in lupin (Mandrik et al. 2007). The fungus Clonotastachys rosea is widely used as BCA is effective against C. lindemuthianum in bean (Tinivella et al. 2009) and C. acutatum in blue berry (Verma et al. 2006). Trichoderma spp. ...
White lupin (Lupinus albus L.) is a grain legume that is known for its high protein content, nutritional quality, efficient nitrogen fixation and unique ability to form specialized cluster roots that support phosphorus uptake. Despite a severe production decline at the end of the past century, white lupin has seen a recent revival to sustain the demand for plant-based protein and reduce Europes dependency on imported soybean. A major problem in (white) lupin cultivation is anthracnose disease, caused by the globally dispersed, seed- and air-borne fungal pathogen Colletotrichum lupini. This PhD thesis aims to provide insights on how to sustainably control anthracnose disease in white lupin in order to support its re-introduction into European cultivation systems. It describes (i) the genetic diversity, phylogeography and virulence of C. lupini, (ii) the development of a high-throughput phenotyping protocol to reliably screen white lupin germplasm, (iii) a genome-wide association study identifying resistance candidate genes and (iv) the exploration of effective seed treatments to reduce the primary pathogen inoculum. Multi-locus phylogeny and morphological characterization of 39 C. lupini isolates showed that diversity is greater than previously reported, distinguishing a total of six genetic groups and ten distinct morphotypes. Highest diversity was found across the South American Andes, indicating it to be the center of origin of C. lupini. Results reveal that the current pandemic is caused by strains belonging to genetic group II, which are spread globally, and are genetically and morphologically uniform. Group II isolates were shown to be highly aggressive on tested white and Andean lupin accessions. Isolates belonging to the other five genetic groups were mostly found locally and showed distinct virulence patterns on both white and Andean lupin accessions. Despite its uniformity, it was shown that two highly virulent group II isolates from Chile could overcome resistance of elite white lupin breeding material, stressing the need to implement phytosanitary protocols for international seed transports. A reliable high-throughput phenotyping tool was developed to identify anthracnose resistance in white lupin germplasm and study pathogen-host interactions. Phenotyping under controlled conditions, performing stem wound inoculation on seedlings, showed to be applicable for high-throughput and its disease scores strongly correlated with two-year Swiss field disease assessments (r = 0.95) and yield (r = -0.64). Phenotyping a diverse set of 40 white lupin accessions revealed eight accessions with improved resistance to anthracnose, which can be incorporated into white lupin breeding programs. A genome-wide association study (GWAS) was done to dissect the genetic architecture for anthracnose resistance in white lupin. White lupin genotypes, collected from the center of domestication and traditional cultivation regions, were screened for anthracnose resistance and characterized through genotyping-by-sequencing (GBS). GWAS revealed two significant SNPs associated with anthracnose resistance on gene Lalb_Chr05_g0216161, encoding a RING zinc-finger E3 ubiquitin ligase potentially involved in plant immunity. Further validation experiments are now required to confirm involvement in plant resistance. Population analysis showed a remarkably fast linkage disequilibrium (LD) decay, weak population structure and grouping of commercial varieties with landraces, corresponding to the slow domestication history and scarce breeding efforts in white lupin. A total of eleven different seed treatments was tested in field trials in Switzerland between 2018 and 2021 to identify treatments that reduce C. lupini infection levels in white lupin. Treatments consisted of hot water, steam, electron, long term storage, vinegar, plant extracts and biological control agents (BCAs). The BCAs were tested under controlled conditions for potential antagonistic activity against C. lupini during white lupin infection prior to field trials. Results showed that long term storage and vinegar treatments can successfully reduce disease incidence and increase yield to levels similar to those observed for certified seeds. In order to sustainably and effectively control anthracnose disease in white lupin, an integrative approach, including modern breeding efforts, disease prevention strategies and mixed cropping systems, is recommended. Further research is required to increase our understanding on white lupin-C. lupini interaction and to identify genetic regions involved in resistance or virulence, respectively, which could greatly support white lupin breeding. This thesis provides the basis to further explore C. lupini population dynamics, virulence and host-speciation, white lupin resistance mechanisms and sustainable ways to control anthracnose disease in order to further facilitate successful white lupin cultivation.
... Various botanical substances such as essential oils of noni, rosemary pepper (dos Santos et al., 2021), Cinnamomum cassia (Pereira et al., 2022), thyme oil, mustard powder-based product (Tinivella et al., 2009) and Chinese gall (Galla chinensis) (Vogelgsang et al., 2013) have been found effective in suppressing seed borne pathogens in various crops. Bio-priming with the use of various antagonistic microorganisms such as Clonostachys rosea, Bacillus subtilis, Pseudomonas putida, and saprophytic strain of Fusarium oxysporum (Tinivella et al., 2009) against seed borne pathogens Colletotrichum lindemuthianum and Ascochyta spp. ...
... Various botanical substances such as essential oils of noni, rosemary pepper (dos Santos et al., 2021), Cinnamomum cassia (Pereira et al., 2022), thyme oil, mustard powder-based product (Tinivella et al., 2009) and Chinese gall (Galla chinensis) (Vogelgsang et al., 2013) have been found effective in suppressing seed borne pathogens in various crops. Bio-priming with the use of various antagonistic microorganisms such as Clonostachys rosea, Bacillus subtilis, Pseudomonas putida, and saprophytic strain of Fusarium oxysporum (Tinivella et al., 2009) against seed borne pathogens Colletotrichum lindemuthianum and Ascochyta spp. have also been reported. ...
The science of agroecology has evolved to embrace practices and campaigns toward sustainable agriculture and food systems. The pathway seeks to enhance operational and resource use efficiency, to substitute ecologically-detrimental inputs and practices with eco-friendly options and design sustainable agro-ecosystems, and scale these systems through transformative development of alternative food networks leading to sustainable global food system based on participation, locality, fairness and justice. This chapter limits its scope to the scale of farm and agroecosystem in discussing the sustainable agricultural practices. The sustainable crop management and agro-ecosystem design components are categorized into eight set of practices, referred here to as 8-S elements. These elements include: (1) spatial bioengineering, (2) species diversification, (3) seed management, (4) seasonal synchrony, (5) soil management, (6) stress management, (7) systems integration, and (8) socio-economic objectivity. Drawing on the results of long-term studies, meta-analysis and narrative review, the eco-friendly, productive options generating ecosystems services and profitability are discussed under each category. The spatial bioengineering involves adaptive modification of physical and vegetal landscape tailored to the constraints presented by climatic, geographic and soil conditions. The niches thus created can be further diversified with crop species in spatial and temporal patterns. While seed sovereignty allows guided evolution of cultivars on-farm, various eco-friendly seed enhancement measures increase productivity and resource use efficiency. Research findings evidenced how seasonal synchrony of production practices can enhance crop adaptability to stochastic environment. The soil management covers the agro-ecological merits and tradeoffs of conservation tillage and soil productivity enhancement measures. The study findings proved the efficacy of various eco-friendly crop stress management options. Systems integration and socio-economic objectivity are touched upon with the perspective of further on-farm diversification, and policy support and fairness for the adoption of sustainable eco-friendly practices.
... Aerated steam treatment has been highly effective in multiple host pathogen systems (Forsberg et al. 2002;Tinivella et al. 2009;Schaerer 2012) and exhibited an effective management of seed-borne infection of Septoria apiicola in celery, F. moniliforme in sweet corn, C. michiganensis subsp. michiganensis in tomato, and X. campestris in cauliflower . ...
Healthy seeds play an important role in growing a healthy crop. Seed health testing is performed by detecting the presence or absence of insect infestation and seed-borne diseases caused by fungi, bacteria, and viruses. The most detrimental effect of seed-borne pathogens is the contamination of previously disease-free areas and the spread of new diseases. Sowing contaminated or infected seeds not only spreads pathogens but can also reduce yields significantly by 15–90%. Some of the major seed-borne diseases affecting yield in cereals, oilseeds, legumes, and vegetables, particularly in the warm and humid conditions prevailing in the tropical and sub-tropical regions, are blast and brown spot of rice, white tip nematode and ear-cockle in wheat, bacterial leaf blight of rice, downy mildews, smuts, head mould, seedling rots, anthracnose, halo blight, and a number of viral diseases. Hence, detection of seed-borne pathogens, such as fungi (anthracnose, bunt, smut, galls, fungal blights), bacteria (bacterial blights, fruit rots, cankers), viruses (crinkle, mottle, mosaic), and nematodes (galls and white tip), which transmit through infected seed to the main crop, is an important step in the management strategies for seed-borne diseases. Thus, seed health testing forms an essential part of seed certification, phytosanitary certification, and quarantine programmes at national and international levels. Detection of seed-borne/transmitted pathogens is also vital in ensuring the health of the basic stock used for seed production and in maintaining the plant germplasm for future research and product development. Besides the precise and reproducible testing methods, appropriate practices during seed production and post-harvest handling, including seed treatment and storage, are important components of seed health management and sustainable crop protection.
... The use of antagonistic Pseudomonas fluorescens in biological seed treatments has been found to significantly reduce the incidence of bacterial wilt in chilli caused by Burkholderia solanacearum (Umesha et al., 2005). There is some indication that microbial seed treatment preparations, such as Serenade® and FZB24®, both Bacillus subtilis-based products, are as effective as conventional fungicides at controlling anthracnose in bean crops (Tinivella et al., 2009). Pre-harvest application of Bacillus subtilis prevents fumonisin development (Bacon et al., 2001). ...
The most of plant diseases are spread through seeds, which is a serious obstacle to obtain high-quality seeds and higher yield. A tiny embryonic plant called a seed is an effective way to spread plant pathogens to new areas and gives them a way to survive from one growing season to the next. One of the most significant biotic constraints on seed production globally is the presence of seed-borne fungi. It is crucial to maintain the initial infection of seed because it serves as a vehicle for the dispersal and survival of plant pathogens. In this connection a review on many seed multiplication strategies for challenging the maintenance of seed borne diseases have been studied which can give proper information to the farmers, seed growers and seed company whose are involved in seed multiplication programme. The major strategies like Selection of disease free field area, source of seed, seed treatment, sowing practices, rouging, isolation requirement, biological control, chemical control, proper harvesting etc. provide a basis for improving seed as an essential part of seed multiplication. The goal of this review is to educate farmers and seed growers with some significant seed pathogens and management strategies for diseases spread through seeds. As a result, seed growers or farmers can obtain maximum seed yield with better quality by using disease free seed in future.
... The percentage was then transformed into a 0-6 scale to obtain the disease severity index in the leaf, similar to EPPO evaluations for the efficacy evaluation of fungicides [38], where a sporulation of 0% was given a "0" value, a sporulation smaller than 5% a "1" value, a sporulation smaller than 10% a "2" value, a sporulation smaller than 25% a "3" value, a sporulation smaller than 50% a "4" value, a sporulation smaller than 75% a "5" value, and a sporulation higher than 75% a "6" value. Those values were transformed into a disease index using the Townsend-Heuberger formula [39]: where v was the severity degree of infection, i was the highest degree of infection, n was the number of leaves presenting each infection degree, and N was the total amount of analyzed samples. ...
Grapevine, a crop of global economic importance, is annually affected by diseases that can compromise the quality and quantity of the harvest, producing large economic losses. Downy mildew caused by Plasmopara viticola (Berk. & M.A. Curtis) Berl. & de Toni is one of the most important diseases in the vineyard. To fight this pathogen, winegrowers often rely on conventional chemical fungicides or copper-based formulations, whose use is determined to be reduced by the European Commission due to their environmental consequences. Hence, alternative plant protection products (PPP) in grapevine must be considered and studied. In this context, we selected several alternative commercial products, based on basic substances (BS) or low-risk active substances (LRAS), to evaluate their suitability to deal with P. viticola. We measured the preventive activity of the products, both in vitro and in planta, as well as their toxicity against the sporangia and zoospores of the pathogen. Results showed that four commercial products were effective against the pathogen directly and preventively, being composed of approved basic substances, more concretely, chitosan, Equisetum arvense, lecithins, and Salix cortex. Among those, the products composed of lecithins and Salix cortex were the most toxic and active preventively. Therefore, these basic substances should be promoted in the vineyard as an alternative to conventional treatments in order to transition to a more sustainable viticulture.
... The scientific literature points to numerous avenues for plant protection against pathogens by microorganisms or botanical substances applied to seeds (Sharma et al. 2015). However, few studies include more than one model plant in their trials (Mao et al. 1998;Tinivella et al. 2009) or the genetic diversity of the plant species considered (Dubey et al. 2007). Similarly, little attention is paid to pathogen diversity within a species or the synergy of different biotic and abiotic stresses Lamichhane 2015). ...
Plants host a wide range of viruses and microorganisms collectively referred to as the plant microbiota. This chapter outlines the state of knowledge on the diversity of these communities of microorganisms within different plant compartments, including the rhizosphere and the phyllosphere. The ecological processes (selection, diversification, dispersal and ecological drift) involved in the assembly of the plant microbiota are also briefly introduced. Finally in the last section of this chapter, the associations between plant traits and microbiota structure are highlighted with a specific emphasis on plant adaptation to biotic stresses.
... The scientific literature points to numerous avenues for plant protection against pathogens by microorganisms or botanical substances applied to seeds (Sharma et al. 2015). However, few studies include more than one model plant in their trials (Mao et al. 1998;Tinivella et al. 2009) or the genetic diversity of the plant species considered (Dubey et al. 2007). Similarly, little attention is paid to pathogen diversity within a species or the synergy of different biotic and abiotic stresses Lamichhane 2015). ...
This chapter summarizes the state of the art and some key research and innovation perspectives with regard to three topics that are particularly important for biocontrol deployment. The first topic is the use of seeds as targets and/or vectors of biocontrol organisms or substances, enabling seed or plant protection through direct antagonism towards pathogens, plant defence stimulation and manipulation of the seed or plant microbiota. The second topic is formulation of biocontrol organisms and substances, a key activity with high importance to enhance performance of biocontrol products and compatibility with agricultural equipment. The third topic deals with digital tools and agricultural equipment to facilitate the use of biocontrol methods in the field: new equipment tailored for field release of organisms, devices for diagnosing the state of plant, pest or biocontrol agent monitoring, tools for optimizing the positioning and parsimonious use of biocontrol methods, etc.
Currently, chitosan (CHT) is well known for its uses, particularly in veterinary and agricultural fields. However, chitosan's uses suffer greatly due to its extremely solid crystalline structure, it is insoluble at pH levels above or equal to 7. This has sped up the process of derivatizing and depolymerizing it into low molecular weight chitosan (LMWCHT). As a result of its diverse physicochemical as well as biological features which include antibacterial activity, non-toxicity, and biodegradability, LMWCHT has evolved into new biomaterials with extremely complex functions. The most important physicochemical and biological property is antibacterial, which has some degree of industrialization today. CHT and LMWCHT have potential due to the antibacterial and plant resistance-inducing properties when applied in crop production. This study has highlighted the many advantages of chitosan derivatives as well as the most recent studies on low molecular weight chitosan applications in crop development.
Two bacterial strains, Pseudomonas fluorescens L18 and Bacillus subtilis K3 and also five plant extracts Garlic (Allium sativum), Clove (Syzygium aromaticum), Black cumin (Nigella sativa), Thyme (Thymus vulgaris) and Sour pomegranate (Punica granatum) were tested for their efficacy against the fire blight disease of pear caused by the bacterium Erwinia amylovora. The results showed that both bacterial strains had good effect on infected shoots, but the P. fluorescens strain had much better and significant effect than the B. subtilis. This strain protected the shoots by 40% and reduced the disease severity index by 44.2 %, while B. subtilis protected the shoots by 20 % and reduced disease severity by 26 %. The pathogen was affected by all plant extracts but the Garlic extract showed the best effect with (34 mm) inhibition zone and Black cumin that showed the least inhibition zone (10.1 mm). It can be concluded that the investigation of different bacterial strains and herbal extracts can be concerned for control of this disease in future.
Chitosan is a nontoxic, inexpensive, biocompatible, and biodegradable biopolymer obtained by deacetylation of chitin. These properties lead to its application in drug release studies and as a biostimulant and elicitor in plants, able to control numerous diseases on various horticultural commodities. Chitosan can form complexes with a series of heavy metals (elemental nonnutrient ions) because of the presence of amino and hydroxyl groups. This ability can alleviate the phytotoxicity caused by heavy metals in plants, avoiding cellular dysfunction on the shoot and roots.
The bacterial isolates studied, I112, II232 and U410, originated from cabbage roots and were previously selected in a screening for activity as a seed treatment against Pythium ultimum on cucumber and kale. Isolates I112 and II232 were identified as Pseudomonas chlororaphis and P. putida biotype A, respectively, by fatty acid analysis. Isolate U410 could not be identified with this method. Based on partial sequencing of the 16SrDNA, U410 was assigned to the complex Xanthomonas/Stenotrophomonas/Xylella within the γ-subgroup of proteobacteria. On cucumber, seed treatment with isolate U410 was more efficacious against damping-off caused by P. ultimum than with isolates I112 or II232. A brief dip of cucumber seeds into a suspension of isolate U410 resulted in a similar level of control of P. ultimum than treatment for 5, 30 or 120 min. As a seed treatment, none of the three isolates gave statistically significant control of Pythium aphanidermatum on cucumber. Seed treatment of peas with I112 or U410 provided some control of Rhizoctonia solani (efficacy 25/30 %). When applied as a soil drench, isolates I112, II232 and U410 protected cucumber against P. ultimum (efficacy: 24-44 %), and cotton against P. ultimum (efficacy: 30-55 %) and R. solani (efficacy: 23-44 %). A root dip into suspensions of I112 or U410 protected greenhouse and field-grown strawberry against Phytophthora fragariae var. fragariae. The bacteria showed no activity against Phytophthora nicotianae on tomato. In non-sterile but pathogen-free potting media, seed treatment with isolate II232 tended to increase the shoot dry weight of maize and pea. Isolate I112 caused a reduction of the dry weight of maize. Isolate U410, and Bacillus subtilis isolated from the commercial product KODIAK® tended to promote the growth of cucumber and kale. The effects of seed bacterization in the absence of pathogens were, however, difficult to interpret overall, as the above mentioned results on growth promotion or inhibition were either not seen in all experiments or statistically not significant.
The efficacy of seed treatments with bioagent ACM941 (a strain of Clonostachys rosea), its formulated products GB116 and ACM941-Pro, and common fungicides for the control of pea root rot complex were examined in six field trials in western Canada from 1996 to 2000. The effects on seedling emergence, root rot severity, and yield varied among years. In trials 1 and 2 (1996-1997), none of the treatments significantly reduced root rot severity or increased yield. ACM941 + Thiram 75WP was the most effective treatment, increasing emergence by 17.4% and was significantly better than that of the untreated controls. In trials 3 and 4 (1997-1998), Apron FL alone and ACM941 + Apron FL were significantly better than the untreated control, increasing emergence by 6.2 and 7.7%, and yield by 10.8 and 11.5%, respectively. In trials 5 and 6 (1999-2000), ACM941 and GB116 were equally the most effective treatments, increasing emergence by 11.5 and 12.2%, and yield by 8.2 and 6.3%, respectively. These effects were significantly greater than that of the untreated control, but not significantly different from those of Apron FL or Vitaflo-280. ACM941-Pro was developed and tested in 2000 only, and it increased emergence by 17.1% and reduced root rot severity by 29.6%.
The bacteria studied originated from roots of field- or glasshouse-grown cabbage seedlings. Of 26 selected isolates with in vitro activity against Phoma lingam and/or Fusarium culmorum, 23 were identified as fluorescent pseudomonads, with Pseudomonas chlororaphis and Pseudomonas putida Biotype B constituting the largest groups. To evaluate their activity in vivo, bacteria were applied to seeds of cucumber and kale and tested simultaneously in the glasshouse for control of P. ultimum. Of the 144 isolates tested, about 30 % showed activity against P. ultimum on cucumber or kale. In further tests with selected isolates, control of P. ultimum was better and more reliable on cucumber than on kale. The efficacy of Pythium control was lower when the pathogen inoculum was evenly mixed into the potting substrate than when it was applied in a layer, although the infection pressure in pathogen checks was comparable. When the pathogen inoculum was applied in a layer, up to 96 % efficacy was observed on cucumber, equivalent to control with thiram (seed treatment) and propamocarb (soil drench). In two experiments on cucumber in which the Pythium inoculum was mixed into the substrate, the efficacy of the most active isolate was 56 % and 48 %, respectively (propamocarb: 84 %/75 %).
The aim of this study was to further characterise the activity as seed treatments of five actinomycete and four Trichoderma strains that in a previous screening under controlled conditions had shown promising activity against Tilletia tritici. The strains were evaluated under controlled conditions for activity against Fusarium culmorum and Fusarium spp./Septoria nodorum on wheat, and Drechslera graminea and D. teres on barley, and some of them were tested for control of T. tritici in the field. Eleven microbial and four non-microbial, commercially available alternative products, most of them developed and marketed for other uses than seed treatment, were also included in the study, mainly to determine their activity against T. tritici. In the experiments under controlled conditions the strains of Trichoderma failed to reduce seedling infection by the pathogens stated above, and the two strains tested against T. tritici in the field did not protect against bunt. These results indicate that the tested Trichoderma strains are no candidates for further development. None of the actinomycetes reduced net blotch (D. teres), but the strains FZB 53 and W 490 had a significant reducing effect on barley leaf stripe (D. graminea) and seedling blight of wheat caused by F. culmorum and, in case of FZB 53, also on Fusarium spp./S. nodorum. In a year with conditions favouring the development of bunt, FZB 53 and W 490 had also activity against T. tritici in the field. For FZB 53 it could be shown that the level of bunt control depended on resistance of the respective variety, but overall the activity of FZB 53 against bunt was insufficient in that year. Of the commercial B. subtilis products evaluated against T. tritici, FZB 24 and Serenade showed activity under controlled conditions, but not in the field. FZB 24 and Serenade had also some activity against D. teres but not against F. culmorum. Serenade was also effective against D. graminea. In two replicated field experiments, the highest level of bunt control (82 and 94% efficacy) was obtained with the seed treatment product Tillecur. In four experiments under controlled conditions, Tillecur showed also consistent activity (mean: 78% efficacy) against barley leaf stripe. Results obtained with all other commercial products either gave no indication for T. tritici activity at the rates tested, or bunt control in the field was low or inconsistent.
Vermicompost (VC) is a nutritionally rich natural organic fertilizer, which releases nutrients relatively slowly in the soil. It improves quality of the plants along with physical and biological properties of soil, i. e., soil aeration, water-holding capacity and ecological balance of microbial soil biota. Aqueous extracts of vermicompost (AVC) inhibited spore germination of several fungi. They also affected the development of powdery mildews on balsam (Impatiens balsamina) and pea (Pisum sativum) caused by Erysiphe cichoracearum and Erysiphe pisi, respectively, in the field at very low concentrations (0.1-0.5 %). Soil amendment with VC (1-5%) induced synthesis of phenolic acids in pea. Maximum phenolic acids were detected in pea plants treated with 4% VC followed by 3% as compared to control. The induction of phenolic acids in plants was correlated with the degree of resistance in treated as compared to non-treated (control) pea plants. The growth of plants grown in VC-amended soil was much better than the growth of plants raised in non-amended soil.
Strains of Pseudomonas fluorescens were applied to wheat seeds as biological control agents against Gaeumannomyces graminis, the cause of take-all disease. Strain L 18, originally isolated from roots of golf grass at a golf course uninfected with G. graminis, significantly suppressed take-all in both greenhouse and field-grown winter and spring wheat. In the field, suppression of take-all was expressed by there being fewer plants with infected roots for more than 6 months, taller plants, and plants having more and longer ears. L 18 protected wheat plants as effectively as the chemicals did until late in the spring. None of the treatments protected wheat plants throughout the entire growing season.