Biological Control Of Soil-borne Diseases Research Articles

Biological control of soilborne diseases in organic potato production using hypovirulent strains of Rhizoctonia solani

ABSTRACTSoilborne diseases are persistent problems in potato production and alternative management practices are needed, particularly in organic production, where control options are limited. Selected biocontrol organisms, including two naturally occurring hypovirulent strains of Rhizoctonia solani (Rhs1A1 and Bs69) and a commercially available Bacillus subtilis (GB03), were evaluated, both individually and in combination, for control of soilborne diseases of potato under organic production practices over three field seasons in Maine. Varying rainfall conditions over the 3 years significantly affected crop growth, tuber yield, and disease development. However, multiple biocontrol treatments resulted in significant reductions in black scurf and common scab under a variety of environmental conditions, reducing incidence and severity of each by 15–47%. Most biocontrol treatments reduced black scurf, but only specific treatments reduced common scab and silver scurf (by 15–40% and 16–24%, respectively). Combinations including both a hypovirulent strain and GB03 tended to be the most effective treatments overall. Although tuber yield varied greatly by year, Rhs1A1 and GB03 treatments, as well as combinations, increased yield by 11–37% over all three seasons. Use of hypovirulent R. solani, along with other biocontrol organisms, may provide reductions in soilborne diseases and enhanced yield in organic potato production.

Characterization of Antifungal Volatile Organic Compounds Produced by Bacterial Endophytes against Fusarium oxysporum through GC-MS Analysis

Banana (Musa spp.) is one of the most important fruit crops cultivated throughout the world. Fusarium wilt caused by the fungus, Fusarium oxysporum f. sp. cubense (E.F. Smith) Snyder & Hansen (Foc) causes significant threats to banana production. Endophytic bacteria play a significant role in plant protection against soil borne plant pathogens and promote overall productivity of agricultural ecosystems. Secondary metabolites produced by several species of Bacillus have been found to possess antibacterial or antifungal activity against different isolates of Fusarium oxysporum f. sp. cubense. These were identified by crude tests using agar gel diffusion and GC-MS analysis of the fungal crude extracts. Understanding of the metabolites produced by endophytes is also important in the context of biological control of soil-borne diseases of banana. GC-MS analysis of crude antibiotic extracts of bacterial endophytic isolates viz., GNBS3, PVBS3, NPBS4, KVBS4, BS1, revealed DL-Proline,5 Oxo as the major compound. Having both antifungal and antibacterial activity.

微生物相の制御による病原微生物抑制(環境保全型農業のための微生物利用:複合微生物系における有用微生物の動態と制御,シンポジウム)

微生物相の制御による病原微生物抑制(環境保全型農業のための微生物利用:複合微生物系における有用微生物の動態と制御,シンポジウム)

微生物を利用した土壌病害の防除(環境と土壌微生物,シンポジウム)

微生物を利用した土壌病害の防除(環境と土壌微生物,シンポジウム)

Multifunctionality and diversity of culturable bacterial communities strictly associated with spores of the plant beneficial symbiont Rhizophagus intraradices

Arbuscular Mycorrhizal Fungi (AMF) live in symbiosis with most crop plants and represent essential elements of soil fertility and plant nutrition and productivity, facilitating soil mineral nutrient uptake and protecting plants from biotic and abiotic stresses. These beneficial services may be mediated by the dense and active spore-associated bacterial communities, which sustain diverse functions, such as the promotion of mycorrhizal activity, biological control of soilborne diseases, nitrogen fixation, and the supply of nutrients and growth factors. In this work, we utilised culture-dependent methods to isolate and functionally characterize the microbiota strictly associated to Rhizophagus intraradices spores, and molecularly identified the strains with best potential plant growth promoting (PGP) activities by 16S rDNA sequence analysis. We isolated in pure culture 374 bacterial strains belonging to different functional groups—actinobacteria, spore-forming, chitinolytic and N2-fixing bacteria—and screened 122 strains for their potential PGP activities. The most common PGP trait was represented by P solubilization from phytate (69.7%), followed by siderophore production (65.6%), mineral P solubilization (49.2%) and IAA production (42.6%). About 76% of actinobacteria and 65% of chitinolytic bacteria displayed multiple PGP activities. Nineteen strains with best potential PGP activities, assigned to Sinorhizobium meliloti, Streptomyces spp., Arthrobacter phenanthrenivorans, Nocardiodes albus, Bacillus sp. pumilus group, Fictibacillus barbaricus and Lysinibacillus fusiformis, showed the ability to produce IAA and siderophores and to solubilize P from mineral phosphate and phytate, representing suitable candidates as biocontrol agents, biofertilisers and bioenhancers, in the perspective of targeted management of beneficial symbionts and their associated bacteria in sustainable food production systems.

Biological Control of Soilborne Diseases on Tomato, Potato and Black Pepper by Selected PGPR in the Greenhouse and Field in Vietnam

Bacterial wilt, Fusarium wilt and Foot rot caused by Ralstonia solanacearum, Fusarium oxysporum, and Phytophthora capsici respectively, continue to be severe problems to tomato, potato and black pepper growers in Vietnam. Three bio-products, Bacillus vallismortis EXTN-1 (EXTN-1), Bacillus sp. and Paenibacillus sp. (ESSC) and Bacillus substilis (MFMF) were examined in greenhouse bioassay for the ability to reduce bacterial wilt, fusarium wilt and foot rot disease severity. While these bio-products significantly reduced disease severities, EXTN-1 was the most effective, providing a mean level of disease reduction 80.0 to 90.0% against bacterial wilt, fusarium wilt and foot rot diseases under greenhouse conditions. ESSC and MFMF also significantly reduced fusarium wilt, bacterial wilt and foot rot severity under greenhouse conditions. Bio-product, EXTN-1 with the greatest efficacy under greenhouse condition was tested for the ability to reduce bacterial wilt, fusarium wilt and foot rot under field condition at Song Phuong and Thuong Tin locations in Ha Tay province, Vietnam. Under field condition, EXTN-1 provided a mean level of disease reduction more than 45.0% against all three diseases compared to water treated control. Besides, EXTN-1 treatment increased the yield in tomato fruits 17.3% than water treated control plants.

Crop rotation and tillage systems as a proactive strategy in the control of peanut fungal soilborne diseases

Soil management practices can affect the population dynamics of soil microbial communities. Cultural practices can be adequately combined to benefit natural populations of microorganisms that may have a role in biological control (actinomycetes, Trichoderma spp., and Gliocladium spp.), thus contributing to the management of peanut fungal soilborne diseases in a sustainable manner within ecological boundaries. During six agricultural cycles, rhizosphere soil samples were taken from a field subjected to crop rotation (soybean, peanut, and maize), peanut being under two tillage systems (no till, reduced tillage) with the aim of quantifying populations of soil microorganisms. The incidence of diseases caused by soilborne fungi in peanut was determined at harvest. The highest amount of actinomycetes, Trichoderma spp., and Gliocladium spp. were recorded when maize was the preceding crop. Regarding tillage systems, the populations of the three groups of microorganisms were higher in peanut under no tillage than under reduced tillage. Under these conditions, the lowest incidence of peanut blight (Sclerotinia minor) and root rot (strains of Fusarium solani) was observed, suggesting a possible natural control of peanut soilborne pathogens. The quantification of actinomycetes, Trichoderma spp., and Gliocladium spp. was used as a tool to explore the impacts of different management systems on microbial groups that may be involved in the biological control of soilborne diseases, with the aim of combining those practices that improve native populations of possible beneficial microorganisms. This manipulation can provide sustainable management strategies in the control of soilborne diseases, avoiding the use of artificial inoculations of microorganisms, and reducing agrochemical application.

Quantitative isolation of biocontrol agents Trichoderma spp., Gliocladium spp. and actinomycetes from soil with culture media

Soil biodiversity plays a key role in the sustainability of agriculture systems and indicates the level of health of soil, especially when considering the richness of microorganisms that are involved in biological control of soilborne diseases. Cultural practices may produce changes in soil microflora, which can be quantified through the isolation of target microorganisms. Rhizosphere soil samples were taken from an assay with different crop rotations and tillage systems, and populations of Trichoderma spp., Gliocladium spp. and actinomycetes were quantified in order to select the general and selective culture media that better reflect the changes of these microbial populations in soil. The most efficient medium for the isolation of Trichoderma spp. and Gliocladium spp. was potato dextrose agar modified by the addition of chloramphenicol, streptomycin and rose bengal, and for actinomycetes was Küster medium, with cycloheximide and sodium propionate.

Combined Application of the Biological Product LS213 with Bacillus, Pseudomonas or Chryseobacterium for Growth Promotion and Biological Control of Soil-Borne Diseases in Pepper and Tomato

Recent works suggest that the combination of several PGPRs could be more effective than individual strains as a horticultural product. LS213 is a product formed by a combination of two PGPRs, Bacillus subtilis strain GB03 (a growth-promoting agent), B. amyloliquefaciens strain IN937a (an inducer of systemic resistance) and chitosan. The aim of this work is to establish if the combination of three PGPR, B. licheniformis CECT 5106, Pseudomonas fluorescens CECT 5398 and Chryseobacterium balustinum CECT 5399 with LS213 would have a synergistic effect on growth promotion and biocontrol on tomato and pepper against Fusarium wilt and Rhizoctonia damping off. When individual rhizobacterium and the LS213 were put together, the biometric parameters were higher than with individual rhizobacterium both in tomato and pepper, revealing a synergistic effect on growth promotion, being the most effective combination that of B. licheniformis and LS213. When P. fluorescens CECT 5398 was applied alone, it gave good results, which could be due to the production of siderophores by this strain. Biocontrol results also indicate that those treatments that combined LS213 and each of the bacteria (Treatments: T7 and T8) gave significantly higher percentages of healthy plants for both tomato (T7: 65%) and pepper (T7: 75% and T8: 70%) than the LS213 alone (45% of healthy plants for tomato and 60% for pepper) three weeks after pathogen attack. The effects in pepper were more marked than in tomato. The best treatment in biocontrol was the combination of P. fluorescens and LS213. In summary, the combination of microorganisms gives better results probably due to the different mechanisms used.

Biocontrol of soil-borne diseases and plant growth enhancement in greenhouse soilless mix by the volatile-producing fungus Muscodor albus

The use of the volatile-producing fungus Muscodor albus for the biological control of soil-borne diseases in greenhouse soilless growing mix was investigated. Fresh rye grain culture of M. albus incorporated into Rhizoctonia solani-infested growing mix at a rate of 15 g/L or greater provided complete control of damping-off of broccoli seedlings; restoring seedling emergence to levels similar to the non-infested control without deleterious effect to plant growth. The effect of the treatment was essentially local, suggesting that the volatile compounds associated with disease control moved little in the growing mix. Treatment with M. albus was effective at a range of temperatures, from 4 to 22 °C. The ability of M. albus to control damping-off declined rapidly after its incorporation to the growing mix, suggesting that its activity takes place in the initial hours of treatment. In treated mix, damping-off remained under control regardless of planting time after treatment, suggesting that a biological fumigation had killed R. solani. M. albus also completely controlled root rot of bell pepper caused by Phytophthora capsici. Bell pepper and cosmos showed increased growth when planted in non-infested mix treated with M. albus. Since the sterilization of the growing mix by autoclaving had a similar effect on plant growth, it is hypothesized that M. albus enhances growth by controlling deleterious microorganisms that often contaminate commercial growing mixes.

Suppression of Soilborne Plant Pathogens through Community Evolution of Soil Microorganisms.

A distinct microbial community is established in a given environment as a consequence of the community evolution of individual component microorganisms. According to the Community Theory, microorganisms proliferate not as individual species but as a community in response to changes in the environment, evolving into a biological network that is most suitable for their survival and/or further growth. During this process, individual microorganisms interact and communicate with each other by sharing their limited genetic information in order to exploit available resources. Consequently, a functional community comprising many different species is formed. Such microbial communities are comparable to multi-cellular organisms in many ways, but often too complex to be characterized. Nutrient enrichment is one approach to the study of the functions of these inextricably linked biological networks. For soil microbial communities, amendment with organic matter can be employed to apply selective environmental advantages in order to transfer microbial communities to newly evolved biological consortia with distinctive functions. Many studies have reported that the incorporation of composts or green manures rendered soils suppressive to various soilborne pathogens. Among the pathogens that are controlled effectively are Pythium, Phytophthora, and Rhizoctonia. Soil enrichment with organic matter may be the most fundamental and sustainable approach to the biological control of soilborne diseases.

Plant root-bacterial interactions in biological control of soilborne diseases and potential extension to systemic and foliar diseases

Plant-associated bacteria reside in the rhizosphere, phyllosphere, and inside tissues of healthy plants. This chapter discusses concepts and examples of how naturally occurring and introduced bacteria may contribute to management of soilborne and foliar diseases. Introduced bacteria which have demonstrated biological control activity against soil-borne pathogenic fungi and nematodes include rhizobacteria (root-colonising bacteria) and endophytic bacteria (bacteria isolated from within healthy plant tissues). Recently, some introduced rhizobacteria have been found to enhance plant defences, leading to systemic protection against foliar pathogens upon seed or root-treatments with the rhizobacteria. In these cases, introduction of the rhizobacteria results in reduced damage to multiple pathogens, including viruses, fungi and bacteria. An alternative strategy to the introduction of specific antagonists is the augmentation of existing antagonists in the root environment. This augmentation may result from the use of specific organic amendments, such as chitin, which stimulate populations of antagonists, thereby inducing suppressiveness. Inter-cropping or crop rotation with some tropical legumes, including velvetbean (Mucuna deeringiana), lead to management of phytoparasitic nematodes, partly through stimulation of antagonistic microorganisms. Some biorational nematicides, such as specific botanical aromatic compounds, also appear to induce suppressiveness through alterations in the soil microbial community.

Effect of soil salinity on population structure of fluorescent pseudomonads in spinach rhizosphere

Use of PGPR (plant growth-promoting rhizobacteria) for stimulating plant growth and for the biological control of soil-borne diseases is necessary mainly in fields with intensive cropping. The intensive cultivation systems in horticulture have generally led to soil salinity due tp the high rates of fertilizer application. Therefore, the high concentration of inorganic salts accumulated in the plant rhizosphere is likely to be a factor of salinity stress affecting both roots and root-associated rhizobacteria. In a previous report (Matsuguchi and Sakai 1995), we observed that high salinity of soil had induced a significant decrease in the populations of fluorescent pseudomonads in spinach roots. Furthermore, the adverse effect of high salinity of soil was more pronounced on Pseudomonas fluorescens strains than on Pseudomonas putida strains, resulting in an alteration of the composition of fluorescent pseudomonads in the roots where vP. putida} predominated. The objective of the present study was to determine the effect of soil salinity on the population structure, at the strain level, of fluorescent pseudomonad species colonizing spinach roots.

Biological control of soil-borne diseases with antagonistic bacteria

Biological control of soil-borne diseases with antagonistic bacteria

きっ抗微生物による土壌病害の生物的防除

きっ抗微生物による土壌病害の生物的防除

Development of In Vivo Assays for Prescreening Antagonists ofRhizoctonia solanion Cotton

Prescreens of bacteria for biological control of soilborne diseases traditionally consist of tests for antibiosis in vitro. Two in vivo assays were developed as possible alternative prescreens for selecting candidate biological control agents for preemergence and postemergence damping-off diseases of cotton caused by Rhizoctonia solani. In the «radicle assay,» radicles from surface-disinfested seed were inoculated with R. solani. In the «hypocotyl assay,» excised surface-disinfested hypocotyls were inoculated with the pathogen (...)

Biological control of soil-borne diseases, its aspects and problems

Biological control of soil-borne diseases, its aspects and problems