SOIL-BORNE FUNGI ACT AS BIOCONTROL AGENTS: THE ROLE OF ANTIFUNGAL METABOLITE PRODUCTION

RODRÍGUEZ M.A.; CABRERA, G.M.; GODEAS, A.M.

Biocontrol: Management, Processes and Challenges

Nova Science Publishers, Inc.

Lugar: Hauppauge NY; Año: 2011;

Specific microorganisms promote plant growth and/or disease control, and this approach is considered an efficient alternative to manage pathogenic fungi. Soils defined as suppressive soils inhibit fungal growth. Suppressive soils are a useful resource for finding biocontrol agents. A fungal strain and its potential as a biocontrol agent must be evaluated as follows: i) identify the antagonistic effects of the strain against target pathogens; ii) elucidate the primary fungistatic mechanisms; and iii) establish the appropriate biocontrol management strategies. In the present chapter, suppressive soils from Buenos Aires were screened to detect antagonist fungal strains against Sclerotinia sclerotiorum. Results indicated suppressiveness was correlated with the fungal community composition, and pathogen response. A high proportion of strains producing antifungal metabolites against S. sclerotiorum were detected from saprotrophic fungi isolated from suppressive soils. Strains of Fusarium oxysporum and, Clonostachys rosea, resulted in the production of antifungal compounds corresponding to secondary metabolites of low molecular weight, which reduced S. sclerotiorum growth and also sclerotia formation. They were two of the most frequent species distributed in suppressive soils. Their metabolites responsible for antifungal activities were isolated and identified. In greenhouse assays, F. oxysporum exhibited a significant (P < 0.05) increase in the number of surviving soybean plants when co-inoculated with S. sclerotiorum, compared with plants inoculated with S. sclerotiorum alone. The metabolite responsible for antifungal activity was identified as cyclosporine A. This compound caused both growth inhibition, and suppression of sclerotia formation at extremely low concentrations, making it a suitable biofungicide. Similarly, an antagonist effect on S. sclerotiorum was demonstrated by the C. rosea strain on soybean and lettuce plants in greenhouse experiments. Two different mechanisms were identified in this strain: peptaibiotic metabolite production, and mycoparasitism activity. The isolated C. rosea strain was reported for first time with antifungal activity against plant pathogens, which could be attributed to peptaibiotics. In summary, in vivo experiments indicated that C. rosea and F. oxysporum are possible biocontrol candidates for S. sclerotiorum. In addition, in vitro assays demonstrated that the strains inhibited other root pathogens, suggesting the high strain potential as active biocontrol agents. The antifungal metabolites characterization provides new lines of research development for the production and use of compounds obtained from microorganism cultures as inhibitors of plant pathogen growth. The selection methods for isolate potential biocontrol agents, the use of soil-borne fungi in disease management programs, and the possible employment of fungal bioactive metabolites as biofungicides are discussed in this chapter.