Microbial Antagonists for the Management of Soil-Borne Plant Diseases

Abstract

The effects of microbial antagonists against soil-borne Fusarium oxysporum f. sp. lycopersici of tomato crop (Solanum lycopersicum L.) were investigated through laboratory and greenhouse tests. Samples of soil were taken from infected cropland and the fungal pathogen was isolated by the normal soil-dilution and soil-culture methods on specific culture media. Trichoderma harzianum, Bacillus subtilis and Pseudomonas fluorescens were considered as candidate antagonistic microorganisms and pathogens were inhibited by dual-culture assays, with percentage inhibition of radial growth (PIRG) of each isolate being calculated. The most effective antagonist(s) were then used individually and in combination in a pathogen-inoculated soil and in a healthy soil without pathogen (pathogen-inoculated soil used as control) in a greenhouse experiment, which was designed as a completely randomized design with six treatments and four replications. The incidence of disease, severity of disease, development of pathogens, proportion of plants surviving and growth parameters were measured during the trial. Analysis of variance (ANOVA) was used to analyze data and Tukey's test was employed at p ≤ 0.05 to separate means of treatments. All three antagonists inhibited radial growth of the pathogen in dual-culture assays and the best PIRG was obtained with Trichoderma harzianum. The combined microbial treatment in the greenhouse trial resulted in the lowest disease incidence and severity, and the highest survival rate of the plants, when compared with the pathogen-inoculated control and all the other antagonist treatments, and was significantly better in all growth parameters. The results of this study show that microbial antagonists, especially when used as a consortium, can be used as an effective and environment friendly management solution for soil borne plant diseases.