Biocontrol of Rhizoctonia solani disease and biostimulant effect by microbial products on bean plants

Abstract

Microbial products containing a mixture of fungi and bacteria (EM Bokashi® 2-fi and EM-5 Sutociu® characterised by plant biostimulant activity), Trichoderma harzianum T22 (biofungicide) and the antagonist fungus Trichoderma sp. TJ40 were tested for efficacy against R. solani disease and for their biostimulant effects on bean plants, in growth chamber experiments, and for their direct effect on the pathogen growth, through in vitro experiments. In growth chamber experiments, EM-5 Sutociu was applied to seed (Sut/Se), substrate (Sut/S) and leaf (Sut/L) many times, EM Bokashi 2-fi to substrare (Bok/S) once and combined with Sut, T22 and TJ40 were applied once to substrate. The pathogen was inoculated to substrate at seeding time (first experiment) or at seedling phase (second experiment). Under our experimental conditions, Bok/S+Sut/S+Sut/L, Sut/S+Sut/L, Sut/Se+Sut/S+Sut/L and T22, in the first experiment, and all treatments, with the exception of Bok/S applied alone in the second experiment, gave significantly disease severity reduction and increase of dry weight and leaf area with respect to the infected control. The TJ40 treatment reduced both disease incidence and disease severity only in the second experiment. In the experiment on the biostimulant effect, T22, Bok/S+Sut/S+Sut/L, Sut/S+Sut/L and Sut/Se+Sut/S+Sut/L showed significantly increases of both dry weight and leaf area. The direct effect of the treatment with T22, TJ40, Bok and Sut on R. solani growth in vitro was studied with two methods, submerged colony (SC) and well diffusion (WD) assays. The pathogen growth was completely inhibited by Trichoderma T22 in both assays, by Trichoderma TJ40 in a range of 80-50 % in SD assay, and 50-30 % in WD assay and slightly inhibited or not inhibited by Bok and Sut.