Controle biológico de fitopatógenos de solo por meio de isolados de fungos do gênero Trichoderma e sua contribuição no crescimento de plantas

Abstract

This study aimed to select among twelve isolates of the fungus Trichoderma spp. one (s) with the ability for in vivo biocontrol of Sclerotium rolfsii, Rhizoctonia solani and Fusarium oxysporum f.sp. phaseoli (FOP), all soil fungi, in pepper (Capsicum sp.) cultivar "Casca Dura Ikeda”, lettuce (Lactuca sativa L.) cultivar "Regina", and beans (Phaseolus vulgaris L.) cultivar "Alessa", respectively, for occurrence of damping-off or damping-off, and vascular diseases (wilted). Furthermore, the contribution of these isolates in plant growth was evaluated. Three experiments were planned, the first to select in vitro isolate(s) of Trichoderma spp. with antagonist action, using the pairing test, the production of volatile metabolites, and production of non-volatile metabolites, measuring the growth inhibition of pathogens. A second experiment tested, under green-house conditions, the biological control of the used phytopathogens, with applications of inoculants in commercial substrate, each containing inoculums of Trichoderma spp. selected in vitro. The concentration used was of 109 conidia mL-1 suspension, and the pathogens in the inoculums densities that promoted a higher percentage of disease on the host crops. The third study aimed to evaluate the isolate(s) of Trichoderma spp. with ability to promote crop growth, through conventional inoculation in substrate and measuring the variables indicative of plant growth based on biomass production. In the laboratory experiments the pairing test indicated that most of antagonistic isolates were efficient in competition for space and nutrients, when compared to Sclerotium rolfsii and Rhizoctonia solani. The isolated T-12 stood apart, by promoting total reduction of mycelia growth of Rhizoctonia solani, besides it was responsible for declining in the growth of Sclerotium rolfsii of 54.9%, and of 44.8% in Rhizoctonia solani, through production of volatile and nonvolatile metabolites. With respect to the green-house experiments, the biological control of plant pathogens, the isolate T-03 was the most effective in controlling R. solani in lettuce "Regina." There was no antagonist effect with the isolates of Trichoderma spp. on S. rolfsii for bell pepper cultivar "Casca Dura Ikeda". The isolate T-06 reduced the percentage of "wilt" severity caused by FOP in plants of pole beans cultivar "Alessa". In the test of plant growth contribution, there was an effect of seasonality among some isolates of Trichoderma spp. Trichoderma spp. influenced the growth of lettuce cultivar compared to control. In the Brachiaria decumbens Stapf, the growth contribution of isolates was incipient and only a few isolated stood apart contributing to biomass production and in specific conditions.