Trichoderma spp. no controle de doenças causadas por Rhizoctonia solani KÜHN

Abstract

Lettuce is subject to pest and disease attacks; among the diseases, damping-off and bottom rot, both caused by the fungus Rhizoctonia solani Kuhn. The control of these diseases can be through the cultivation of resistant varieties and, usually, chemical control. However, as an alternative to minimize the impacts of the use of pesticides, there is biological control, within which the fungus of the genus Trichoderma stands out, widespread in the control of plant diseases, in addition to being able to promote plant growth. Given the above, this study aimed to evaluate 31 isolates of Trichoderma spp. in the control of damping-off and bottom rot caused by R. solani and the potential of these isolates to promote the growth of lettuce plants and molecularly identify selected isolates in vitro. The in vitro and in vivo tests were carried out with the curly lettuce cultivars, the organic Crocantela and the conventional Isabela. In an in vitro test, the potential of Trichoderma spp. in inhibiting the mycelial growth of R. solani. Seven Trichoderma isolates inhibited by 100% the mycelial growth of R. solani (INPA 2475, INPA 2478, INPA 2976, INPA 2981, INPA 2983, INPA 2997 and INPA 2991). These isolates were used in the other experiments. In the evaluation of the production of volatile compounds the isolates INPA 2475 and INPA 2478 reduced the average diameter of the colony of R. solani in 31.8% and 52.3%, respectively, in relation to the control. In the in vivo experiments, the incidence of damping-off in lettuce plants and the severity of skirt blight were evaluated. The isolates were not efficient in the control of tipping and bottom rot. The seven isolates of Trichoderma spp. were also evaluated as biostimulants of lettuce plants, evaluating the variables plant height, shoot fresh mass, root fresh mass and root length. The isolates had no effect on plant height. In Isabela, the isolates INPA 2976, INPA 2983 and INPA 2987 were efficient, when compared to the control, in stimulating root growth. The isolates INPA 2976, INPA 2983 and INPA 2987 provided an increase ranging from 115% to 143%; in shoot fresh mass and the isolates INPA 2976 and INPA 2983 provided an increase of 227% and 190%, respectively; in terms of fresh root mass, the increase was 71%. Finally, the pre-selected isolates were molecularly identified, identifying the species Trichoderma spirale (INPA 2991), Trichoderma asperelloides (INPA 2976, INPA 2987), Trichoderma derotheae (INPA 2981), in addition to a possible new species (INPA 2475) which should be studied again.