Utilização de Trichoderma spp. no controle de Sclerotinia sclerotiorum (Lib.) de Bary e no crescimento de alface

Abstract

The fungus Sclerotinia sclerotiorum is responsible for significant production losses in lettuce. Because it is a soil fungus, its management is difficult and an alternative, is the use of biological control using species of the genus Trichoderma. Among the many factors that can interfere with the performance of this antagonist, the origin of the isolates and storage are still poorly studied. Little is also known about how Trichoderma spp. isolates obtained from areas with and without a history of white mold disease and stored isolates can affect disease control and growth in lettuce. Thus, the objectives of this study were to quantify populations of species of the genus Trichoderma in soil adjacent to the roots of lettuce in commercial areas with and without a history of white mold, evaluate the growth rate and in vitro antagonism of Trichoderma spp. and S. sclerotiorum, examine the in vivo antagonism of S. sclerotiorum using natives Trichoderma spp. isolates obtained from commercial areas with and without a history of white mold and stored isolates on seedlings and plants of lettuce, and to identify at the level species the isolates of Trichoderma spp. used. Assays were performed in the laboratory of phytopathology at UFSM and in a greenhouse at the town of Santa Maria, RS, Brazil. The parameters evaluated were mycelial growth of the isolates, sporulation of Trichoderma spp., and direct confrontation with the pathogen in vitro. In vivo were evaluated germination, % of surviving plants, disease severity, number of leaves, shoot and root growth dry matter of shoot and root, and total dry matter of lettuce. The results indicate that the population of Trichoderma spp. is different between sampling sites with and without a history of white mold and that Trichoderma spp. isolates from areas with a history of the disease had higher mycelial growth rates when compared to isolates from areas with no history and to isolates stored. In vitro results indicate that highest sporulation, as esporos.mL-1, was presented by UFSMT15.1, UFSMT17 and CP22, and that the isolates stored showed better responses in direct confrontation against S. sclerotiorum. For large scale production, the isolates CP12, CP21, SP13 and SP24 were found to be good alternatives. Trichoderma spp. promoted lettuce seedlings of good quality and a good control of the pathogen, being the isolates SP24 and CP21 able to reduce the severity of damage caused by S. sclerotiorum in lettuce. The isolates UFSMT15.1, TC1.15, ETSR20 and SP13 influencing positively the growth of lettuce in the absence, while UFSMT15.1, SP13 and CP22 showed good results in the presence of the pathogen. However, native isolates of Trichoderma spp. had higher populations on the substrate cultivated with lettuce than the stored isolates. Key words: biological control; white mold; Lactuca sativa L; growth promotion