Ação de Trichoderma spp. contra Rhizoctonia solani Kühn e promoção de crescimento em alface (Lactuca sativa L.)

Abstract

The fungus Rhizoctonia solani is a soil-dwelling pathogen widely distributed in agricultural environments, causing bottom rot, a disease that manifests as damping-off, root rot, and basal rot in lettuce (Lactuca sativa L.). This fungus attacks several other crops and, in addition to having a wide range of hosts, can persist in the soil, thus hindering disease management by conventional methods, which reinforces the need for sustainable control alternatives. Trichoderma, on the other hand, is a genus composed of a number species, many of which with a significant role as biological control agents, since they act through different mechanisms of action (mycoparasitism, antibiosis, competition, resistance induction, and growth promotion). This study aimed to evaluate the potential of Trichoderma spp. isolates maintained in a culture collection for the control of R. solani and the promotion of lettuce growth. To this end, culture pairing methods and the production of organic compounds with antifungal properties were employed in both in vitroand in vivo assays. In paired cultures, isolates CEN1513, CEN1653, CEN1700, and CEN1339 showed the highest inhibition rates of mycelial growth of the pathogen, with average values above 56%. In volatile organic compound (VOC) production assays, in addition to isolating CEN1513, isolates CEN281, CEN1656, and CEN1242 also stood out, with inhibition rates ranging from 79.00% to 82.00%. These, therefore, demonstrated action against the pathogen through the production of VOCs. In tests performed with culture filtrates, the CEN1080 isolate showed 100% inhibition of R. solani mycelial growth, followed by CEN1339 (81.40%) and CEN1700 (80.36%), indicating the presence of high levels of non-volatile organic compounds (NVCs). Even after autoclaving, the filtrates of the CEN1080 isolate showed 78.33% inhibition, demonstrating the thermostability of VCCs released in the culture filtrates. In growth promotion experiments in Murashige and Skoog media, the T. asperelloides CEN1277 and Trichoderma sp. CEN1685 isolates promoted a significant increase in root length, shoot length, and fresh biomass of seedlings. In the greenhouse, the isolates ESALQ-1306, CEN1277, CEN1685, CEN1659, CEN1242, CEN2141, CEN1700, CEN1416, and CEN287 showed the best results in terms of root length and dry weight; the first two also stood out in terms of plant height. In the disease suppression assay, all isolates demonstrated, to varying degrees, the ability to suppress the disease, with ESALQ-1306, CEN288, and CEN1651 standing out in their ability to reduce symptoms. Overall, the results obtained in this work demonstrate the applicability of Trichoderma isolates as a sustainable tool for managing soil diseases.