Biological control of white mold (Sclerotinia sclerotiorum) in lettuce using Brazilian Trichoderma spp. strains

Widely consumed by the Brazilian, lettuce has a cultivated area of 35,000 ha. Among the diseases that might infect this crop, white mold causes major concerns for producers. Mold is caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bar. It can lead to losses of up to 100% in lettuce. The objectives of this study were assessment of antagonistic effect of Trichoderma spp. isolates, grown and prepared on rice grain, on white mold of lettuce (S. sclerotiorum). The assay was conducted using 12 Trichoderma spp. isolates, four of which came from at least a year of storage at 4ºC, four from areas with a history of the disease and four from areas without a history of the disease. Both fungi were grown on wet rice grains and only Trichoderma strains was dried and ground to be used in the next assay. The experiment was completely randomized in a factorial 12x2 design (Trichoderma spp. × substrate inoculated or not with S. sclerotiorum) and control plants without any of the fungi. The percentage of survived plants was analyzed using AUDPC, number of leaves, stem diameter, length of root system, fresh and dry weight of shoot and root, and total dry matter. The results showed that all Trichoderma spp. were capable of lettuce growth promotion in the presence and absence of S. sclerotiorum. The isolates that showed the best biocontrol of S. sclerotiorum were TC1.15 and WM-13. To promote growth, the best isolates were UFSMT15.1 and WM-13, suggesting that the latter presents desirable characteristics for biocontrol, including excellent feasibility for large-scale production, good antagonistic activity to S. sclerotiorum and the ability to stimulate growth promotion in lettuce.