USE OF A CHILEAN NATIVE STRAIN ‘SHERWOOD’ OF TRICHODERMA VIRENS ON THE BIOCONTROL OF BOTRYTIS CINEREA IN LETTUCES GROWN BY A FLOAT SYSTEM

The biocontrol activity of the native strain ‘Sherwood’ of Trichoderma virens on Botrytis cinerea was estimated under a lettuce-growing hydroponic float system and compared with the commercial formulation of T. harzianum strain T₃₉ (Trichodex), and the usual fungicide mixture, benomyl + captan. Therefore, butterhead lettuce seedlings, cv. Esmeralda, were grown on a floating system with the Wye nutrient solution under an environmental controlled greenhouse at Panguilemo Experimental Station, Universidad de Talca, Chile. In a completely randomized block design, six treatments with three replications were used, so for each experimental unit, 36 plants were artificially inoculated with 10⁶ conidia ml^-1 of ^{B. cinerea}. Previously, the plants were sprayed with 109 conidia ml-1 of Sherwood strain, Trichodex or benomyl + captan, according to the planned treatments. The incidence of grey rot in lettuce plants was evaluated at harvest time, 40 days after transplanting. In addition, quality parameters like plant height, weight and number of commercial plants were also evaluated. Lettuces treated with Trichoderma virens ‘Sherwood’ showed a significant lower incidence (P<0.01) of gray rot disease and a significant higher percent of commercial plants (P<0.05) than the control ones. The ‘Sherwood’ strain, Trichodex and the fungicide mixture benomyl + captan showed a control activity on B. cinerea, but no significant differences were found among those treatments. Nevertheless, when lettuce was treated with the special mixture between fungicides and the ‘Sherwood’ strain, a significant higher percent (P<0.05) of commercial plants was observed.