FORMULATION OF COLLETOTRICHUM-TRUNCATUM MICROSCLEROTIA FOR IMPROVED BIOCONTROL OF THE WEED HEMP SESBANIA (SESBANIA-EXALTATA)

Submerged cultures of the biocontrol fungus Colletotrichum truncatum p roduce high concentrations of microsclerotia (MS) when grown under spe cific nutritional conditions. Previous studies have shown that MS surv ived drying, remained viable following longterm storage at 4 degrees C , and killed hemp sesbania seedlings when incorporated into potting so il. In this study, dried preparations of C. truncatum MS were encapsul ated in wetted formulations of pregelatinized corn hour pregelatinized cornstarch, or a mixture of the two (1:1). Germination rates of micro sclerotia immediately after formulation and drying were not significan tly different, After storage at 4 degrees C for 18 months, MS germinat ion rates were significantly lower for all formulations compared to no nformulated MS, Dried MS were capable of producing mycelia or spores u pon germination when plated on water agar. After 3 days of growth on N oble agar, the MS-flour formulations produced significantly more conid ia than those made with starch, starch-hour or nonformulated MS. By th e 10th day of incubation, significantly more conidia were produced in formulations containing starch-flour (similar to 10-fold) and flour (s imilar to 50-fold) than in MS starch formulations and nonformulated MS . Bioassays showed that all MS preparations incorporated into potting soil incited disease in emerging hemp sesbania seedlings. A significan tly higher incidence of disease was seen in seedlings grown in potting soil containing flour-formulated MS. These results suggest that corn flour formulations of C. truncatum microsclerotia can be used to incre ase the effectiveness of this bioherbicide for controlling the weed he mp sesbania and that increased conidial production may play a role in improving biocontrol efficacy. (C) 1996 Academic Press, Inc.