Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/1996
Publication Date: N/A
Interpretive Summary: Hemp sesbania is a weed which can cause yield losses of 20-30% in rice, cotton, and soybean in the Southern United States. At present, registered chemical herbicides are unavailable for the control of hemp sesbania in rice or cotton. When a native fungal pathogen is applied to the soil or growing weeds in the form of spores or fungal clumps called microsclerotia, ,hemp sesbania is infected and killed without harm to the growing crop plants. The development of this fungus as a biological for controlling hemp sesbania is dependent on low-cost production methods for spores or microsclerotia and on effective application methods. We have developed a liquid fermentation method for producing stable microsclerotia of this fungus which can infect and kill hemp sesbania seedlings when incorporated into soil. In this study, we evaluated the benefit of formulating dried microsclerotia with corn starch or corn flour. Results showed that the addition of corn flour to dried microsclerotia improved their ability to infect and kill hemp sesbania seedlings. The use of corn flour to improve effectiveness of microsclerotia against hemp sesbania will reduce the number of microsclerotia required to control this weed, thereby reducing the cost of this bioherbicide to the farmer, while increasing the use of the agricultural commodity, corn flour.
Technical Abstract: Submerged cultures of the biocontrol fungus Colletotrichum truncatum produce high concentrations of microsclerotial (MS) propagules when grown under specific nutritional conditions. Previous studies showed that MS survived drying, remained viable following long term storage at 4 deg C, and killed hemp sesbania seedlings when incorporated into potting soil. In nthis study, dried preparations of C. truncatum MS were encapsulated in wetted formulations of pregelatinized corn flour, pregelatinized corn starch, or a mixture of the two (1:1). Microsclerotia germination rates immediately after formulation were 91% in starch, 93% in starch-flour (1:1), 99% in flour, and 100% for nonformulated microsclerotia. After storage at 4 deg C for 9 months, MS germination rates were 79% in starch, 62% in starch:flour, 89% in flour, and 99% for nonformulated. Dried MS were capable of myceliogenic and sporogenic germination when plated on water agar. After 3 days' growth on Noble agar, MS-flour formulations wer producing significantly more conidia than starch, starch-flour, or nonformulated MS. By the 10th day of incubation, significantly more conidia were produced in formulations containing starch-flour (~ 10 fold) and flour (~ 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 higher incidence of disease was seen in seedlings grown in potting soil containing flour formulated MS. These results suggest that flour formulations of C. truncatum microsclerotia can be used to increase the effectiveness of this bioherbicide for controlling hemp sesbania and that increased conidia production may play a role in improving biocontrol efficacy.