FERMENTATION STRATEGIES FOR IMPROVING THE FITNESS OF A BIOHERBICIDE

The commercial development of microbial bioherbicides requires the ava ilability of low-cost production methods, The use of liquid culture fe rmentation is generally considered necessary to achieve this goal. Our strategy for optimizing liquid culture media is based on using define d nutritional conditions. Specific changes are made in the nutritional environment of the medium and the effect of these changes is assessed in terms of propagule yield, efficacy, and stability of the bioherbic idal agent. Liquid culture studies with the fungus Colletotrichum trun catum have demonstrated that nutrition impacts not only spore yield bu t also spore efficacy in controlling the weed hemp sesbania. Nutrition al conditions were identified which suppressed sporulation and promote d the production of high concentrations of C. truncatum microsclerotia in liquid culture. Microsclerotia of C. truncatum (particle size rang e = 180 mu m to 425 mu m) showed promise as bioherbicidal propagules d ue to their stability as a dry preparation and their efficacy in contr olling hemp sesbania when used as a soil amendment, By understanding h ow nutrition impacts propagule formation, yield, efficacy, and stabili ty, rational approaches can be taken to develop submerged culture prod uction methods for microbial biocontrol agents. Breakthroughs in these areas should allow numerous promising bioherbicidal agents to become commercial products.