Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 13, 1998
Publication Date: N/A
Interpretive Summary: Some of the major diseases caused by Fusarium species are the vascular wilt diseases caused by formae speciales of Fusarium oxysporum. Recently these vascular wilt pathogens, which are highly specific to their hosts, have been suggested for use as mycoherbicides of weeds, and narcotic plants. One of the major requirements for successful application of a mycoherbicide eis the formulation of the fungus. In nature, chlamydospores, resting and survival spore structures produced by several species of fungi including Fusarium, are resistant to dessication and temperature extremes and therefore they can be formulated into dry preparations. Very little research has been done on formulating chlamydospores of mycoherbicidal strains of Fusarium oxysporum. Current methods use microconidial suspensions as fungal biomass to be incorporated into formulations. This work describes various methods for formulating chlamydospores. The effect of various food substrates on shelf life and secondary spore formation by three mycoherbicidal strains of Fusarium oxysporum is described. The study indicates that most of the formulations meet at least three of the four criteria, such as lower losses in viability during the formulation process, moderate shelf-life at room temperature, abundant secondary chlamydospore formation, and rhizosphere colonization, important for the mycoherbicide to be successful in a biocontrol project. This information will be useful to cooperating agencies and private industry for formulating host-specific mycoherbicides.
Various techniques were studied to formulate mycoherbicidal strains of Fusarium oxysporum causing vascular wilts in coca (Erythroxylum coca var. coca) and in poppy (Papavar somniferum). Biomass abundant in chlamydospores was incorporated into alginate prills, and also into granular formulations such as corn flour:starch, wheat flour:kaolin ("Pesta"), and rice:wheat flour (C6) and rice:wheat gluten (C7) formulation. At room temperature, alginate formulations containing cotton seed flour, soya bean hull fibre, or rice retained greater viable colony forming units that the other formulations. There were no differences between formulations, with the exception of corn cob:alginate and corn flour:starch in the amount of viable secondary propagules they produced. Differences were seen between formulations in their ability to produce secondary chlamydospores. Greater number (log 6.0-7.0) of secondary chlamydospores were produced by C6, C7, Pesta, and alginate-pharmamedia, than by the other formulations (log 4.7-6.0). There were no differences in the ability of C6, rice alginate or the wheat flour:kaolin formulations of F. oxysporum strain EN4-S to colonize the rhizosphere of E. coca seedlings. The study indicates that most of the formulations meet at least three of the four important criteria, such as lower losses in viability during the formulation process, moderate shelf-life at RT, abundant secondary chlamyydospore formation, and rhizosphere colonization.