Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 16, 1999
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 is the formulation of the fungus. In nature, chlamydospores, resting and survival spore structures produced by several species of fungi including Fusarium, are resistant to desiccation and temperature extremes and therefore they can be formulated into dry preparations. Initial work resulted in formulations with poor shelf-life. This work describes various methods used for improving shelf-life of the granular formulation 'C7'. The effect of various additives on shelf-life and secondary spore formation by a mycoherbicidal strain of Fusarium oxysporum is described. The study indicates that modifications and addition of certain substrates result in lower losses in viability during the formulation process, good shelf-life at room temperature and moderate humidity, and abundant secondary chlamydospore formation, criteria important for the mycoherbicide to be successful in a biocontrol project. This research will benefit scientists and industry in the formulation of fungi for practical application as mycoherbicides.
Modifications were investigated to improve various aspects of an inexpensive rice:flour:gluten:clay:oil formulation (C7) of a mycoherbicide, Fusarium oxysporum, strain EN4, that causes vascular wilt in coca (Erythroxylum coca var. coca). Fermentor produced biomass, which contained abundant chlamydospores, was incorporated into various adaptations of C7 and stored at room temperature under moderate (50-60%) and low (0-5%) relative humidities (RH). Whereas the effect of RH on shelf-life was not significant after 4 months of storage, the elimination of oil increased significantly the shelf-life from 3 months to more than 12 months, with final colony-forming-units (CFU) of >10**5/g. The addition of various amendments to C7 such as oil, cotton embryo flour (Pharmamedia), and modified rice flour (MR), and their interactions, affected shelf life considerably. Shelf life was improved by incorporating MR instead of gluten into the formulation. Generally, the ability to form secondary propagules (microconidia, macroconidia) on 1% water agar was not affected by the modifications of C7. However, formation of secondary chlamydospores were significantly improved by incorporating Pharmamedia. This study resulted in the development of a formulation (MRRP7) with improved shelf-life and secondary chlamydospore formation.