Submitted to: World Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 1996
Publication Date: N/A
Interpretive Summary: The fungus Colletotrichum truncatum can kill the weed, hemp sesbania. To effectively apply the fungus to a field, a formulation is needed that is stable in storage. We found that excellent shelf life resulted when the hardy fungal pieces called microsclerotia are encapsulated in granules made with wheat flour and kaolin clay. Shelf life was at least one year at 25 deg C when at least 7 microsclerotia per granule are encapsulated. The granules killed weeds in the greenhouse.
Technical Abstract: Microsclerotia (MS) of the mycoherbicide agent, Colletotrichum truncatum, are its hardy, over-wintering fungal structures. Microsclerotial inoculum at 2, 7, and 23 MS/granule were matrix-encapsulated in wheat flour-kaolin granules ('Pesta'), wherein the flour provided gluten for the matrix and a food base for the fungus. After 52-week storage at 25 deg C, granules containing 7 and 23 MS were 100% viable and granules with 2 MS were 95% viable. Granules with 7 MS were 50% viable after 36 weeks at 35 deg C. Pesta granules (440 granules/g) with conidial inoculum at 3.3 x 10 to the fifth c.f.u./g were less storage-stable than granules at the 2 MS/granule level. At all MS inoculum levels, granules stored for up to 2 years produced 10 to the eighth c.f.u./g in vitro when incubated on water agar. High water activity was detrimental to long-term viability. In the greenhouse, 7 MS/granule samples controlled 94% of hemp sesbania when applied preplant-incorporated in soil. The dual strategy of encapsulation of the naturally stable C. truncatum MS and control of water activity led to excellent shelf life for a living biocontrol agent.