STABILITY OF MICROSCLEROTIAL INOCULUM OF COLLETOTRICHUM-TRUNCATUM ENCAPSULATED IN WHEAT FLOUR-KAOLIN GRANULES

Maintaining adequate viability of microorganisms in products for bioco ntrol is critically important for commercial reasons. Microsclerotia ( MS) of the mycoherbicide agent, Colletotrichum truncatum, are its hard y, over-wintering fungal structures. Microsclerotial inoculum at 2, 7, and 23 MS/granule were matrix-encapsulated in wheat flour-kaolin gran ules ('Pesta'), in which the flour provided gluten for the matrix and a food base for the fungus. Pesta granules were dried to a water activ ity of 0.18-0.29. After storage for 52 weeks at 25 degrees C, granules containing 7 and 23 MS were 100% viable and granules with 2 MS were 9 5% viable. Granules with 7 MS were 50% viable after 36 weeks at 35 deg rees C, Pesta granules (440 granules/g) with conidial inoculum at 3.3 x 10(5) c.f.u./g were less storage-stable than granules at the 2 MS/gr anule level. At all MS inoculum levels, granules stored for up to 2 ye ars produced 10(8) c.f.u./g in vitro when incubated on water agar. Hig h water activity was detrimental to long-term viability. In the greenh ouse, 7 MS/granule samples controlled 94% of hemp sesbania when incorp orated into the soil pre-planting. The strategy of encapsulation of th e naturally stable C. truncatum MS and drying to a favourable water ac tivity led to excellent shelf-life for a live biocontrol agent.