Development of a spore-based formulation of microbial pesticides for control of rice sheath blight

An effective formulated biopesticide for controlling sheath blight in rice was developed using three microbial antagonists (Bacillus megaterium, Bacillus subtilis and Aspergillus niger) isolated from the rice sheath. The efficiency of spore-based formulations of the above microbial antagonists was investigated and their effectiveness in controlling sheath blight was demonstrated. Application of talc-based formulations of individual antagonists and mixtures of the three antagonists as spray treatments or soil applications were effective in reducing the incidence by up to 45% at 27 days after inoculation of the pathogen of sheath blight and increased rice yield. The use of spores of a fungal antagonist (A. niger), in comparison to commonly used bacterial antagonists, is a novel feature of the present study. Optimum sporulation conditions of the antagonists for preparation of spore-based formulations and their commercially desirable features such as the ability to maintain spore viability in storage were also determined. Culturing in the synthetic replacement sporulation medium (SRSM-2) for 72 hours was the most effective for sporulation of the two bacterial antagonists while culturing in potato dextrose broth (PDB) for 7 days was the most effective for sporulation of the fungal antagonist. It was demonstrated that talc-based formulations of all antagonists, either in refrigerated storage (4 degrees C) or at room temperature (28+/-2 degrees C), were able to maintain greater spore viability over a longer period (>6 months) than spore suspensions. In view of the relatively shorter life spans of formulations based on vegetative cells, spore-based formulations have a distinct advantage in achieving longer-lasting control, especially under harsh field conditions.