Spray-dried powder of for control of rice sheath blight disease: Formulation protocol and efficacy testing in laboratory and greenhouse

A spray-dried powder containing Bacillus megaterium was developed and tested for control of rice sheath blight disease in the greenhouse. The formulation consisted of 20 ml of an endospore suspension of B. megaterium, 20% w/v of skim milk powder and 1.25% w/v of polyvinyl pyrrolidone k-90, that were mixed and spray dried at 120 °C. The powder displayed good physical characteristics, such as a low-moisture content and a high solubility in water. Bacterial viability in the powder was 3.5±0.1 × 1011 cfu/g after production and remained relatively stable (at 2.2±0.1 × 1010 cfu/g) after 12 months of storage at room temperature. In the laboratory, a 0.1% (w/v) aqueous solution of the formulation was effective in inhibiting the mycelia growth of Rhizoctonia solani (98.5±0.1% inhibition). Under greenhouse conditions, a 0.1% (w/v) aqueous solution applied by either spraying 1 day before inoculating R. solani or spraying 1, 7 and 15 days after inoculation of rice plants with R. solani was more effective in suppressing sheath blight disease than the blank formulation but was less effective than a chemical fungicide control