Biological control of Rhizoctonia solani Kuhn, causing banded leaf and sheath blight of corn (Zea mays L.), with Bacillus subtilis (Ehrenberg) Cohn

Forty-one strains of Bacillus isolates from corn roots collected from different parts of the Philippines were screened in-vitro against R. solani isolates, causing banded leaf and sheath blight (BLSB) in corn. Of these, two Bacillus subtilis strains BR23 and BS100 were found very effective in both laboratory and greenhouse screening tests against 7 virulent R. solani isolates also called from different areas of the country. B. subtilis BR23 coated on corn seeds (IPB Supersweet var.) had no adverse effect on germination and seedling vigor. It also multiplied on the root surfaces of seedlings from the bacteria-coated seeds. The optimum pH for growth of BR23 was pH 6. In laboratory tests for biomass production, it grew best in a medium of brown sugar, coconut water, and yeast extract. In test for bacterial biomass carriers, talc proved to be the best in terms of number of bacteria recovered from the seeds. Laboratory formulated B. subtilis BR23 used as seed treatment had not detrimental effect on corn seed germination and seedling vigor. In microplots artificially infested with a selected highly virulent R. solani isolate (RSC3), seed treatment with the same formulation increased corn grain yield by 27% compared to that of the control captan seed treatment with 14.4%. In microplot test wherein B. subtilis BR23 suspension was sprayed 2 times at 2 weeks interval on the stem of one month old corn plants artificially inoculated at the base with R. solani RSC3, the treatment increased grain yield by 35.72% compared to that of the control fungicide azoxystrobin which increased yield by 29.18%. The studies showed the potential of B. subtilis BR23 for commercialization as a seed treatment or spray formulation for the control of BLSB in corn.