Biological control of sheath blight of rice with bacterial and fungal antagonists

Abstract

Potential bacterial and fungal antagonists were isolated from rhizosphere soils and soils taken from rice fields. These were screened in vitro for their ability to suppress Rhizoctonia solani on agar medium. One isolate of Pseudomonas fluorescens and one isolate of Bacillus subtilis were selected from one-hundred and twelve isolates of potential bacterial antagonists. One isolate of Trichoderma koningii was selected from sixty-seven isolates of potential fungal antagonists. They were selected for in vivo experiment on the basis of their ability to suppress mycelial growth and sclerotial production.

The selected bacterial and fungal antagonists were tested in vivo in a greenhouse experiment for suppression of sheath blight disease development. Seed treatment, rice root dipping, and plant spraying were used for both single and combined antagonist applications. Better suppression of sheath blight disease development was obtained from seed treatment and plant spraying. The two bacterial antagonist applications gave better sheath blight suppression than the fungal antagonist. Application of individual antagonists was more effective than the combined applications (the concentration of bacterial and fungal antagonists in the combination treatments was 50% of the antagonists applied singly).

Seed treatment and plant spraying were selected as two application methods for a field experiment. Antagonists applied by spraying plants one day before Rhizoctonia solani inoculation gave the best suppression of sheath blight disease development. Both Pseudomonas fluorescens and Bacillus subtilis established colonies on rice seeds, rice roots, and rice stems after application.

Epidemiological data such as temperature and relative humidity should be used to predict the likelihood of Rhizoctonia solani infection so that the effectiveness of antagonist application can be enhanced.