Diversity analysis of antagonists from rice-associated bacteria and their application in biocontrol of rice diseases.

AIMS: To understand the diversity, taxonomy and antagonistic potential of rice-associated bacteria, and to discover new bacteria for biocontrol of rice foliar pathogens.

METHODS AND RESULTS: Amplified ribosomal DNA restriction analysis (ARDRA), BOX-PCR and 16S rRNA gene sequence analysis were used to identify the diversity of 203 rice-associated antagonistic bacteria. Eleven potential biocontrol bacteria were used to test their biological control of rice blast in a natural field experiment. Eleven different genera were encountered in five divisions, including Bacilli, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Deinococci. The most prominent genus in all microenvironments was Bacillus (68 x 5%). The efficacy of rice leaf blast biocontrol was 64 x 35% for strain 1Pe2, 57 x 86% for strain 2R37 and 56 x 44% for strain 1Re14.

CONCLUSIONS: Biocontrol data from the field experiments demonstrated no positive correlation between antagonism, physiological characteristics and biocontrol efficacy. There was significant diversity among the rice-associated bacteria isolated from different microenvironments. The most prominent genus of all microenvironments was Bacillus. Brevibacillus brevis strain 1Pe2 and Deinococcus aquaticus strain 1Re14 have good potential for field application and commercial use.

SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first attempt to study the diversity and identification of rice-associated antagonistic bacteria from different microenvironments, and endophytic bacteria Deinococcus aquaticus strain 1Re14, Acidovorax sp. isolate 3Re21 and Brevibacillus brevis strain 1Pe2 are first reported as rice-associated bacteria.