Biocontrol potential of a Bacillus subtilis strain BJ-1 against the rice blast fungus Magnaporthe oryzae

摘要

The biocontrol strain BJ-1 was isolated from a contaminated Magnaporthe oryzae culture plate and identified as Bacillus subtilis based on morphological characteristics, Biolog Microlog identification and 16S rDNA sequence analysis. The dual culture test showed that BJ-1 has a wide antimicrobial spectrum, and is especially potent against M. oryzae. The culture filtrates of BJ-1 significantly inhibited mycelial growth of M. oryzae P131, caused mycelial disintegration and induced swollen germ tubes. RT-PCR revealed the expressions of seven lipopeptide synthesis genes, encoding surfactin (srfAA and SPAB-ERIB), fengycin (fenB and FENCEA), subtilin (spa and spaS) and bacilysin (BACD) in BJ-1. Application of 1 x 10(8) CFU mL(-1) bacterial cells or 5 culture filtrates of BJ-1 completely suppressed rice blast on detached leaves. In pot experiments, both spray and seed treatments using culture broth provided more than 50 disease suppression on rice blast. Interestingly, rice seeds soaked in culture broth of BJ-1 before planting induced host systemic resistance to inhibit rice blast development and promote plant growth, with disease reduction of over 70, at a similar level as the fungicide tricyclazole. Expressions of two PR genes (OsPR1a and OsPR10) and three genes (OsPAL, OsICS1 and OsAOS2) known to function in salicylate- and jasmonate-dependent defence signalling pathways in rice plants after seed treatment by culture broth of BJ-1 were significantly induced. This is the first description of the use of B. subtilis as a seed treatment for control of rice blast and these results indicate that B. subtilis BJ-1 is a highly promising biocontrol agent for suppression of rice blast disease.