Rice leaf endophytic Microbacterium testaceum: Antifungal actinobacterium confers immunocompetence against rice blast disease

Abstract

Genetic and functional characteristics of rice leaf endophytic actinobacterial member, <i>Microbacterium</i> are described. Morphotyping, multilocus sequence analysis and transmission electron microscopy indicated the species identity of the endophytic bacterium, OsEnb-ALM-D18, as <i>Microbacterium testaceum</i>. The endophytic <i>Microbacterium</i> showed probiotic solubilization of plant nutrients/minerals, produced hydrolytic enzyme/phytohormones, and showed endophytism in rice seedlings. Further, the endophytic colonization by <i>M. testaceum</i> OsEnb-ALM-D18 was confirmed using reporter gene coding for green fluorescence protein. <i>Microbacterium</i> OsEnb-ALM-D18 showed volatilome-mediated antibiosis (95.5% mycelial inhibition) on <i>Magnaporthe oryzae</i>. Chemical profiling of <i>M. testaceum</i> OsEnb-ALM-D18 volatilome revealed the abundance of 9-Octadecenoic acid, Hexadecanoic acid, 4-Methyl-2-pentanol, and 2,5-Dihydro-thiophene. Upon endobacterization of rice seedlings, <i>M. testaceum</i> altered shoot and root phenotype suggestive of activated defense. Over 80.0% blast disease severity reduction was observed on the susceptible rice cultivar Pusa Basmati-1 upon foliar spray with <i>M. testaceum</i>. qPCR-based gene expression analysis showed induction of <i>Os</i>CERK1, <i>Os</i>PAD4, <i>Os</i>NPR1.3, and <i>Os</i>FMO1 suggestive of endophytic immunocompetence against blast disease. Moreover, <i>M. testaceum</i> OsEnb-ALM-D18 conferred immunocompetence, and antifungal antibiosis can be the future integrated blast management strategy.