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

Abstract

Genetic and functional characteristics of rice leaf endophytic actinobacterial member,Microbacteriumare described. Morphotyping, multilocus sequence analysis and transmission electron microscopy indicated the species identity of the endophytic bacterium, OsEnb-ALM-D18, asMicrobacterium testaceum. The endophyticMicrobacteriumshowed probiotic solubilization of plant nutrients/minerals, produced hydrolytic enzyme/phytohormones, and showed endophytism in rice seedlings. Further, the endophytic colonization byM. testaceumOsEnb-ALM-D18 was confirmed using reporter gene coding for green fluorescence protein.MicrobacteriumOsEnb-ALM-D18 showed volatilome-mediated antibiosis (95.5% mycelial inhibition) onMagnaporthe oryzae. Chemical profiling ofM. testaceumOsEnb-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,M. testaceumaltered 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 withM. testaceum. qPCR-based gene expression analysis showed induction ofOsCERK1,OsPAD4,OsNPR1.3, andOsFMO1 suggestive of endophytic immunocompetence against blast disease. Moreover,M. testaceumOsEnb-ALM-D18 conferred immunocompetence, and antifungal antibiosis can be the future integrated blast management strategy.