Rice leaf associated Chryseobacterium species: An untapped antagonistic flavobacterium displays volatile mediated suppression of rice blast disease

Rice phyllosphere-associated pigmented bacteria were characterized and identified as Chryseobacterium based on 16S rRNA gene sequencing and phenotypic fingerprinting by Biolog. Molecular phylogenetic analysis by maximum likelihood method clustered the leaf Chryseobacterium with plant or soil-associated Chryseobacterium taklimakanense (OsEp-PSA33); Chryseobacterium camaliae (OsEnb-ALM-D20, OsEnb-ALM-D11); Chryseobacterium culicis (OsEnb-ALM-C23, OsEp-PPA23, OsEp-PPA6, OsEnb-ALM-D3); and Chryseobacterium endophyticum (OsEnb-ALM-A6, OsEnb-ALM-A22). Activity testing of Chryseobacterium isolates showed excellent antifungal activity with over 80.0 % mycelial growth inhibition of Magnaporthe oryzae. The Chryseobacterium endophyticum OsEnb-ALM-A6 and OsEnb-ALM-A22 showed over 90 % fungal growth inhibition by volatile compounds. Chemical analysis of volatiles emitted by Chryseobacterium indicated the abundance of 2-Ethyl-hexanol; 1-Hexadecene; 2-Hexyl-decanol; Heptanal; Furan-diol; and Octanal. Upon seed or seedling bacterization, Chryseobacterium endophyticum not only triggered altered growth pattern of rice but also suppressed blast disease (40.0 % reduction over mock). qPCR-based transcriptional analysis showed enhanced expression of defense associated OsCEBiP, OsCERK, OsPAD4, OsNPR1.3, and OsFMO1. The volatile mediated antifungal activity and host defense induction by Chryseobacterium can be a potential alternative to fungicide-based blast management.