Use of chitinolytic Bacillus atrophaeus strain S2BC-2 antagonistic to Fusarium spp. for control of rhizome rot of ginger

Abstract

An antagonistic bacillus S2BC-2 isolated from apple rhizosphere soil was identified to be highly chitinolytic on chitinase detection agar. Standard bacteriological tests and sequencing of 16S rRNA, and gyrA and rpoB genes, indicated a taxonomic affiliation of the strain to Bacillus atrophaeus. The strain was studied for its ability to grow and produce chitinase on different substrates. Bacterial cells grown on chitin-containing media showed enhanced growth and chitinase production with increased anti-fungal activity against vascular wilt pathogens. Extracellular proteins of cell-free extracts of media amended with chitin and fungal cell wall contained 4–10 novel polypeptides. In polyhouse (bamboo structures that provide protective shade made of polyvinyl sheet) studies, a chitin-supplemented talc-based formulation of the S2BC-2 challenge inoculated with Fusarium oxysporum f. sp. zingiberi recorded low percent disease indices of 84.9 % and 79.2 % for yellows and rhizome rot, respectively, over the non-bacterised pathogen control. The low disease incidences correlated with 113.3 % maximum rhizome production and 2-fold higher chitinase induction over the pathogen control. In native gel activity assays, upon challenge-inoculation, S2BC-2 expressed more chitinase isoforms than the pathogen control. The results suggest that chitinolytic B. atrophaeus can be used in the biocontrol of rhizome rot of ginger.