Effects of biocontrol Bacillus sp. strain D5 on the pathogenic Fusarium oxysporum R1 at the microscopic and molecular level in Crocus sativus L. (saffron) corm

Corm rot of saffron caused by Fusarium oxysporum is a major threat to saffron cultivation the world over. To minimize the ill effects of chemical fungicides, attention has been shifted to the use of biocontrol agents for disease management in a sustainable way. In saffron, various biocontrol agents against corm rot disease have been reported and characterized but no study has been done so far to understand their interaction at the molecular level. The present study was conducted to unravel the mechanism of action of an already characterized native biocontrol agent i.e. Bacillus sp. strain D5 (Bar D5) against Fusarium oxsporum R1 (Fox R1) in the saffron corm. The growth inhibition of Fox R1 was observed in-vitro and in-planta (saffron corm) by real time imaging. Bacillus sp. strain D5 reduced Fox R1 load in infected corms by 50% as quantified by q-PCR and the colony-forming unit method. Comparative transcriptome analysis revealed up-regulation and down-regulation of various Fox R1 genes in presence of Bar D5. The genes related to carbon metabolism, cell wall & membrane synthesis, and growth of Fox R1 were significantly down-regulated in Bar D5 primed and Fox R1 inoculated corms as compared to only Fox R1 inoculated corms.