Spo0A-dependent antifungal activity of a plant growth promoting rhizobacteria Bacillus subtilis strain UD1022 against the dollar spot pathogen (Clarireedia jacksonii)

Abstract

Dollar spot is an economically important foliar disease of turfgrass caused by Clarireedia spp. Increased use of chemical fungicides for disease management has possible negative effects on the environment and human health. The quest for eco-friendly alternatives to fungicides is driving the development of new biological strategies for managing dollar spot. In the present study, an analysis of antifungal activity of the plant growth promoting rhizobacteria (PGPR) Bacillus subtilis strain UD1022 (hereafter UD1022) and plant health products (PHPs) (Acibenzolar-S-methyl, kelp extract, fosetyl-Al, and trinexapac-ethyl) against Clarireedia jacksonii for control of the turfgrass fungal disease dollar spot was conducted. In vitro assays revealed that UD1022 has significant inhibitory effects against the mycelial growth of C. jacksonii. Of all the treatments, wild type UD1022 and a non-ribosomal peptide mutant (sfp¯) showed potential antagonism against C. jacksonii with inhibition rate of 17.2 % and 18.4%, respectively. Interestingly a Bacillus-derived broad antifungal compound (surfactin) and PHPs showed no direct antagonistic activity against dollar spot pathogen and were statistically like the untreated control. All the mutants of UD1022 except spo0A¯ showed varying but significant inhibition of the fungal pathogen suggesting that spo0A gene may be directly involved in the antagonism against C. jacksonii. Bacterial volatile compounds (BVCs) of UD1022 may not be involved in antagonism as no fungal inhibition was observed in the indirect assay using split petri plates. Filter sterilized cell free lysate (CFL) as well as heat treated CFL of UD1022 bacterial culture did not show any fungal inhibition indicating a primary role of live bacterial cells and not bacterial-derived or secreted compounds in fungal growth inhibition. The results indicate UD1022 to possess the potential to be extended for the biocontrol of dollar spot of turfgrass.