Direct antagonism overrides induced systemic resistance response by Bacillus subtilis UD1022 against dollar spot pathogen in creeping bentgrass

Abstract

Dollar spot, a major turfgrass disease, poses significant challenges to the turfgrass industry, highlighting the need for sustainable disease management strategies. Plant growth promoting rhizobacteria (PGPR) Bacillus subtilis strain UD1022 (hereafter UD1022) has previously shown ability to inhibit dollar spot pathogen, Clarireedia jacksonii through direct antagonism under in vitro conditions. However, additional investigation is needed to fully understand its role as a biocontrol agent in planta. It is unclear whether UD1022 suppresses dollar spot in creeping bentgrass, and if so, whether the suppression occurs primarily through induced plant defense responses or via direct antagonism. To address these knowledge gaps, we investigate the biocontrol potential of UD1022 against C. jacksonii in creeping bentgrass, focusing on systemic defense responses and direct antagonism mechanisms. Our data showed that plants primed with UD1022 and subsequently inoculated with foliar dollar spot pathogen did not protect plants against the fungal pathogen. In contrast, UD1022 direct application to the leaves with the pathogen led to a 43.6% reduction in disease severity. Gene expression data showed that UD1022 application to roots triggers foliar defense response dependent on jasmonic acid (JA) and salicylic acid (SA) pathways. In addition, plants treated with UD1022 mutants deficient in sporulation, surfactin, and biofilm formation pathways failed to protect plants against the dollar spot pathogen, suggesting the role of these pathways in disease protection and PGPR fitness. Understanding the mechanisms by which PGPR modulate plant immunity could contribute to the development of sustainable turfgrass management approaches.