Factors affecting pathogenicity of the turfgrass dollar spot pathogen in natural and model hosts

Abstract

Clarireedia sp. (formerly called Sclerotinia homoeocarpa), the fungal pathogen that causes dollar spot of turfgrasses, produces oxalic acid but the role of this toxin in Clarireedia sp. pathogenesis is unknown. In the current study, whole plant inoculation assays were used to evaluate pathogenesis of Clarireedia sp. in various model hosts and investigate the role of oxalic acid in dollar spot disease. These assays revealed that both host endogenous oxalate content and pathogen-produced oxalic acid influence the timing and magnitude of symptom development. In time-course expression analysis, oxalate oxidase and related defense-associated germin-like protein genes in creeping bentgrass showed strong up-regulation starting at 48-72 hpi, indicating that germin-like protein genes are most likely involved in defense following initial contact with the pathogen and demonstrating the importance of oxalic acid in Clarireedia sp. pathogenesis. Overall, the results of these studies suggest that oxalic acid and host endogenous oxalate content are important for pathogenesis by Clarireedia sp. and may be associated with the transition from biotrophy to necrotrophy during host infection.