Characterizing Pathogenesis-related Proteins and Environmental Conditions that Suppress Dollar Spot Infections of Bentgrass

Dollar spot (Clarireedia spp.) infects almost every turfgrass grown in the U.S. but is especially damaging to cool season turfgrasses. Thus, fungicides are needed to control this pathogen during high disease pressure. Due to the heavy reliance on fungicides, dollar spot populations have developed fungicide resistance, demonstrating the need for new effective treatments that substitute for fungicides. As a result, this study investigated the transcriptional differences between highly susceptible creeping bentgrass (Agrostis stolonifera L.) and colonial bentgrass (Agrostis capillaris L.), a species of bentgrass that is more resistant to dollar spot. I hypothesized colonial bentgrass will possess differentially expressed genes critical in pathogen defense between control and inoculated plants that are either unique to its genotype, expressed higher than creeping bentgrass, or have higher constitutive expression in the non-inoculated controls than creeping bentgrass. To test this hypothesis, pots of both bentgrass species were inoculated with Clarireedia jacksonii and then diseased tissue was harvested at 48, 60, 72 , and 96 hours post inoculation (hpi) for RNA sequencing. Additionally, non-inoculated controls were placed in the same conditions and harvested at the 48 hpi and 96 hpi. Our results indicated colonial bentgrass uses 77 potential resistance genes to prevent dollar spot infection that are either unique or have increased expression in comparison to creeping bentgrass.

This study also determined what environmental factors impact the size of dollar spot infection foci. Previous work in our lab demonstrated, in the absence of ultraviolet light B radiation(UVB), dollar spot infection foci were larger and more severe. As a result, I hypothesized that as the dose of UVB increases, the size of dollar spot infection foci will decrease. To test this hypothesis, creeping bentgrass was inoculated with dollar spot, placed in a growth chamber for 24 hours, and then treated with UVB light at either 1x normal sunlight or 2x normal sunlight for seven days. Our results suggest that dollar spot is UVB light-sensitive because UVB treated plants had infection foci that either stayed the same or decreased in size over the course of the experiment. Thus, UVB light plays a key role in limiting the spread of dollar spot on the turfgrass surface, suggesting the possibility of using UV light as a dollar spot treatment.