Brachypodium: Exploration for Use As a Model Host for Fungal Pathogens of Turfgrasses.

Dollar spot, brown patch, and Microdochium patch are three of the most economically devastating fungal diseases of amenity turfgrasses worldwide. Management of these diseases is generally achieved through frequent fungicide applications. Disease resistant turfgrass cultivars are a viable management alternative, but progress in this realm is hampered by limited understanding of how turfgrass pathogens interact with their hosts at the molecular and physiological levels. Brachypodium distachyon is a C3 grass with an assortment of genetic resources and, due its genetic similarity to many cool-season turfgrasses, is an attractive model system for studying host-pathogen interactions in major turfgrass pathosystems. The aims of this study were i) to determine host status of the B. distachyon inbred line Bd 21-3 to three major fungal turfgrass pathogens and ii) to evaluate natural variation of Brachypodium sp. ecotypes in response to S. homoeocarpa isolates. Infection assays with two or more isolates of the casual agents of dollar spot, brown patch, and Microdochium patch resulted in compatible interactions with Bd 21-3.  The symptoms produced by these pathogens on Bd 21-3 closely resembled those observed on the natural turfgrass hosts. Histological studies of Bd 21-3 infection by S. homoeocarpa also revealed colonization similar to that observed on creeping bentgrass, including formation of appressoria and penetration through stomata. Brachypodium sp. natural ecotypes differed in susceptibility to S. homoeocarpa isolates but no ecotype by isolate interaction was detected, indicating a lack of race-specific interactions, in congruence with previous reports from turfgrass systems. These findings demonstrate that B. distachyon is a suitable model host for turfgrass diseases and that differences in susceptibility of Brachypodium sp. ecotypes to S. homoeocarpa can be leveraged to better understand physiological and molecular components of host resistance to dollar spot.