Brachypodium distachyon is a C3 grass that is an attractive model host system for studying pathogenicity of major turfgrass pathogens due to its genetic similarity to many cool-season turfgrasses. Infection assays with two or more isolates of the casual agents of dollar spot, brown patch, and Microdochium patch resulted in compatible interactions with B. distachyon inbred line Bd21-3. The symptoms produced by these pathogens on Bd21-3 closely resembled those observed on the natural turfgrass host (creeping bentgrass), demonstrating that B. distachyon is susceptible to the fungal pathogens that cause dollar spot, brown patch, and Microdochium patch on turfgrasses. The interaction between Sclerotinia homoeocarpa isolates and Brachypodium ecotypes was also investigated. Interestingly, differential responses of these ecotypes to S. homoeocarpa isolates was found, particularly when comparing B. distachyon to B. hybridum ecotypes. Taken together, these findings demonstrate that B. distachyon can be used as a model host system for these turfgrass diseases and leveraged for studies of molecular mechanisms contributing to host resistance.

Dollar spot, caused by Sclerotinia homoeocarpa, is one of the most economically devastating diseases of amenity turfgrasses worldwide. The pathogen is readily isolated from active lesions, but detection from seed, dormant host tissue and other plant debris that may serve as a source of primary inoculum is difficult. A semi-selective medium was developed to enhance isolation of S. homoeocarpa. Various fungicides used on turfgrass, the pH indicator dye bromophenol blue, and two pH levels, were assessed for their effects on, and in the case of bromophenol blue, response to growth of S. homoeocarpa and contaminant fungi frequently isolated from field and seed samples. Amendment of the medium to pH 4 promoted growth of S. homoeocarpa in the absence of fungicides and enhanced pathogen growth relative to contaminant isolates on medium amended with 0.1 μg mL −1 triticonazole or 5 μg mL −1 azoxystrobin. The growth rate of S. homoeocarpa on these three media, as determined by in vitro radial growth assays, was consistent for many isolates representing the majority of S. homoeocarpa vegetative compatibility groups. Isolation efficiency on the pH-amended media was tested against antibiotic-amended potato dextrose agar from field samples and artificially inoculated turfgrass seed. In both cases, the medium amended to pH 4 and containing 5 μg mL −1 azoxystrobin significantly decreased contaminant growth with no adverse effects on recovery of S. homoeocarpa in comparison with antibiotic-amended PDA. The enhanced specificity of this medium will be a useful tool for selective detection of S. homoeocarpa and identification of sources of initial inoculum for dollar spot development.Résumé: La brûlure en plaques, causée par Sclerotinia homoeocarpa, est une des maladies du gazon d'agrément dont les répercussions économiques sont des plus importantes à l'échelle mondiale. L'agent pathogène est facilement isolé à partir de lésions actives, mais la détection à partir de semences, de tissu dormant et d'autres débris végétaux qui peuvent servir de source primaire d'inoculum n'est pas aussi simple. On a développé un milieu semi-sélectif pour mettre en relief l'isolement de S. homoeocarpa. Divers fongicides utilisés sur le gazon, l'indicateur de pH bleu de bromophénol et deux niveaux de pH ont été évalués quant à leurs effets sur S. homoeocarpa et, dans le cas du bleu de bromophénol, quant à la réaction par rapport à sa croissance ainsi qu'aux champignons contaminants fréquemment isolés d'échantillons de sol et de semences. L'amendement du milieu pour obtenir un pH de 4 a stimulé la croissance de S. homoeocarpa en l'absence de fongicides et a favorisé la croissance de l'agent pathogène par rapport aux isolats contaminants se développant sur le milieu amendé avec 0.1 µg mL −1 de triticonazole ou 5 µg mL −1 d'azoxystrobine. Le taux de croissance de S. homoeocarpa sur ces trois milieux, comme défini pas les biotests de croissance radiale in vitro, était uniforme pour plusieurs isolats représentant la majorité des groupes de compatibilité végét...

Pythium root rot (PRR), caused by various Pythium species, is a major disease of creeping bentgrass in the transition zone of the United States. Characterization of various Pythium species associated with PRR was determined by identifying 106 Pythium isolates from samples of symptomatic turfgrass cores. Pathogenicity assays were conducted on post-emergent (7-day old) seedlings and mature (5-week old) creeping bentgrass plants that were inoculated with four different Pythium spp. and incubated at 34 °C/28 °C for 1 to 5 weeks. The results demonstrated that pathogenicity on post-emergent seedlings may not correlate with pathogenicity on mature plants. The sensitivity of various Pythium spp. to ten commercially available fungicides was determined through in vitro mycelial growth assays. Isolates (n = 20) varied in sensitivity to fungicides across and within species of Pythium. Management of PRR was determined through field experiments, revealing that cyazofamid-based treatments were most effective when applied preventatively in the early summer, and were able to reduce disease severity when applied curatively.