Effects of Temperature On Growth of Sclerotinia Homoeocarpa.

Dollar spot, caused by Sclerotinia homoeocarpa, is an important disease of most turfgrass species worldwide. S. homoeocarpa was described almost a century ago by F.T. Bennett. However, the basic biology and epidemiology of the pathosystem is still unclear. Four isolates of S. homoeocarpa from WI and 6 isolates from OK were grown on native soils and sand. WI isolates were grown with and without creeping bentgrass (Agrostis stolonifera) debris and incubated at temperatures of 11, 14, 17, 20, 23, 26, 29, 31 and 34°C. OK isolates were grown with creeping bentgrass debris only at temperatures of 15, 20, 25, 30, and 35°C. Radial growth of mycelia was recorded at 24, 48, 72, and 96 hours. Growth for all isolates was most rapid between 17 and 26°C. WI isolates grew best on native silt loam with bentgrass debris. Growth was significantly reduced and highly variable at temperatures below 15°C. These data suggest that S. homoeocarpa is saprophytic, and that higher temperatures (17-26°C) are conducive for growth. Growth and saprophytic ability was also compared to other common soil-borne plant pathogens: Colletotrichum, Rhizoctonia, Curvularia, and Gammanomyces. To assess pathogen aggressiveness, 3 WI isolates and 6 OK isolates were inoculated on live creeping bentgrass incubated at 14, 20, 26 or 34°C. Inoculated plants were covered at night and uncovered during the day to increase overnight humidity and leaf wetness, which is conducive to dollar spot development. Disease severity was assessed every 24 hours for four days. Four days post-inoculation, disease was most severe at 14 and 20°C for all isolates, with average severity as high as 25%.  These initial data suggest that S. homoeocarpa infects creeping bentgrass between 14 and 26^oC.