Epidemiological studies of Microdochium nivale on turfgrass

Studies on Microdochium nivale were conducted to measure; isolate variation, conidial responses, and environmental effects on infection.; The first study compared growth rates of M. nivale isolates from three locations; Washington, (WA) and from two locations within Michigan, [MI (S); (MI (N)]. Cultures were incubated at temperatures of 10, 15 and 20°C for 48 hours and evaluated using digital image analysis. Significant differences in growth among isolates were detected within locations at all temperatures. Growth and variation was greatest at 20°C and least at 10°C. When isolate groups were compared between locations, WA to MI (S) and MI (S) to MI (N), only the MI (S) to MI (N) 20°C comparison differed significantly from one another. No differences were found between locations at either 10 or 15°C. Isolate growth differed at some temperatures both when compared between locations as well as within a single location.; Effects of temperature and time on M. nivale conidial germination and elongation were quantified on Penncross creeping bentgrass leaflets inoculated with a conidial suspension and exposed to temperatures of 12, 20, and 28°C for 2, 4, 8, 12, 16, 20, or 24 h intervals. The percent of germinated conidia and germ tube length was quantified for each temperature over time. Germination plateaus for temperatures were reached by 12 h (20°C), 16 h (28°C) and 20 h (12°C). All temperatures reached statistically similar plateaus in germination rates by 20 h. Germination rates at 20°C were the highest at 4 and 12 h and rates at 12°C were the lowest at 8 and 16 h. Maximum germ tube elongation occurred at 24 h for each temperature when mean length values reached 123.8 mum at 20, 70.8 mum at 28, and 43.4 mum at 12°C. In this study conidial germination and elongation was greatest at 20°C. Separate preliminary studies measured sporodochia on leaves in 6 to 7 d at 20°C, in 11 d at 12°C, and none observed by 25 d at 4°C.; Growth chamber studies and field observations were conducted to determine the effects of air temperature and leaf wetness duration on development of Microdochium patch on turf. Penncross creeping bentgrass plants were inoculated and maintained in growth chambers while exposed to temperatures of 8, 12, 16, and 20°C at leaf wetness durations of 24, 36, 48, and 60 h. Images of diseased plants were measured digitally for percent area infected. The effects of temperature and leaf wetness duration on disease were significant as were some interactions. Disease increased with temperature and leaf wetness duration, the most disease was measured at 20°C, 60 h (46.3%). Analysis of variance and regression analysis determined the relationships among temperature and leaf wetness duration to disease. A polynomial model was developed to help predict Microdochium patch. Observations of disease outbreaks and weather conditions made on a creeping bentgrass green from 2000 to 2003 agree with growth chamber findings and support the model.