Influence of Isolate, Cultivar, and Heat Stress on Virulence of Rhizoctonia zeae on Tall Fescue
McCall, David Scott
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Rhizoctonia zeae is a common pathogen of tall fescue and other turfgrasses in various regions of the United States. Disease caused by R. zeae typically occurs during hot, humid summer months when conditions are ideal for growth of the fungus but less than ideal for growth of tall fescue. While R. zeae has been reported on turfgrasses in several Mid-Atlantic states, there are no records of this pathogen being present in Virginia. Rhizoctonia isolates were obtained from samples of various turfgrasses exhibiting typical Rhizoctonia disease symptoms in Virginia. Additional isolates were obtained from several other states. All were characterized with respect to species characteristics as well as pathogenicity and virulence on two common cultivars of tall fescue. All isolates were pathogenic on tall fescue but there was some variability in virulence. There was consistently slightly less disease present on Crossfire II than on Kentucky 31. Experiments were also conducted to determine the impact of prior exposure to high air temperatures on the severity of disease. Preliminary data showed that one week of exposure to higher air temperatures caused an initial increase in overall turf quality, but as length of exposure increased the quality of turfgrass declined. Tall fescue plants were subjected to 0, 7, and 35 days of heat stress prior to inoculation with several isolates of R. zeae. No relationship was found between predisposing heat stress and disease severity.
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