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Influence of Shading on the Response of Tall Fescue Cultivars to Rhizoctonia solani AG-1IA. P. J. ZARLENGO, Graduate Student, Department of Agronomy, University of Arkansas, Fayetteville 72701. C. S. ROTHROCK, Associate Professor, Department of Plant Pathology, and J. W. KING, Associate Professor, Department of Agronomy, University of Arkansas, Fayetteville 72701. Plant Dis. 78:126-129. Accepted for publication 29 September 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0126.

Isolations from turf samples with brown patch symptoms and pathogenicity tests indicated that Rhizoctonia solani AG-1 IA was the most important pathogen causing brown patch of tall fescue (Festuca arundinacea) in Arkansas in 1992. Ten tall fescue cultivars were evaluated for susceptibility to R. solani in sun and shade environments. Plants were grown in a greenhouse for 4 wk under either full sunlight or colored cellophane that simulated the quality and quantity of light obtained in the shade of deciduous tree canopies. Plants were then evaluated for disease reaction in growth chambers under similar sun or shade conditions. Shade-grown plants of all 10 cultivars had significantly greater disease severity than sun-grown plants (P = 0.05). Safari was consistently one of the most susceptible tall fescue cultivars under shade, while Hubbard 87 and Shenandoah were among the least susceptible under both light regimes. Disease severity was not altered when preconditioned plants were placed in the opposite light regime, indicating that the morphological and physiological effects of shading, and not the shade environment, had a greater influence on brown patch severity. Safari had a low level of endophyte infection, and all other cultivars showed no detectable infection.

Keyword(s): Thanatephorus cucumeris