INFLUENCE OF SHADING ON THE RESPONSE OF TALL FESCUE CULTIVARS TO RHIZOCTONIA-SOLANI AG-1-IA

Isolations from turf samples with brown patch symptoms and pathogenici ty tests indicated that Rhizoctonia solani AG-1 IA was the most import ant pathogen causing brown patch of tall fescue (Festuca arundinacea) in Arkansas in 1992. Ten tall fescue cultivars were evaluated for susc eptibility to R. solani in sun and shade environments. Plants were gro wn in a greenhouse for 4 wk under either full sunlight or colored cell ophane that simulated the quality and quantity of light obtained in th e shade of deciduous tree canopies. Plants were then evaluated for dis ease reaction in growth chambers under similar sun or shade conditions . Shade-grown plants of all 10 cultivars had significantly greater dis ease severity than sun-grown plants (P = 0.05). Safari was consistentl y 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 p lants were placed in the opposite light regime, indicating that the mo rphological and physiological effects of shading, and not the shade en vironment, had a greater influence on brown patch severity. Safari had a low level of endophyte infection, and all other cultivars showed no detectable infection.