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Ecology and Epidemiology

Influence of Temperature-Soil Water Status Interactions on the Development of Summer Patch in Poa spp.. K. E. Kackley, Department of Botany and Agronomy, University of Maryland, College Park 20742-5815, Present address: Monsanto Agricultural Company, 3015 Blueford Road, Kensington, MD 20895-2724; A. P. Grybauskas, R. L. Hill, and P. H. Dernoeden. Departments of Botany and Agronomy, University of Maryland, College Park 20742-5815. Phytopathology 80:650-655. Accepted for publication 2 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-650.

Kentucky bluegrass (Poa pratensis) cultivars Aspen and S-21 and annual bluegrass (Poa annua) were treated with live or killed inoculum of Magnaporthe poae and incubated in growth chambers at four temperatures (20, 25, 30, 35 C) and four water-stress conditions corresponding to inferred soil matric potential ranges of >?0.05, ?0.05 to ?0.40, ?0.40 to ?0.80, or ?0.80 to ?1.20 MPa. All plants grown at 35 C died of supraoptimal temperature stress before disease symptoms developed. Disease developed only in plants receiving live inoculum. The area under the disease progress curve for disease incidence was greatest in annual bluegrass at all temperatures, and at 30 C for all grasses. At 20 C, disease incidence and symptom expression were greatest at ?0.05 to ?0.40 MPa. At 25 and 30 C, disease incidence and symptom expression were greatest at >?0.05 MPa. There was a reduction in quality of asymptomatic plants within pots inoculated with live M. poae when compared with plants receiving killed inoculum. Summer patch was most severe in plants growing at supraoptimal temperature stress of 25 or 30 C and high soil moisture. Temperature, but not severe drought stress, appears to be a key factor in summer patch development.