Temperature and Osmotic Potential Effects onPhialophora graminicolaand Other Fungi Associated with Patch Diseases ofPoa pratensis

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Abstract
Phialophora graminicola and Leptosphaeria korrae cause patch diseases in Kentucky bluegrass turfs. Fusarium crookwellense is also commonly associated with these diseases. Temperature and osmotic potential effects on growth and pathogenicity of isolates of these fungi from the United States were unknown. Maximum growth rates for P. graminicola, L. korrae, and F. crookwellense occurred in vitro at 28-31, 14-28, and 21-32 C, respectively, and at osmotic potentials >-0.3, >-1.5 and from -0.2 to -4.0 MPa, respectively. P. graminicola grew along rhizomes and through field-produced sod at rates up to 2 cm/wk at 21-29 C, but grew very slowly through sod and on rhizomes at 14 C. Rapid necrosis of colonized plants occurred only at 29 C and, through a system of elevation in the incubation temperatures, this property was used to assay the extent of the pathogen''s growth through sods at lower temperatures. Susceptibility of plants to P. graminicola was pronounced when plants were mowed at 2-cm height compared to being unmowed. L. korrae colonized roots but did not affect plant health under the conditions examined in this study. F. crookwellense thoroughly colonized and halted further growth by cultures of the other fungi on agar medium, but did not contribute to progress of disease caused by P. graminicola, or to symptom expression on plants colonized by L. korrae. Field conditions in which growth of the ectotrophic pathogens are most likely to occur are discussed with respect to conditions associated with the first appearance of disease symptoms.