Factors Influencing the Growth of Phomopsis obscurans and Disease Development on Strawberry Leaf and Runner Tissue. Brian C. Eshenaur, Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. R. D. Milholland, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 73:814-819. Accepted for publication 8 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0814.

Six representative isolates of Phomopsis obscurans from strawberry leaves, petioles, and runners were tested at various temperatures for growth and pathogenicity. The optimum temperature for mycelial growth and germ tube elongation for all isolates was 26–32 C. All isolates tested caused symptoms on both leaf and runner tissue; 30 C was the optimum temperature for disease development. Disease severity increased with increasing inoculum concentration and was greatest at 10⁷ conidia per milliliter. Disease development was favored by at least 72 hr of leaf wetness after inoculation. Young leaves and runners were more susceptible to P. obscurans than mature strawberry tissue.