Prevalence and Pathogenicity of Phytophthora spp. from Sour Cherry Trees in Michigan. Anna Bielenin, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing, 48824-1312, and the Institute of Pomology and Floriculture, 96-100 Skierniewice, Poland. A. L. Jones, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing, 48824-1312, and the Institute of Pomology and Floriculture, 96-100 Skierniewice, Poland. Plant Dis. 72:473-476. Accepted for publication 21 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0473.

In 1986 and 1987, Phytophthora megasperma, P. cactorum, P. cryptogea, P. syringae, and P. cambivora were isolated from the margins of necrotic root and crown tissue from dying sour cherry trees in orchards planted on heavy, poorly drained soils. Phytophthora megasperma was recovered from each of the cherry-growing districts of Michigan and was the most prevalent of the five species. In greenhouse tests involving 66 isolates, all five species caused root rot or canker formation on Mahaleb cherry seedlings that were grown in artificially infested potting medium and periodically flooded. Isolates of P. cryptogea and P. cambivora were highly virulent. Isolates of P. megasperma varied widely in their ability to cause root rot. Isolates of P. cactorum caused little root rot, but they caused large cankers on Montmorency scions of grafted trees and on stems of Mahaleb seedlings. Isolates of P. syringae also caused cankers on seedlings. These results indicate that infection by Phytophthora spp is a significant factor in the death and decline of sour cherry trees in Michigan.

Keyword(s): Phytophthora root and crown rot, Prunus cerasus.