Disease Note.

First Report of Phytophthora cactorum and P. citricola Causing Crown Rot of Fir Species in Michigan. G. C. Adams, Jr., Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Anna Bielenin, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824.. Plant Dis. 72:79. Accepted for publication 28 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0079D.

During 1986, Phytophthora cactorum (Lebert & Cohn) Schroeter and P. citricola Sawada were consistently isolated from the crowns of declining seedlings of Pseudotsuga menziesii (Mirb.) Franco, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr., A. balsamea (L.) Mill., A. procera Rehd., and A. fraseri (Pursh) Poir. in nurseries in the lower peninsula of Michigan. Both pathogens were present in one nursery, but P. cactorum was isolated primarily from P. menziesii and A. procera. whereas P. citricola occurred on A. fraseri and A. balsamea. Both pathogens were isolated from all hosts. The pathogens were present regardless of whether the nursery beds were fumigated before planting or the seedlings originated from direct seeding or transplants, were on raised or unraised beds, or were watered with river or well water. Morphological identification of P. cactorum and P. citricola was verified by comparing electrophoretic patterns of proteins of isolates and reference cultures. Koch's postulates were satisfied using methods of injuring host crowns in saturated soil and surrounding them with inoculum. A. procera and A. balsamea are new hosts for the two Phytophthora spp.