VIEW ARTICLE

Etiology

Pathogenicity and Relative Virulence of Seven Phytophthora spp. on Mahaleb and Mazzard Cherry. W. F. Wilcox, Former graduate research assistant, U.S. Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; S. M. Mircetich, research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 75:221-226. Accepted for publication 21 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-221.

Isolates of Phytophthora cryptogea, P. cambivora, and P. megasperma from cherry, isolates of P. cinnamomi and P. citricola from walnut, and an isolate of P. cryptogea from safflower individually caused 88- 100% root rot and 27- 100% crown rot on Mahaleb cherry seedlings that were grown for 15 wk in artificially infested UC mix and periodically flooded. In contrast, cherry isolates of P. drechsleri and an unidentified Phytophthora sp. caused 62 and 41% root rot, respectively, but caused no crown rot under the same conditions. Mazzard cherry seedlings frequently appeared less susceptible than Mahaleb seedlings to root and crown rot, although this varied with the Phytophthora species involved. Mazzard appeared to be significantly more resistant than Mahaleb to both root rot and crown rot caused by P. cambivora, P. megasperma, and the safflower isolate of P. cryptogea, and to crown rot caused by P. cinnamomi and P. citricola. However, Mazzard roots appeared nearly as susceptible as Mahaleb roots to the latter two Phytophthora spp., and roots of both cherry species appeared moderately susceptible to P. drechsleri and the unidentified Phytophthora sp. Roots and crowns of Mazzard also appeared as highly susceptible as Mahaleb to the cherry isolate of P. cryptogea. This is believed to be the first report experimentally implicating P. cryptogea as a pathogen of a commercial stone fruit tree species in the United States.