VIEW ARTICLE

Etiology

Phytophthora Root and Crown Rot of Cherry Trees. Srecko M. Mircetich, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616; M. E. Matheron, Agricultural Research Technician, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 66:549-558. Accepted for publication 11 November 1975. DOI: 10.1094/Phyto-66-549.

Phytophthora cambivora, P. megasperma, and P. drechsleri were isolated repeatedly from decayed roots and trunk cankers of dead and dying sweet cherry trees affected with crown and root rot in California. The three Phytophthora spp. were often isolated from the same orchard with a high incidence of dead trees and occasionally from the same individual tree. In artificially infested soil, P. cambivora and P. megasperma induced severe root and crown rot, whereas P. drechsleri caused feeder root necrosis only in Mahaleb and Mazzard rootstocks. The symptoms in artificially inoculated cherry rootstocks were the same as those observed in naturally infected trees in the field. Phytophthora cambivora and P. megasperma were more virulent than P. drechsleri to Mahaleb rootstock. Within 3 months in soil artificially infested with P. cambivora or P. megasperma mortality was higher in 1-year-old Mahaleb than in Mazzard seedlings. In surveyed commercial orchards the incidence of dead trees attributed to Phytophthora root and crown rot ranged from a few to more than 75% of trees affected. Orchards with poorly drained soil and trees on Mahaleb rootstock were more severely affected with Phytophthora crown and root rot than orchards on well-drained soil or trees on Mazzard rootstock. This is the first report implicating P. cambivora, P. megasperma, and P. drechsleri directly in root and crown rot and death of cherry trees in commercial orchards.