VIEW ARTICLE

Phytophthora cinnamomi Root Rot and Stem Canker of Peach Trees. Srecko M. Mircetich, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; H. L. Keil, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:1376-1382. Accepted for publication 7 April 1970. DOI: 10.1094/Phyto-60-1376.

Phytophthora cinnamomi, often accompanied by Pythium spp., was isolated repeatedly from decayed rootlets of peach trees in 17 of 33 sampled orchards in Maryland and Pennsylvania. Isolates of P. cinnamomi from peach or avocado induced necrosis of 85% and 25% of the roots, respectively, in 3 weeks, of 3-month-old peach seedlings growing in infested, aerated nutrient solution. Pythium irregulare, P. vexans, and P. ultimum failed to cause root necrosis in the same tests. In naturally and artificially infested soil, P. cinnamomi in greenhouse experiments produced the same symptoms in Elberta peach seedlings as those observed in infected peach trees in the field. High incidence of P. cinnamomi stem canker and root rot was observed in orchards replanted with peach trees and in peach trees growing on land newly cleared of hardwoods and conifers. Mortality of trees attributed to P. cinnamomi in certain peach orchards with poor soil drainage was as high as 50% in the third growing season. This is the first report demonstrating pathogenicity of P. cinnamomi to peach and implicating the pathogen in root rot of peach trees.