VIEW ARTICLE

Pathogenicity of Phytophthora cactorum Isolates from New York Apple Trees and Other Sources. Herb S. Aldwinckle, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; F. J. Polach(2), W. T. Molin(3), and R. C. Pearson(4). (2)(3)(4)Assistant Professor, Research Assistant, and Research Associate, respectively, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 65:989-994. Accepted for publication 1 April 1975. DOI: 10.1094/Phyto-65-989.

Phytophthora cactorum was isolated from the root crowns of apple trees from two locations in New York State. All trees displayed crown rot symptoms. The isolates were pathogenic to young apple seedlings inoculated with zoospores and also to excised, debarked, apple twigs inoculated with agar plugs bearing mycelium. Differential interaction between apple cultivars and 15 widely distributed isolates of P. cactorum was observed in a twig-inoculation test. Isolates were placed in four groups according to their interactions with six test apple cultivars. The relative susceptibility of 31 important apple cultivars to three P. cactorum isolates was determined.