Seasonal Susceptibility of Mutsu Apples to Pseudomonas syringae pv. papulans. T. J. Burr, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. B. Hurwitz, Research Technician, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Plant Dis. 65:334-336. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-334.

Mutsu apple (Malus pumila) fruits showed increased susceptibility to Pseudomonas syringae pv. papulans (PSP) beginning 2–2.5 wk after petal fall and continuing for 2–4 wk. The period of susceptibility was determined by counting lesions on fruits inoculated in the orchard at weekly intervals from petal fall until late August. Ten isolates of PSP produced typical blister spot symptoms on inoculated Mutsu fruits; no symptoms developed on fruits inoculated with 10 isolates of P. syringae pv. syringae. The apple cultivars Cortland, Delicious, Empire, Golden Delicious, Idared, McIntosh, Mutsu, and Rome Beauty all developed blister spot lesions when inoculated with 10⁸ colony-forming units per milliliter of PSP. The lesions were largest and most abundant on Mutsu; isolating PSP from lesions on other cultivars was often difficult or impossible.