Susceptibility of Apple Fruit to Botryosphaeria dothidea and Isolate Variation. K. C. Parker, Former Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. T. B. Sutton, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 77:385-389. Accepted for publication 20 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0385.

The susceptibility of apple fruit, cultivar Golden Delicious, to Botryosphaeria dothidea was investigated by inoculating fruit in the orchard three times during the growing seasons of 2 successive yr. Immature and mature fruit were equally susceptible to B. dothidea; both required a 1- to 1.5-mo incubation period before symptom development. The time of infection of apple fruit in the orchard by B. dothidea was investigated by sampling apples at three locations throughout the season and monitoring disease development in the laboratory. This test demonstrated that fruit can become infected within 7 wk of petal fall, even though macroscopic symptoms do not occur until later. Variation in isolate aggressiveness was investigated with five isolates of B. dothidea collected from infected fruit and limb cankers of trees in four locations in North Carolina. Detached apple fruit were inoculated with the five isolates, and fruit sections from the inoculated regions were removed and examined for disease development over 1 mo. All isolates were pathogenic but varied in aggressiveness.