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Germination, Appressorium Formation, and Infection of Immature and Mature Apple Fruit by Glomerella cingulata. W. W. Shane, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650; T. B. Sutton, assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 71:454-457. Accepted for publication 9 October 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-454.

Conidial ability to germinate and produce appressoria was related to age of Glomerella cingulata culture on potato-dextrose agar. On the surface of detached apple fruit less germination and formation of appressoria occurred at 24 hr with conidia from 12-and 20-day-old cultures than from 6-day-old cultures. Conidia from 6-day-old cultures produced more infections of detached, immature, and mature Golden Delicious (GD) apples than did conidia from 12- and 20-day-old cultures. Inoculations and observations of fruit in orchard and laboratory studies with detached GD fruit showed that immature fruit were susceptible to infection by G. cingulata conidia. In the orchard, infections were observed within 35 days of petal fall and, in the laboratory, fruit were infected within 19 days of petal fall. No seasonal trend was evident in the percentage of fruit infected after 24 or 55 hr of incubation. A 20-hr incubation period at 28 C was required to establish appreciable infection of detached apple fruit.

Additional keywords: Colletotrichum gloeosporioides.