VIEW ARTICLE

Ecology and Epidemiology

Environmental Factors Influencing Pseudothecial Development and Ascospore Maturation of Venturia inaequalis. J. R. James, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650, Present address of senior author: CIBA-GEIGY Corp., P.O. Box 18300, Greensboro, NC 27419; T. B. Sutton, assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 72:1073-1080. Accepted for publication 15 October 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1073.

Pseudothecial ontogeny of Venturia inaequalis in apple leaves could be separated into two distinct phases. Ascogonia developed after leaf fall until the lumina of the pseudothecia were filled with pseudoparaphyses. Development of asci and ascospores was initiated in the spring only after a dormant or rest period during which no observable development was detected in the lumina of the pseudothecia regardless of temperature or moisture treatments. Laboratory and field studies made during a 3-yr period indicated that moisture was a limiting factor. Pseudothecia did not develop in air-dried apple leaves, but they did reach maturity during exposure to 100% relative humidity. The optimum temperature range for ascogonial development was 8–12 C and for ascospore maturation it was 16–18 C. Cultivar and date of leaf fall had no effect on date of ascospore maturation in the spring.