Environmental Factors Influencing Pseudothecial Development and Ascospore Maturation ofVenturia inaequalis

Abstract

Pseudothecial ontogeny of V. inaequalis in apple [Malus sylvestris] leaves could be separated into 2 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 lamina 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 reached maturity during exposure to 100% relative humidity. The optimum temperature range for ascogonial development was 8-12.degree. C and for ascospore maturation it was 16-18.degree. C. Cultivar and date of leaf fall had no effect on date of ascospore maturation in the spring.