The Influence of Temperature and Moisture on the Quantitative Production of Pseudothecia ofVenturia inaequalis

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Abstract
The influence of temperature and moisture on the quantitative production of pseudothecia by Venturia inaequalis in sterilized, inoculated leaf disks and in naturally-infected leaf disks [McIntosh apple] was studied under laboratory conditions. The disks were exposed in a factorial experiment to seven temperatures (0, 4, 8, 12, 16, 20 and 24.degree. C), four moisture levels (wet, 95% RH, 88% RH and dry), and two treatment durations (3 and 7 days) at five stages of pseudothecial development (stage 2, pseudothecial initial; stage 3, ascogonium formation; stage 5, dormant period; stage 7, asci one-half mature size; and stage 9, spore formation). More pseudothecia were produced in leaf disks in the wet and 95% RH treatments than in the 88% RH and dry treatments. The optimum temperatures for pseudothecial development at stages 2, 3, 5, 7 and 9 were 4, 8, 8, 16 and 20.degree. C, respectively. The mean number of pseudothecia produced in naturally-infected leaf disks over all treatments was lower than the mean number of pseudothecia produced in the inoculated leaf disks; however, the general response to the treatments was similar in the two types of disks. Number of pseudothecia produced in the inoculated leaf disks was significantly correlated with inoculum concentration and length of initial incubation at 20.degree. C.