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Efficiency of Ascospores of Venturia inaequalis in Producing Scab Lesions on Apple Leaves. Sandra L. Anagnostakis and Donald E. Aylor, Plant Pathology and Ecology Department, The Connecticut Agricultural Experiment Station, New Haven 06511. Plant Dis. 75:918-920. Accepted for publication 11 March 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0918.

McIntosh apple trees at three early stages of leaf expansion were exposed to freshly discharged ascospores of Venturia inaequalis in a dew chamber at 1819 C. Spores deposited on glass coverslips positioned next to the leaves at each node were counted. Spores on some coverslips were also tested for viability. Lesions were noted after the trees had been kept in a growth chamber (12 hr of light at 25 C followed by 12 hr of darkness at 20 C) for 1127 days. The efficiency of lesion production was calculated as the ratio of the number of lesions per unit of leaf surface area at the time of inoculation to the number of spores per unit of coverslip area. Lesion-forming efficiency averaged 5, 6, and 14% for the three groups of trees.