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Expression of Partial Resistance to Cherry Leaf Spot in Cultivars of Sweet, Sour, Duke, and European Ground Cherry. T. M. Sjulin, Department of Horticulture, Michigan State University, East Lansing 48824. A. L. Jones, and R. L. Andersen. Department of Botany and Plant Pathology and The Pesticide Research Center, and Department of Horticulture, Michigan State University, East Lansing 48824. Plant Dis. 73:56-61. Accepted for publication 10 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0056.

Characteristics of infection and defoliation of cultivars of sweet, sour, duke, and European ground cherry by Coccomyces hiemalis were studied in the field and greenhouse to determine their suitability for evaluating cultivars of cherry for resistance to cherry leaf spot. Under field conditions, no cultivar was highly resistant to infection by leaf spot, but the progress of defoliation for sweet and European ground cherry was slower than that for duke and sour cherry. Among 25 cultivars tested in the field, Yellow Glass, Schmidt, and Emperor Francis sweet cherry displayed the least, and Montmorency sour cherry and Krassa Severa duke cherry the greatest, defoliation severity. In the greenhouse, inoculated leaves of sweet cherry required more days before 50% of the lesions were visible, had smaller lesions, and produced fewer conidia per lesion than inoculated leaves of sour cherry. High correlations existed between the severity of defoliation in the field and the infection characteristics of number of days for 50% of the lesions to become visible, rate of lesion appearance, lesion size, spores per lesion, and reproduction efficiency in the greenhouse. Accordingly, greenhouse studies could be useful in identifying cherry seedlings with partial resistance or tolerance to leaf spot. There was little difference in the defoliation of SHT-2 and SHT-3, two progeny with apparent resistance to leaf spot in a seedling nursery, from that of Montmorency sour cherry in the field, but lesions on SHT-2 and SHT-3 produced fewer spores than those on Montmorency in the greenhouse.

Keyword(s): Prunus avium, P. cerasus, P. fruticosa, P. gondouinii.