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Disease Note.

Black Spot, a New Field Disease of Pear in Greece. C. C. Thanassoulopoulos, Aristotelian University, Faculty of Agriculture, Plant Pathology Laboratory 540 06, Thessaloniki, Greece. E. D. Lazarides, K. and N. Efthimiades Agrochemicals Industrial and Commercial Co., Dodecanissou 24, 546 26 Thessaloniki, Greece. Plant Dis. 74:720. Accepted for publication 12 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0720E.

Extensive leaf and fruit spotting caused by Alternaria alternata (Fr.) Keissl. was observed during 1983- 1984 in central Macedonia on the pear (Pyrus communis L.) cultivars Abate Fetel, Passa Crassana, and Santa Maria. The disease reached severe levels in 1986, with tree defoliation and fruit damage resulting in losses up to 80% of the crop. Fruit and leaf inoculations with A. alternata resulted in symptoms similar to those observed in the field, and the pathogen was reisolated from infected fruit. This is the first report of this disease in the field in Greece, although the pathogen has been reported to cause a postharvest problem with pear in Greece. The fungus survived and penetrated the pericarp of fruits stored for 12 days at -20 C. Furthermore, measurements of more than 200 external spots on fruits showed that fruit spot diameter was correlated (r = 0.83 and P≤0.05) with depth of fungal penetration into the pericarp. The regression equation was y= -0.616 + 0.740X, where Y= depth of the spot and X = diameter of the spot, significant at P≤0.01. In spots up to 3 mm in diameter, the fungus did not invade the fruit pericarp.