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Effect of Environment and Host on Sporulation of Alternaria macrospora in Cotton. J. Rotem, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; W. Blickle(2), and J. Kranz(3). (2)(3)Tropeninstitut, University of Giessen 6300, West Germany. Phytopathology 79:263-266. Accepted for publication 5 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-263.

Prolific sporulation of Alternaria macrospora in cotton was induced by light (under either wet or dry conditions) between two wet periods in darkness. The wet-and-dark period after induction by light affected sporulation more than the wet-and-dark period before induction. More spores per unit area were produced on cotyledons than on leaves. On both organs, the number of spores increased and the lesioned tissue changed from greenish to chlorotic and to necrotic. These changes also were associated with lower minimum and higher maximum temperatures and extension of the optimum from 30 C in greenish leaves to a range of 25 to 30 C in chlorotic leaves, and 20 to 30 C in necrotic leaves. The earliest peak of sporulation, the longest infectious period, and the highest total production of spores occurred under relatively warm, cool, and medium temperature regimes, respectively. As a result of the induction by light, many more spores were produced under several relatively short dew periods at night interrupted by dry days than under one long and uninterrupted dew period in darkness. Proneness to sporulate increased with the increase in leaf age from 2 to 5 wk.

Additional keywords: epidemiology, humidity