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Evaluation of Cotton Cultivar Susceptibility to Alternaria Leaf Spot. P. J. Cotty, Department of Plant Pathology, University of Arizona, Yuma Agricultural Center, Yuma 85364. Plant Dis. 71:1082-1084. Accepted for publication 10 July 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1082.

The relative susceptibilities of several common Arizona cotton cultivars to Alternaria macrospora were evaluated in the greenhouse. Gossypium hirsutum cv. Deltapine Acala-90 was more susceptible than G. hirsutum cvs. Deltapine 61, Acala SJ-5, and McNair 235. G. barbadense cvs. Pima S-6 and Pima S-5 were more susceptible to A. macrospora than the G. hirsutum cultivars. Cotton acreage planted to cultivars with relatively high susceptibility to A. macrospora (Pima cotton and Deltapine Acala-90) has increased rapidly in recent years in Arizona, possibly contributing to increased frequency and severity of outbreaks of Alternaria leaf spot. Results indicate that lesion diameter is a useful measure of host susceptibility.