Mycosphaerella melonis on Greenhouse Cucumber. M. W. Olsen, Research Assistant, Department of Plant Pathology, University of Arizona, Tucson 85721. M. E. Stanghellini, Professor, Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Dis. 65:157-159. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-157.

Mycosphaerella melonis, causal agent of gummy stem blight on cucurbits, infected seedlings, mature plants, and fruit of Cucumis sativus ‘Toska’ in experimental and commercial greenhouses in Tucson, Arizona. The pycnidial stage of the fungus, Phyllosticta sp., caused a severe seedling disease. Because attempts to isolate the fungus from seed were unsuccessful, a Phyllosticta sp., originating from naturally infected Opuntia sp., was implicated as a possible source of indigenous inoculum. Morphological characteristics of pycnidia and pycnidiospores from infected Opuntia and infected cucumber were identical. Reciprocal inoculations between isolates from Opuntia and cucumber were successful.