Disease Note.

Evaluation of Watermelon and Related Germ Plasm for Resistance to the Egyptian Strain of Zucchini Yellow Mosaic Virus. G. E. Boyhan, Department of Horticulture; Auburn University, Auburn, AL 36849. R. T. Gudauskas, Department of Plant Pathology; and J. D. Norton and B. R Abrahams, Department of Horticulture, Auburn University, Auburn, AL 36849. Plant Dis. 78:100. Accepted for publication 22 September 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0100D.

Of six watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) and related germ plasm lines evaluated for resistance to the Egyptian strain of zucchini yellow mosaic virus (ZYMV-E), only the cultivar Egun had a high level of resistance based on disease ratings and enzyme-linkcd immunosorbent assay (ELISA). The six entries were Egun, PI 386025, PI 386026, PI 482261-1, PI 494528, and AU-Producer. All but AU-Producer have been reported as resistant to the Florida strain of ZYMV (I). Plants were inoculated 2 wk after planting by dusting cotyledons and first true leaves, if present, with Carborundum (600 mesh), then rubbing them with sap from leaves of ZYMV-E-infected squash that were triturated in 0.05 M phosphate buffer, pH 6.8, with a mortar and pestle. Disease ratings, on a 0-5 scale (0 = no symptoms, 5 = severe symptoms), were 0.3, 1.3, 1.9, 2.5, 4.3, and 4.5 for Egun, PI 386025, PI 386026, PI 494528, AU-Producer, and PI 482261-1, respectively. Symptom ratings for PI 386025, PI 386026, and PI 494528 were statistically intermediate between those for Egun and the highly susceptible PI 482261-1 and AU-Producer. All inoculated entries had mean ELISA absorbance readings at least double those of the uninoculated checks. Egun had an ELISA absorbance reading of 0.106, statistically lower than the readings of 0.504, 0.534, and 0.263 for PI 386025, PI 386026, and PI 482261-1, respectively. Egun's reading did not differ statistically from those of PI 494528 and AU-Producer, which were 0.216 and 0.130, respectively