In 1963, melon (Cucumis melo L.) plant introductions (PI) 124112 and PI 180280 were reported variable in response to inoculation with the T-1 or Freitag's isolates of watermelon mosaic virus. Most plants were symptomless, but some had small pinpoint necrotic lesions on cotyledons and leaves. The T-1 and Freitag's isolates of watermelon mosaic were later designated watermelon mosaic virus 1, and more recently renamed papaya ringspot virus watermelon strain (PRSV-W). When inoculated with California or Florida isolates of PRSV-W in 1993, WMR 29 a western U.S. shipping type melon derived from PI 180280 was symptomless (incompatible reaction) and SDS-immunodiffusion assays were negative. In contrast when inoculated with the same PRSV-W isolates, PI 124112 had incompatible reactions characterized by wilting, local lesions, systemic necrotic spots and necrosis and negative SDS-immunodiffusion assays.