The term papaya ringspot (PRS) was first coined by Jensen in 1949 to describe a papaya disease in Hawaii. Previously described diseases such as papaya mosaic (caused by Papaya mosaic virus) and watermelon mosaic (caused by Watermelon mosaic virus-1) were shown recently to be caused by Papaya ringspot virus (PRSV). The virus (PRSV) causes a major disease of papaya and cucurbits and is found in all areas of the world where papaya and cucurbits are cultivated. The primary host range of PRSV is limited to papaya (Caricaceae) and cucurbits (Cucurbitaceae), with Chenopium amaranticolor and C. quinoa (Chenopodiaceae) serving as local lesion hosts. The virus is grouped into the papaya infecting type (PRSV-P) which affects both papaya and cucurbits, and the cucurbit infecting type (PRSV-W) which affects cucurbits but not papaya. PRSV belongs to the genus Potyvirus, a large and economically important group of plant infecting viruses in the family Potyviridae. Virions of PRSV are filamentous and flexuous measuring 760-800 x 12 nm with a monopartite single-stranded positive sense RNA as its genome. Like other potyviruses, PRSV is transmitted in a nonpersistent manner by several species of aphids. Genetically engineered (GE) papaya has been used to successfully control the disease caused by PRSV in Hawaii.