Recently, we received a very interesting watermelon sample that was infected with Papaya Ringspot Virus (PRSV). This is only the second time we have seen this disease in the clinic. PRSV causes diseases on cucurbits and papaya plants worldwide. The most obvious symptom of PRSV infection is the formation of sunken ring spots on the fruit. These spots are very diagnostic of the disease. Other symptoms include mosaic or mottling of the leaves and oily streaks on the stems and petioles. In some cases, the leaves may be severely narrowed, which gives them a “shoestring” like appearance.
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| Rinspot symptoms of PRSV (Photo by: Jennifer Pries) |
The two major strains of PRSV are PRSV-W and PRSV-P. PRSV-W (the watermelon-infecting type) used to be known as Watermelon Mosaic Virus I, and can only infect cucurbits. PRSV-W is the major strain found in the Southeastern US, but it is also present in tropical areas where PRSV-P is present. PRSV-P (the papaya-infecting type) is only found in tropical and subtropical areas were papayas are grown, but PRSV-P can also infect cucurbits. Controlling this disease is somewhat difficult, especially in papaya. Genetic resistance to PRSV is available in some commercial varieties of cucurbits and is the most effective way of controlling the disease. Unfortunately, resistance has not been found in watermelon. Aphid control is not practical because of the nonpersistant manner in which the virus is transmitted.
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