Resistance to Papaya Ringspot Virus: a Review

Papaya is known to be affected by many viruses, out of which the most important are PRSV; PRSV-P (Papaya exhibits yellowing, leaf distortion, and severe mosaic) and PRSV-W (PRSV-W causes mottling and distortion of leaves and fruit). The type that gave the virus its name is the Type P isolates (PRSV-P). The other type, Type W isolates (PRSV-W), does not infect papaya. Isolates of PRSV-W do infect cucurbits such as watermelon, cucumber, squash, etc., and were originally known as Watermelon Mosaic Virus. It has been documented as PRSV is transmitted by several species of aphids like Aphis nerii, Aphis gossypi, Aphis spiraecola, Myzus persiciae, Toxoptera aurantii, Aphis craccivora and Rhopalosipum maidis in a nonpersistant manner. Prevention through Quarantine and Geographical displacement is an important aspect of their management. IPM for various aphid species has been successfully achieved by using Bio-control agents like using fungi Lecanicillium lecanii, Beauveria bassiana or Isaria fumosorosea. Given pathogen derived resistance, the coat protein (CP) gene from a mutant mild strain of PRSV provided a high level of resistance to Hawaiian strain of PRSV has been reported. Transgenic papaya to prevent PRSV has been developed soon after the successful development of transgenic tobacco expressing CP genes of the Tobacco Mosaic Virus (TMV) showing resistance. However, the success and effectiveness of CP mediated PRSV resistance depend on the origin of PRSV isolates and their translatable and untranslatable constructs. The discovery of RNA interference (RNAi) mediated resistance in transgenic tobacco against potato virus Y has emergd as an important molecular tool for crop improvement and the study the function of gene and gene silencing mechanism using RNAi mediated resistance may be one of the important tools for managing the virus in case of papaya ringspot virus. Advances in our knowledge and adoption of various technologies like pathogen-derived resistance, replicase gene mediated resistance, cross-protection, post-transcriptional gene silencing method with a better understanding of the occurrence, symptoms of disease, transmission, vector of the virus and their genome structure will provide various researchers to study and develop proper strategies for the better management of the disease.