Why genetically engineer PRSV resistance into papaya?
Traditional strategies like those mentioned above have had limited success. First, the virus is very efficiently spread from plant to plant by about 60 species of aphids and transmission is “non- persistent,” meaning the aphids need to feed on a PRSV-infected plant for only a few seconds to pick up the virus. This makes it virtually impossible to control the virus by insect control or by discarding diseased plants. Second, there is no known natural resistance to the disease, although tolerant varieties manifesting reduced symptoms have been identified. In the Philippines, a tolerant hybrid cultivar, Sinta, has been a commercial success. Unfortunately, breakdown of resistance and loss of its effectiveness have been reported as early as two years after the release of the hybrid. Third, production under netting is an option but this requires large initial capital investments, which most small-scale producers can barely afford. Fourth, cross-protection has been used in Hawaii, Thailand, and Taiwan, with limited success. Protection is virus strain specific and never complete. Cross-protection, as well as quarantine and even eradication are only temporary solutions. Finally, considerable variation exists in the genomic sequences of various strains of PRSV. Because of these limitations, scientists have turned to genetic engineering and the use of the PRSV “coat protein resistance” strategy to develop transgenic PRSV-resistant papaya.