yields (Gonsalves 1998). The effects of this virus are so severe that year-round cultivation might not be profitable and infected plantations are often abandoned. Efforts to control the aphids, or to conventionally breed for protection from the virus have been unsuccessful. Tolerance of the virus can sometimes be achieved by deliberately infecting the plants with a mild strain of PRSV, but this is laborious, unpopular with farmers, and only partially effective (Gonsalves 1998).

Papaya was introduced to the Hawaiian island of Oahu in the 1940s and PRSV began infecting the plantations in 1945. The industry then moved to the island of Hawaii, as did the virus; the small, isolated region of Puna remained virus-free until 1992. Meanwhile, Dennis Gonsalves and his colleagues at Cornell University began developing transgenic papaya with protection from PRSV in the hope of rescuing Hawaii's tenuous papaya industry. First they fused a coat protein gene from a mild strain of PRSV to a kanamycin-resistance marker. The linked transgenes were then inserted into the genomes of two local cultivars, christened UH Rainbow and SunUp. The cultivars were highly protected from the Hawaiian strains of the virus and were deregulated in 1996; this allowed the industry to begin recovering from its complete collapse. The virus is unlikely to disappear, however, because it also infects cucurbits and other hosts that occur nearby. Farmers expect transgenic protection to be a boon to the local economy, but the boon could be temporary if the pathogen evolves a way to circumvent the plants' protective mechanism. Another concern is the possibility that other races of PRSV will reach Hawaii. The transgenic papaya is not protected from isolates of the PRSV from outside Hawaii, but further research by the Gonsalves group suggests that protection from a broader spectrum of PRSV races can be obtained (Gonsalves 1998). Parallel research projects are now under way in other papaya-growing countries.

The human health risks that were evaluated before deregulation of transgenic papaya are similar to those described above for squash. As with Asgrow's squash, the papaya's viral coat protein is not expected to jeopardize human health, because consumers already ingest this compound in nontransgenic food. Gene flow to feral or wild relatives was not an issue because no wild relatives occur in Hawaii, Puerto Rico, or Florida, and the crop itself is not weedy.


The above case studies described the type of data and information used for regulatory review of transgenic pest-protected plants. This sec-

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