Assaying for Pollen Drift from Transgenic 'Rainbow' to Nontransgenic 'Kapoho' Papaya under Commercial and Experimental Field Conditions in Hawaii

In 1992, papaya ringspot virus (PRSV) was discovered in the Puna district of Hawaii island where 95% of the state of Hawaii's papaya was being grown. By 1998 production in Puna had decreased 50% from 1992 levels. A PRSV-resistant transgenic papaya 'Rainbow' containing the coat protein gene of PRSV was released commercially in Hawaii in 1998, and saved the papaya industry from further devastation. In the ensuing years since the release of the transgenic papaya, a number of farmers grew hermaphrodite nontransgenic 'Kapoho' papaya in close proximity to plantings of hermaphrodite transgenic 'Rainbow' papaya. These plantings provided a unique opportunity to assay for transgenic-pollen drift under commercial conditions. Between 2004 and 2010, assays for the GUS (beta-glucuronidase) transgene in embryos were done to study transgenic-pollen drift in commercial 'Kapoho' plantings and in replicated field plots. Very low pollen drift (0.8%) was detected in fruit of 'Kapoho' trees in the border row of one plantation when 90 embryos were assayed per fruit, while no pollen drift was detected in four other commercial plantings in which eight embryos were tested per fruit. Pollen drift averaged 1.3% of tested embryos in field plots where individual hermaphrodite 'Kapoho' trees were adjacent to two or four 'Rainbow' trees. In contrast, 67.4% of tested embryos were GUS positive in similarly located female 'Kapoho' trees. The very low transgene flow to closeby 'Kapoho' plantings is likely due to the fact that hermaphrodite trees are used commercially in Hawaii and that these trees are largely self-pollinated before the stigma is exposed to external pollen.