Line 63-1: A New Virus-resistant Transgenic Papaya

Abstract

The disease resistance of a transgenic line expressing the coat protein (CP) gene of the mild strain of the papaya ringspot virus (PRSV) from Hawaii was further analyzed against PRSV isolates from Hawaii and other geographical regions. Line 63-1 originated from the same transformation experiment that resulted in line 55-1 from which the transgenic commercial cultivars, `Rainbow' and `SunUp', were derived. Plants of line 63-1 used in this study consisted of a population from a self pollinated R0 bisexual plant. ELISA and PCR tests provided evidence that there are at least two segregating CP loci. To allow for comparison with reactions of the previously reported line 55-1, virus isolates from Hawaii, Brazil, Thailand, and Jamaica were used to challenge seedlings of 63-1. Unlike line 55-1, a significant percentage of inoculated transgenic plants were susceptible to isolates from Hawaii. However, a proportion of plants were resistant to the non-Hawaiian isolates. In contrast, previous work showed that all plants of the hemizygous line 55-1 were susceptible to PRSV isolates from Brazil, Thailand, and Jamaica. Line 63-1, therefore, presents Hawaii with PRSV-resistant transgenic germplasm that could be used as a source of transgenes for resistance to PRSV isolates within and outside of Hawaii.