Abstract
Translatable and non-translatable versions of the coat protein gene (CP) of a Papaya ringspot virus (PRSV) isolate from Jamaica were used to transform papaya (Carica papaya L.) embryos by microprojectile bombardment. One hundred and fifty transgenic calli were obtained, of which 39 were regenerated and established in the greenhouse. Coat protein was detected (75%) by polymerase chain reaction; varying levels of CP ribonucleic acid (RNA) transcript and expression protein were detected by Northern analysis and enzyme-linked immunosorbent assays, respectively. R0 and R1 plants were challenged under greenhouse conditions with the homologous PRSV isolate from which the transgene was derived and heterologous isolates from other locations across Jamaica. R0 plants carrying the translatable CP were highly resistant and more resistant (78%) to inoculation with the homologous PRSV than lines transformed with the non-translatable CP (10%). However, 15% of the latter lines exhibited a recovery phenotype whereby plants appeared to out-grow systemic infection. In the following generation, R1 plants, carrying either version of the CP, exhibited strong resistance but lower levels of resistance (6-46%) to heterologous PRSV isolates. The results suggest that high, broad-spectrum resistance against PRSV isolates across Jamaica should be attainable in subsequent generations by conventional breeding within and between selected transgenic lines carrying translatable and nontranslatable versions of the virus CP gene.
