Resistance to Potato Leafroll Virus in Potato Plants Transformed with the Coat Protein Gene or with Vector Control Constructs

The results of greenhouse evaluations of potato leafroll virus (PLRV) resistance in transgenic potato plants are reported. Russet Burbank and Ranger Russet plants were transformed via Agrabacterium-mediated gene transfer with three constructs, one carrying the native viral coat protein (CP) gene, another containing a modified form of the CP gene designed to optimize protein expression, and a third consisting of the binary vector plasmid only. A statistically significant correlation (P < 0.01) was found between incidence of infection within replications of a given clone and virus titers of the infected plants. Resistance to PLRV titer buildup as measured by enzyme-linked immunosorbent assay was observed among clones in all three construct populations. Plants transformed with the modified CP gene did not exhibit greater levels of resistance to PLRV than plants transformed with the native CP gene. Of particular interest are several highly resistant lines that were derived by transforming Ranger Russet with the control construct carrying only vector sequences and the neomycin phosphotransferase (NPTII) gene. This resistance, which is heritable and has been verified in three separate inoculations, indicates that a component of PLRV resistance in transgenic potato is associated with vector DNA or the tissue culture process. Possible explanations for this novel type of resistance and its implications are discussed