Evaluation of potato virus X resistance in potato cultivars and identification of an innate immunity-independent resistance phenotype

Abstract

Potato virus X (PVX) is a widely distributed viral pathogen that causes significant losses in potato production by co-infecting with potato virus Y or potato virus A. In this study, the resistance of 23 potato cultivars to PVX was dissected in detail using a PVX infectious clone containing a yellow fluorescent protein (YFP). Among them, four potato cultivars (Longshu-3, Eugene, Atlantic and Waiyin-2) were found to carry an Rx gene that confers extreme resistance to PVX; one cultivar (Waiyin-1) displayed partial resistance and was able to delay PVX infection by ~ 5 days; while the rest eighteen potato cultivars were susceptible to PVX. Moreover, we found that the replication but not cell-to-cell or long-distance movement of PVX was inhibited in Waiyin-1. Finally, we determined that the expression of pathogenesis-related (PR) genes in Waiyin-1 was not triggered by PVX infection at early infection stage, whereas they were triggered in the Rx-carrying cultivar Atlantic during this period of time. In conclusion, our results confirm that Rx is a major type of resistance gene in potato cultivars in the Northeast part of China. Furthermore, the possible mechanism underlying Waiyin-1 resistance to PVX is discussed.