Biological and Molecular Screening of Some Potato Cultivars and Promising Clones for Resistance to Potato Virus X (PVX)

This study was performed to screen 35 commercial potato cultivars and 24 promising clones for resistance to Potato virus X (PVX) using biological and molecular marker assays. To purify and propagate the virus, infected potato samples were inoculated on common globe amaranth (Gompherena globose) and then on tobacco and maintained under in vitro conditions. The reaction of genotypes to PVX were evaluated based on International Potato Centre (CIP) standard method by mechanical inoculation and grafting under the greenhouse conditions. In mechanical experiment, three plants of each genotype were inoculated and the resistant genotypes were identified based on virus detection by ELISA. To determine the type of resistance, the resistant genotypes were grafted on tomato cv. Rutgers plants infected with PVX in three replications, and their infection by virus was examined using DAS-ELISA, 21 days post inoculation. The results of both experiments showed that 12 commercial potato cultivars and 11 promising clones were extremely resistance (ER) to PVX. Moreover, nine commercial potato cultivars and one promising clone showed hypersensitive resistance (HR) reaction. Twenty-six genotypes showed infection to PVX, at least in one replication, and considered as susceptible to the virus. In addition, resistance genes, Rx1 and Rx2, were successfully amplified in resistant genotypes using specific primers 5RX1 and 106RX2, respectively. However, no PCR product could be detected in the PVX susceptible and HR genotypes which were in accordance with the results of biological assays. Finally, Rx1 and Rx2 genes were detected in 13 and seven potato genotypes, respectively. It was concluded that genotypes carrying Rx1 and Rx2 genes can be used in potato breeding programs to develop new potato cultivars with desirable agronomic characteristics and resistance to PVX.