SUSCEPTIBILITY OF POTATO CULTIVARS TO THE N AND O STRAIN OF POTATO-VIRUS-Y (PVY) AND OTHER POTYVIRUSES

Under insect-proof greenhouse conditions, potato plants of several cul tivars with different susceptibilities to PVY were mechanically inocul ated with PVY isolates of the N and O strain. While extremely resistan t cultivars, which carry Ry(sto) genes from the wild potato Solanum st oloniferum, were not infected with any of these strains, PVY susceptib ility varied with the inoculated strain especially for cultivars with moderate resistance. Differences in the strain-specific resistance had no influence on the ranking of potato cultivars with regard to their overall PVY susceptibility. The extremely resistant cultivars could al so nor be infected with other potyviruses such as potato virus A (PVA) , potato virus V (PVV) and tobacco etch virus (TEV). Therefore, it is suggested that the products of the Ry genes were elicitated by common potyvirus product(s) or targeted to common feature(s) of this virus ge nus. The broad resistance may be useful in regions where potatoes and tobacco are grown in the same area, to prevent mutual infections with potyviruses.