SUSCEPTIBILITY TO POTATO LEAFROLL VIRUS IN POTATO - EFFECTS OF CULTIVAR, PLANT-AGE AT INOCULATION, AND INOCULATION PRESSURE ON TUBER INFECTION

Three potato (Solanum tuberosum) cultivars differing in susceptibility to potato leafroll virus (PLRV)-Russet Burbank (highly susceptible), Kennebec (moderately resistant), and Cascade (resistant)-showed increa sing resistance to PLRV in the field as plants aged. As inoculation ag e (measured in days after plant emergence) increased, percent tuber in fection decreased significantly (P < 0.05) in each cultivar. As inocul ation pressure (measured by viruliferous aphid-days) increased, percen t tuber infection per plant increased significantly for Russet Burbank and Cascade. The percentage of PLRV-infected tubers for any inoculati on age and aphid-day treatment combination was always less for Kennebe c and Cascade than for Russet Burbank. In each cultivar, there was no significant difference in percent PLRV infection among four size categ ories of tubers. A greenhouse bioassay classified potato cultivars int o PLRV resistance categories corresponding to previously reported fiel d resistance. However, Cascade was not as resistant in the greenhouse bioassay as it was in field trials.