TRANSLOCATION AND MECHANICAL SPREAD OF A MINNESOTA ISOLATE OF POTATO-VIRUS-S IN POTATOES

Potato cultivars Norland, Kennebec, and Russet Burbank were inoculated with a Minnesota isolate of potato virus S (PVS) in the field. The in cidence of secondary infection, measured by enzyme-linked immunosorben t assay (ELISA), indicated that significantly more PVS infection occur red in Russet Burbank than Norland or Kennebec, and that Norland had s ignificantly more infection than Kennebec (P less than or equal to 0.0 1). Mature plant resistance was not observed. Rapid reinfection of PVS -free seedlots resulted from inoculum point-sources when routine culti vation practices were followed. Reinfection rates were significantly g reater for seedlots grown at Grand Forks, ND, when compared with seedl ots grown at Becker, MN, during both years of the study (P less than o r equal to 0.01). After two years in the field, reinfection rates for Norland (71.8%) and Russet Burbank (73.0%) did not differ significantl y, but were significantly greater than the reinfection rate for Kenneb ec (29.5%) (P less than or equal to 0.01). In greenhouse-grown plants, PVS moved out of rub-inoculated leaves within 24 hr, however, 13 and 20 days were required before PVS was detected with ELISA in foliage ab ove and below the inoculated leaf, respectively. The frequency of PVS detection was significantly greater in foliage above the inoculated le af compared to foliage below the inoculated leaf (P less than or equal to 0.05). Translocation of PVS from inoculated leaves to daughter tub ers occurred within 13 days for Russet Burbank and Norland and within 20 days for Kennebec.