AN APPROACH TO FIELD SCREENING POTATO GENOTYPES FOR POTATO LEAF ROLL VIRUS-RESISTANCE

Eight potato cultivars and two advanced breeder selections were assess ed for field resistance to the potato leaf roll virus (PLRV) following field exposures in which PLRV-infected Russet Burbank plants were use d as inoculum sources within treatments. This screening protocol provi ded consistent PLRV resistance ratings despite year-to-year variation in PLRV pressure. Secondary disease incidence based on enzyme-linked i mmunosorbent assay (ELISA) of foliage from tuber progeny ranged from 0 -87% in 1990 and 0-67% in 1991, and was consistent with reported PLRV resistance ratings for eight of ten genotypes. Agreement between visua l assessment and ELISA on plants from harvested tubers was 94% in 1990 and 83% in 1991, for all genotypes. However, agreement data were inco nsistent from year-to-year, with the exception of three genotypes. In both years, current season infection, based on ELISA of foliage, was d etected in less than two percent of the plants and, was inadequate as a measure of secondary PLRV incidence. Green peach aphid (GPA) populat ions did not differ among genotypes at sampling times during the seaso n, but the PLRV concentration in GPA colonizing Russet Burbank plots w as significantly higher than in GPA colonizing any other genotype.