HERITABILITY OF FIELD-RESISTANCE TO POTATO LEAFROLL VIRUS IN CULTIVATED POTATO

Potato progenies in a line x tester mating design and the clonal paren ts were screened for. field resistance to potato leafroll virus (PLRV) to determine the heritability of this trait. Twelve advanced potato c lones or varieties were crossed as pistillate parents to two pollen te sters. The seedling progenies and clonal parents were exposed to aphid -transmitted potato leafroll virus for two growing seasons. Cumulative infection by potato leafroll virus was determined by post-season sero logical indexing of foliage grown from sprouted tubers after 2 years o f exposure. Narrow-sense heritability was estimated from regression of mid-parent on progeny as h(2) = 0.72. This estimate indicates a high level of useable genetic variance for PLRV resistance in advanced bree ding materials. Although variation in resistance to PLRV appears to be a quantitative trait in susceptible and moderately resistant clones, performance of the most resistant parents suggests that genes with maj or effects may be present. These results are similar to the conclusion s of other researchers who found one or two genes controlling the phen otypes of extreme resistance, resistance to infection, or suppression of virus titre.