“…Resistance to infection (I R) is overcome if the inoculum dose is sufficient, and this is polygenically controlled (Ross, 1958;Davidson, 1973Davidson, , 1980, whereas resistance to accumulation (AR), which decreases but does not prevent virus multiplication, may be determined by a single gene (Barker & Solomon, 1990). A third component of virus-specific resistance is recognized, decreased PLRV movement from infected foliage to tubers (McKay & Clinch, 1951;Hutton & Brock, 1953). This is independent of the non-specific 'mature plant resistance' which increases as potato plants age (Beemster, 1987).…”