Assessing the resistance of potatoes to powdery scab (Spongospora subterranea (Wallr.) Lagerh.)

The reaction of nine cultivars to infection by Spongospora subterranea (powdery scab) was studied in two successive years of trials in naturally infested field soil and in artificially-inoculated field soil contained in brick-sided beds. The incidence of infection was recorded on a 1-9 scale, with complete absence of the disease scoring 9. The correlation coefficient (r) between scores from bed and field was 0.84 (1985) and 0.81 (1986). The field test gave satisfactory discrimination between resistant and susceptible cultivars in only one year, but the bed test gave good results in both years and is suggested as a small-scale alternative to field trials for this disease.