The use of four different assessment methods to establish relative potato tuber blight resistance for breeding

Four methods of assessment of tuber blight resistance were compared. On the day of harvest in August undamaged tubers were inoculated and incubated in the laboratory in controlled conditions (method a) or incubated first for seven days in a clamp (b) or tubers from storage were tested in January after damage (c) or in November by tuber slice test (d). Over three years, 41 varieties were examined and on average, differences of 2.2 to 3.2 score on a 1-9 scale, showed significant differences between cultivars. The interactions varieties x years, varieties x methods and years x methods were significant in an analysis of variance over methods a, c, d together. Method-specific differences are explained as tissue-specific resistance of some cultivars. Tissue-specifity of components of resistance require to use a whole tuber test (method a) in case of low tuber injuries during harvest in practice. The resistance of the methods correlated with each other r=0.2-0.5. The state of skin, number and size of lenticels did not correlate with the resistance. Tuber blight resistance in the German descriptive list of cultivars was over-rated by about 2 scores.