Estimation of disease scale (1-9) values from RAUDPC

The area under the disease progression curve (AUDPC) was calculated from the date of first occurrence of late blight until the last observation of the disease in the trial according to Shaner and Finney (1977).

Where t = is the time in days of each reading, y = is the percentage of affected foliage at each assessment and n = is the number of assessments. AUDPC was standardized to RAUDPC (relative area under disease progression curve) values according to Fry (1978).

Estimation of 1-9 scale values from RAUDPC values were calculated according to Hansen et al. (2005); for this the linear regression model: y = a + bx, where y = observed values; a = intercept; b = slope and x = (√RAUDPC for variety/√RAUDPC for cultivar Toluca) × 100. A smaller value of the index indicates higher resistance in a potato cultivar. Estimated scale values for cultivars tested in both years were compared with scale values for the same cultivars from the European Cultivated Potato Database, breeding company Agrico website and breeder information from Estonian Crop Research Institute, where the scale for resistance against foliar blight is defined as: 1 (very low); 2 (very low to low); 3 (low); 4 (low to medium); 5 (medium); 6 (medium to high); 7 (high); 8 (high to very high); 9 (very high).