The field resistance of potato cultivars to foliar late blight and its relationship with foliage maturity type and skin type in Brazil

The use of resistant cultivars is the preferred control method for plant diseases. This approach is attractive owing to its high efficacy, low cost, and ease of implementation. This work aimed to assess the resistance of potato cultivars to foliar late blight (Phytophthora infestans) under different environmental conditions. It further aimed to assess the relationships between resistance to foliar late blight and foliage maturity type and between resistance to foliar late blight and the skin type of the potato. Three experiments were performed in two different regions of the state of Minas Gerais with different environmental conditions. The first and second experiments used 34 cultivars (treatments). The third experiment used 17 cultivars. The severity of foliar late blight in each plot was quantified every 2 days using a descriptive scale. The values of the epidemiological variables were then calculated. The proposed levels of resistance to foliar late blight were defined as: resistant (R), moderately resistant (MR), moderately susceptible (MS) and susceptible (S). The majority of potato cultivars were susceptible to foliar late blight. The resistance levels of some cultivars to foliar late blight used in these experiments changed according to the pathogen population and environmental conditions. The cultivars with the highest levels of resistance to foliar late blight (resistant and moderately resistant) were later maturity. Most cultivars that have been classified as moderately susceptible or susceptible were earlier maturity. In general, cultivars that are more resistant to foliar late blight had a rougher skin, whereas the skins of the more susceptible cultivars had smoother.