A Complex Approach to Control Black Dot Disease in Potato

In recent years, skin blemish diseases of potato (including black dot (BD) caused by Colletotricum coccodes) have begun to be important for global potato marketing, since consumers often reject tubers with an imperfect appearance, which results in financial losses caused by the disposal of unwanted potatoes. Like for many non-fatal plant diseases, BD severity may depend on the immune status of plants influenced by other infectious agents. Using a set of 98 potato cultivars differing in their late blight (LB) resistance, we examined the correlation between the intensity of their infection with LB determined by their LB resistance and the occurrence of the BD disease under field conditions with a high background level of both diseases. Using LB-susceptible (Arizona) and moderately susceptible (Sante) cultivars, we also evaluated the effect of a crop protection against LB on BD development under the same field conditions. A strong negative correlation (r = −0.81, p < 0.05) between the LB resistance and the BD occurrence has been revealed. An experiment using the two cultivars, chemically protected against LB, showed a significant reduction in BD occurrence of 30% (cv. Arizona) and 20% (cv. Sante) compared to the untreated controls; the total yield and marketability of potatoes increased by 103.6 and 62.5% for cv. Arizona and by 65.9 and 43.8% for cv. Sante. The reduction in the LB affection of potato is one of the key factors improving the immune status of potato cultivars in relation to BD infection, so methods of LB protection should be included in a complex approach to BD control.