SEVERITY OF LATE BLIGHT (PHYTOPHTHORA INFESTANS /MONT./ DE BARY) AND EARLY BLIGHT OF POTATO (ALTERNARIA SOLANI SORAUER, A. ALTERNATA /FR./ KEISSLER) IN THREE POTATO CULTIVARS UNDER DIFFERENTIATED SOIL AND FOLIAR FERTILIZATION

Late blight (Phytophthora infestans /Mont./ de Bary) and early blight of potato (Alternaria solani Sorauer, A. alternata /Fr./ Keissler) belong to very severe potato diseases, which are able to decimate potato plantations in Poland and worldwide. In a strict plot experiment, run from 2008 to 2010, the severity of late blight (Phytophthora infestans) and early blight (Alternaria spp.) was determined, during the growing season, on three potato cultivars: medium-early cv. Adam, medium-late cv. Pasja Pomorska and late cv. Sleza, which received NPK soil fertilization (two fertilization levels) and foliar nutrition consisting of complex fertilizers with micronutrients (Basfoliar 12-4-6, ADOB Mn, Solubor DF). The extent to which the pathogens infected potato plants was evaluated twice during each growing season, on a 9-degree scale (PIETKIEWICZ 1985), and the results (means from two observations) expressed as a percentage represented an infestation index. During the first two seasons, the late blight symptoms were significantly less severe on the late and medium-late rather than on the medium-early cultivar. In the last year, the cultivars Adam and Sleza proved to be the least infected by P. infestans. Differences in the intensity of early blight of potato on the examined potato cultivars appeared in the third year, when cv. Adam proved to be the healthiest variety. Some non-significant differences were demonstrated in the severity of the diseases depending on the applied foliar fertilization and the levels of NPK fertilization.