Pathogens of potato (Solanum tuberosum L.) tuber (Phytophtora infestans) occurring in treatments with foliar fertilization

The paper presents the results of a three-year exact plot experiment (2008-2010) established in Ba cyny (NE Poland). Three potato cultivars were grown: medium-early ‘Adam’, medium-late ‘Pasja Pomorska’, and late ‘ l za’. The experimental factors were foliar fertilizers applied alone or in combination (Basfoliar 12-4-6, ADOB Mn, Solubor DF) and two levels of soil mineral fertilization (N1P1K1-80 kg N × ha-1, 80 kg P × ha-1, 120 K × ha-1; N2P2K2-120 kg N × ha-1, 144 kg P × ha-1, 156 K × ha-1). The experimental materials comprised potato tubers. The symptoms of soft rot (Pectobacterium carotovorum subsp. carotovorum), late blight (Phytophthora infestans) and dry rot (Fusarium spp.) were evaluated in 5 kg potato samples, and were expressed as the percentage mass of infected tubers. The rates of common scab (Streptomyces scabies) and black scurf (Rhizoctonia solani) infection were estimated on 100 tubers collected randomly after harvest, according to a nine-point scale, and were presented as a percentage infection index. In the laboratory, fungi were isolated on PDA medium from potato tubers immediately after harvest and after five-month storage. The incidence of tuber diseases depended on potato cultivars affected. The severity of tuber diseases varied between treatments with two levels of NPK fertilization and foliar fertilization. The lowest number of Fusarium-infected tubers was obtained from treatments where three foliar fertilizers were applied in combination, which was confirmed by the lowest abundance of fungal isolates. More fungi were isolated from potato tubers after harvest than after storage, but pathogens were more frequently isolated from stored tubers. After harvest, the lowest number of pathogenic fungi was isolated from the tubers of cv. ‘Adam’ in the non-fertilized treatment, and after storage – from the tubers of the late cultivars in the treatment with three foliar fertilizers applied in combination.