Systemic induced resistance to late blight in potato by treatment with salicylic acid and Phytophthora cryptogea

Tests for systemic induced resistance (SIR) to late blight were performed with different potato cultivars in field trials and in growth chamber experiments. The non-pathogen Phytophthora cryptogea (Pc) and salicylic acid (Sa) were used as inducer agents. In the field, plants were naturally infected by Phytophthora infestans while the indoor plants were inoculated. The degree of SIR obtained varied with the cultivar used and also with the type of inducer. For example in the field the susceptible cv. St. Cecilia had enhanced resistance with Pc whereas Sa caused increased susceptibility. Inbred resistant cvs acquired increased resistance after treatment with Sa. In a separate pilot experiment in a growth chamber, Sa at two different concentrations was injected into potato seed tubers before planting. The higher Sa concentration increased resistance in genetically resistant cultivars while the lower Sa concentration brought about increased susceptibility.