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Effect of Potato Alkaloids on the Growth of Alternaria solani and their Possible Role as Resistance Factors in Potatoes. S. L. Sinden, Plant Physiologist, Plant Genetics and Germplasm Institute, Agricultural Research Center, ARS, USDA, Beltsville, Maryland 20705; R. W. Goth(2), and Muriel J. O’Brien(3). (2)(3)Plant Pathologists, respectively, Plant Genetics and Germplasm Institute, Agricultural Research Center, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 63:303-307. Accepted for publication 7 September 1972. DOI: 10.1094/Phyto-63-303.

Solanine, chaconine, and solanidine inhibited the radial growth of Alternaria solani on potato-dextrose agar. Solanidine was the most inhibitory of the three alkaloids, followed by chaconine and solanine, respectively. At a concentration of 250 ppm, solanine caused a 33% inhibition of growth after a 96-hr incubation period at 24 C. Chaconine was twice as inhibitory, producing a 56% inhibition of growth at a concentration of 250 ppm. Young (30-day-old) potato leaves contained 1,570 ppm of the glycoalkaloids, whereas senescent (120-day-old) leaves contained only 260 ppm. An increased susceptibility of leaves to A. solani was correlated with a decrease in glycoalkaloid concentrations in leaves as the potato plants aged. The results suggest a possible role for alkaloids in restricting lesion development in young leaves of the potato plant infected with A. solani.