Interactive antifungal activity of the glycoalkaloids α-solanine and α-chaconine

Abstract

The antifungal activity of the major potato glycoalkaloids, α-solanine and α-chaconine, against Ascobolus crenulatus, Alternaria brassicicola, Phoma medicaginis and Rhizoctonia solani has been examined. Both compounds showed reduced activity at lower pH (6 cf 7) and, in all cases, chaconine was the more inhibitory of the two compounds. A 1 : 1 mixture of solanine and chaconine produced marked synergistic effects, the magnitude of which varied with the fungus, concentration and pH. While individual glycoalkaloid activity declined substantially with decreasing pH and concentration, in most cases the inhibitory effect of the glycoalkaloid combination showed only a small reduction. In some cases, major inhibition was achieved with mixtures, the levels of individual glycoalkaloids in which showed no antifungal activity at all. The synergism between solanine and chaconine extended over a wide range of glycoalkaloid ratios with as little as 10–20% of either compound in the mixture causing a pronounced enhancement of the effect of any single glycoalkaloid, especially chaconine. The generally reduced sensitivity of R. solani to solanine and chaconine, both individually and in combination, is in keeping with this fungus being a serious pathogen of potato.