Co-Authors:
Fewell, A.M., Department of Biological Sciences, University of Exeter, Exeter, United Kingdom
Roddick, J.G., Department of Biological Sciences, University of Exeter, Exeter, United Kingdom
Weissenberg, M., Department of Biological Sciences, University of Exeter, Exeter, United Kingdom, Department of Chemistry of Natural Products, A.R.O., The Volcani Center, P.O.B. 6, Bet Dagan, Israel
Abstract:
Inhibition of mycelium development in Phoma medicaginis and Rhizoctonia solani by solamargine and solasonine generally increased with increasing pH. P. medicaginis was the more susceptible species and solamargine the more potent compound. Solasonine was inactive against R. solani over the tested pH range (5-8). Dose-response curves confirmed these differential effects. Solamargine caused 50% growth inhibition in P. medicaginis at 60 μM (at pH 7) whereas no other treatment achieved this effect at 100 μM. Combinations of 50 μM of each glycoalkaloid produced synergistic effects against both fungi, especially R. solani which was essentially unaffected by either compound, but significantly inhibited by a 1 : 1 mixture of the two. The magnitude of the synergism was not affected by a pH change between 6 and 7. Spore germination in Alternaria brassicicola was markedly inhibited by 100 μM solamargine but unaffected by 100 μM solasonine or either compound at 50 μM. In P. medicaginis, neither glycoalkaloid was inhibitory up to 150 μM. In combination, the two compounds caused synergistic effects in both species, but to a much greater extent in A. brassicicola. © 1994.