ISOLATION, PURIFICATION, AND BIOLOGICAL-ACTIVITY OF AN INHIBITOR FROM SEPTORIA-TRITICI

Methyl-3-indole carboxylate (3-indole carboxylic acid methyl ester [ICA.Me]) was identified in liquid cultures of Septoria tritici. For physiological studies, ICA.Me was synthesized from commercial 3-indole carboxylic acid (ICA) by methylation with diazomethane. Inhibition of growth of the melanin-producing isolate ISR398 by ICA.Me on thin-layer chromatography (TLC) plates was recorded at a concentration of 0.02 mg/ml. Inhibition by 3-indole acetic acid (IAA) was recorded at a concentration of 25-fold, whereas no inhibition was recorded for ICA at a concentration range of 0.02-0.5 mg/ml. Growth of S. tritici on liquid media was differentially affected by different concentrations of ICA.Me. Complete inhibition of S. tritici isolates ISR398 and ISR8036 was recorded at 0.08 mg/ml of ICA.Me, with only partial inhibition of ISR7901 at that concentration. The regulatory effects of these indole compounds were tested on wheat coleoptile and cucumber hypocotyl segments. IAA markedly increased growth of both coleoptiles and hypocotyls at 0.5-0.7 mu-g/ml. Application of ICA and ICA.Me caused a slight decrease in hypocotyl growth and a slight increase in coleoptile growth at concentrations ranging from 0.4 to 20.0-mu-g/ml. It is possible that ICA.Me may be involved in regulating the pathogen's population on the phylloplane and within wheat tissue.