Biological and chemical characterization of active metabolites produced by Pyrenophora teres
The ethyl acetate fraction of the culture fluid of Pvrenophora teres showed a phytotoxic activity on an excised leaf of a susceptible cultivar of barley. The purification of the active metabolites involved three chromatographic methods, namely sieve size chromatography, thin layer chromatography, and high performance liquid chromatography. Three active compounds were purified. The two less active metabolites were crystallized and their structures were determined using x-ray crystallography. Both compounds are related and differ by a methoxy group on carbon #7. Pyrenoline A and Pyrenoline B are the trivial names given to these two metabolites. The third and most active compound was chemically characterized using conventional spectroscopy and was found to have the same chemical properties as Pyrenolide A, a compound that was identified by Nukina in 1980. This thesis describes the purification steps of the three compounds and their biological activities on the host plant (Hordeum vulgare sp) as well as non-host plant species. Attention was paid to Pyrenolide A. This included its production in different isolates of P. teres, its quantification, and the effect of different leaf extracts on its production. Pyrenolide A is active on a wide range of plant species including weeds. Leaf extracts from host and nonhost plants were effective in increasing toxin production in culture. Four isolates including net and spot forms, were tested for toxin production. Pyrenolide A was produced in the liquid culture of all four fungal isolates.