Variation in metabolite production by Septoria nodorum isolates adapted to wheat or to barley

The production of secondary metabolites by S. nodorum strains was examined in relation to their adaptation to wheat or to barley. Eleven strains of each type previously characterized were tested for the production in culture of (-)-(3R)-mellein (ochracin), (3R)-O-methylmellein; ( -)-(3R, 4R)-4-hydroxymellein, ( -)-(3R, 4S)-4-hydroxymellein, mycophenolic acid, septorine, N-methoxyseptorine, N-methoxyseptorinol, and a new compound (= UN). Mellein was produced by every strain. Both 4-hydroxymellein isomers were yielded by all wheat-adapted strains and six barley-adapted strains. Most of the strains produced mycophenolic acid. On the other hand the pigmentation of culture filtrates of wheat-adapted strains was pale-yellow whereas the pigmentation of barley-adapted strains was grey-blue. The productions of O-methylmellein, septorine, N-methoxyseptorine and N-methoxyseptorinol were typical for wheat-adapted strains. The detection of UN was restricted to the filtrates of barley-adapted strains. If the pigmentation of filtrates and the production of septorines, UN and O-methylmellein are considered the strains fell into two groups. This classification is related to the host adaptation except for one barley-adapted strain that showed characteristics of wheat-adapted strains and one wheat-adapted strain which did not produce septorines.