Phytotoxicity of metabolites produced by 'Pyrenophora semeniperda' in liquid culture

'Pyrenophora semeniperda' was shown to produce heat stable, biologically active metabolites under agitated liquid culture conditions. Using a seedling bioassay it was shown that filtrates harvested from 'P. semeniperda' cultures had a significant impact on coleoptile length of both wheat and Bromus diandrus, but had no effect on seed germination. The relative toxicity of filtrates derived from several isolates of 'P. semeniperda' and infiltrated into wheat leaves was highly correlated with the virulence of these isolates. A comparison of metabolites harvested from 'P. semeniperda' and Pyrenophora teres grown under the same cultural conditions revealed that 'P. teres' did not affect wheat coleoptile growth, but affected the coleoptile elongation of 'B. diandrus', although less than filtrates produced by 'P. semeniperda'. Culture filtrates harvested after 6 days were toxic to wheat and 'B. diandrus' and toxicity was maximal in filtrates derived from cultures that were 12 days old. Culture filtrates diluted to 1 in 20 produced symptoms in wheat seedlings, but only undiluted or 5 × concentrated filtrates produced symptoms on 'B. diandrus' seedling leaves. Plants older than first node stage (Z 31) were significantly less sensitive to filtrate than younger plants. A degree of host selectivity to the metabolites was observed since leaves of 'Gossypium hirsutum', 'Helianthus annuus', 'Lablab purpureus' and 'Xanthium occidentale' were unaffected by infiltrates.