Reproduction of Symptoms of a Root Disease of Wheat by Toxic Metabolites Produced by Two Pythium Species and their Partial Characterization

Abstract Three Pythium isolates Pythium arrhenomanes isolates (320) & (323)], and Pythium irregulare produced in vitro metabolites that affect normal wheat seedling growth and development. P. arrhenomanes isolates (320 & 323) produced toxic metabolites that caused a general browning of root tissue of 2–3-day-old wheat seedlings, root stunting, inhibition of root hair formation, and reduced fresh and dry root weights. These symptoms were also seen in infected seedlings inthe field. Culture filtrates of P. irregulare only partly reproduced disease symptoms, as they inhibited root elongation, but did not cause any browning of root tissue or inhibition of root hair formation. P. irregulare filtrates also stunted shoot growth and stimulated root hair formation and elongation in a swollen area immediately behind the root tip. Autoclaving did not affect activity of P. irregulare culture filtrates, but did inactivate P. arrhenomanes culture filtrates, suggesting that they are different. Ultrafiltration separations of P. arrhenomanes (isolate 320) filtrates indicated that toxic metabolites were heterogeneous. One component was less than 1,000 mol.wt. and the other greater than 50,000 mol.wt., but less than 100,000 mol.wt.