Abstract

Black root rot, caused by Thielaviopsis basicola, was observed on volunteer soybean (Glycine max) in August 2003 in a cotton field near Narrabri, NSW. Chlamydospores of T. basicola were observed on necrotic, dark-brown cortical tissue on the roots. The fungus was isolated and pathogenicity was confirmed. The isolate from soybean appeared to be more pathogenic on cotton (Gossypium hirsutum) than on soybean. Rotation with soybean may contribute to the carryover of T. basicola in cotton farming systems.