Black root rot, caused by the pathogen Theilaviopsis basicola is an important disease in Australian cotton. Each season NSW DPI conducts surveys in commercial cotton crops to document the incidence and severity of cotton diseases. Currently there are 60 T. Basicola isolates in the long term culture collection as a result of isolating the pathogen from plants suffering symptoms. Black root rot does not generally kill plants but causes slow growing, stunted plants. The consequences of this is an uneven crop, maturity is harder to manage and pushes the crop back. This delay means the crop is slower to develop and increases the risk of a late maturing crop. This in turn has the potential to push the crop into cooler weather near the end of maturity, increasing the risk of Verticillium wilt disease.

The incidence and severity of black root rot has increased over the last decade, especially in the Namoi valley. The question is why? In order to answer this question we need to gain a better understanding of the pathogens morphology, growth rates and pathogenicity among isolates collected from different geographical regions within the production areas of NSW.