Relationships Among Vegetative Compatibility Groupings, Toxin Production, and Virulence of Fusarium oxysporum to Cotton

More than 1200 isolates of Fusarium oxysporum obtained from cotton were used in a series of studies over 20 years.  These isolates were obtained from wilted plants, roots of plants without symptoms, and live seed imported into the U.S.A.  In some cases, the isolates were associated with severe damage from root knot or reniform nematodes. Various isolates including type specimen of races 1-6, were obtained from culture collections and other research scientists.  The virulence of all isolates to “Rowden” cotton was determined in stem-puncture assay.  Virulent isolates and a random collection of 20 avirulent isolates were then studied in more detail.  Virulence to various cotton cultivars and other crops, vegetative compatibility based on nit mutants and toxin production profiles were determined.  Results of these studies and our conclusions about variability in F. oxysporum pathogens of cotton will be presented.