Population Structure and Dynamics Among Fusarium oxysporum Isolates Causing Wilt of Cotton

From 1990 to 2005 more than 2,000 isolates of Fusarium oxysporum and closely related species were obtained from diseased cotton plants, cotton field soils, or other investigators.  The pathogenicity of these isolates to cotton was determined by stem-puncture, root dip, and soil infestation assays.  Genetic relationships among virulent isolates were determined by vegetative compatibility tests and DNA sequence analyses of partial genes.  The results of these studies will be presented and interpreted in terms of increasing losses from Fusarium wilt and the need for new sources of resistance effective against all populations of F. oxysporum.