In a cool, wet season when conditions are favourable for the Verticillium dahliae fungal pathogen, Verticillium wilt disease can cost the Australian cotton industry millions of dollars in lost production. The susceptibility of cotton plants to Verticillium wilt does however vary between cotton species and cultivars (Ramsay et al, 1996), and breeders have attempted to select cotton germplasm with increased resistance to the disease. True resistance can be found in cultivars of Gossypium barbadense, such as the American cultivar Pima S-7, whereas cultivars of Gossypium hirsutum at their best only display tolerance to the disease, restricting the development of disease symptoms and allowing the production of a reasonable crop. Plant breeders from the CSIRO have now developed several G. hirsutum cultivars with increased tolerance to Verticillium wilt such as Sicala V-I, Sicala V-2 and Siokra V-15