Fusarium wilt, caused by Fusaritim oxysporum f. sp. Vasinfectum (Fov), is a devastating disease in many cotton-producing countries of the world. In Australia, this disease, found first in 1993, has become a serious problem, occurring in most major cotton-growing regions and causing substantial losses (Kochman 1995). It is attributable to two genotypes of Fop; each of which belongs to a distinct vegetative compatibility group, VCGs 11 and 12, respectively (Bentley et al. 2000). Not only are the two Australian Fov strains different from the overseas Fov races in DNA fingerprints, but they have unique aesculin hydrolysis and volatile characteristics, implying that they were not introduced (Davis et al. 1996; Bentley et al. 2000)