Fusarium wilt of cotton is caused by Fusarium oxysporum Sclecht f. sp. vasinfectum (Atk.) Sny. and Hans (F.o.v.).  F.o.v. occurs in most countries where cotton is grown.  Losses in cotton yield can be especially devastating on farms where soil conditions, nematode populations, and indigenous populations of the pathogen favor the disease. 

A genetically unique strain of F.o.v. was first recognized in wilted and dead Upland cotton seedlings in Australia in 1993.  Since that time, the pathogen has spread rapidly despite strict containment practices.  On some Australian farms where it was first discovered, losses above 90% have forced cotton production to be abandoned.  The Australian strain was inadvertently introduced into the U.S. in at least two shiploads of cottonseed imported into California for cattle feed in 2001 and 2002.  We have calculated that each short ton of imported seed contained 17.6 million infected seed.  In 2001, 325,000 tons of cottonseed were imported into California from Australia.  The Australian F.o.v. strain is favored by heavy clay soils and does not require nematodes for severe disease.  Although the Australian biotypes have not yet been found in California cotton fields, its presence in imported cottonseed makes it a threat to >4 million acres of cotton grown on heavy alkaline soils in the U.S. from California to Texas.  There is also a treat to U.S. cotton production from highly pathogenic F.o.v. race 4 isolates that have been identified in California fields; these attack both Gossypium barbadense and G. hirsutum cottons, but the disease is particularly severe on the former.  Both the Australian biotype and the California race 4 isolates produce prodigious quantities of the phytotoxin fusaric acid.  This phytotoxin may play a critical role in the pathogenicity of these pathogens.  We have conducted biosynthetic studies using carbon-13 labelled sodium acetate and aspartic acid to determine how fusaric acid is synthesized in the pathogen.  Results of these studies will be presented.