Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), is a serious disease

of cotton in Australia responsible for substantial yield reductions. Since its detection on the

Darling Downs in 1993, Fov has spread to all major eastern cotton growing districts except

the lower Namoi. The significant crop losses that have already occurred and the increasing

incidence and severity of Fusarium wilt make Fusarium wilt the most significant challenge

to long term sustainable cotton production in Australia.

Improved farm management strategies can reduce yield losses and disease spread, but

developing resistant cultivars is by far the most effective long-term means of combating

fungal diseases of agricultural plants. Australian cotton breeders have significantly

improved the Fusarium wilt resistance of their cultivars, and new selections with even

greater resistance are nearing commercial release. Despite the admirable progress that has

been made, however, the current assessment is that new sources of Fusarium wilt resistance

are needed.

With the realization that the best the G. hirsutum gene pool has to offer may not be good

enough, We have looked to related Australian Gossypium species for novel sources of

Fusarium wilt resistance, identifying one possible source of Fusarium wilt resistance in G.

sturtianum. Although some of the G. sturtianum accessions tested are susceptible to fusarium

wilt, many of the accessions are more resistant to fusarium wilt than the industry standards,

and this resistance is expressed in the G. hirsutum background. Genetic analysis of G.

hirsutum x G. sturtianum hybrids, however, suggests transferring the G. sturtianum genes to

G. hirsutum will be difficult. Nonetheless, breeding lines are currently in the Fusarium field

nurseries and this selection process will continue.

The other important outcome of this project was the development of new experimental

populations and molecular markers that will, in ongoing research, provide a much better

understanding the genetic control of fusarium wilt resistance in cotton. Under this grant,

five chromosomes of the G. sturtianum genome have been identified as carrying genes that

may contribute fusarium wilt resistance. The experimental populations and molecular

markers will contribute to a more explicit genetic understanding of Fusarium wilt resistance

that will facilitate our ability to effectively transfer genes from G. sturtianum as well as other

novel resistance sources. With the apparent lack of immunity in the G. hirsutum gene pool,

these novel germplasm resources will become increasingly important to cotton breeders.