Fusarium wilt continues to be an important constraint to sustainable cotton production. This project had a number of objectives to obtain data to improve the management of this disease.

Even though it has been dry, diseased samples suspected of being Fusarium wilt were still sent to DPI&F for analysis. A total of 252 diseased specimens have been examined during the course of the project from Qld and NSW. Of these 49% were positive for Fov, and of the positive specimens, 121 belonged to VCG 01111, which was the original strain identified from the Darling Downs, and two belonged to VCG 01112. There were some new recordings of Fov however the rate of reporting of new cases of Fusarium wilt has declined. The slower rate of reporting in recent years may reflect a combination of farm hygiene measures, decreased cropping area due to drought, and increased use of less-susceptible varieties. A new strain of the pathogen was detected in 2005 from the Macintyre valley. Sampling from the same area has not yielded further isolates of this type, indicating that this new isolate, which probably arose from a spontaneous mutation, has not spread. A new VCG code will not be designated to this new strain until a larger number of representative isolates are identified. A reference collection of preserved strains of Fov is being maintained at DPI&F laboratories at Indooroopilly. A data base, which includes all records of isolations of Fov made at the Indooroopilly laboratories is continually updated and is searchable under several fields such as, cotton variety, state, district or year.

Many of the current strategies to manage the disease have been developed as a result of the project work carried out at Graham Clapham’s property ‘Cowan’. The ‘Cowan’ trial site is recognised by the cotton industry as a high disease incidence site, providing unbiased information on disease management practices. Some specific outcomes include: (i) the identification of germplasm, with improved resistance to Fov, has been used in breeding program to provide new varieties with better resistance to Fusarium wilt, (ii) monitoring the reaction of varieties to Fov and development of a comparative varietal reaction guide has provided an independent disease assessment guide for growers, and (iii) the identification of some agricultural practices, such as crop rotations and residue management that may reduce the incidence of disease. The management strategies that have been developed have not increased pesticide usage.

There was no evidence in this study that non-pathogenic isolates of Fusarium oxysporum cross-protect cotton against Fov. Many of the isolates collected from cotton fields were actually root pathogens, although they were not vascular pathogens. Some isolates however were beneficial in reducing the effect of Pythium spp. on cotton. Silicon amendments were identified that reduced disease severity under glasshouse conditions when applied to field soil, but were not effective under field conditions. Application of high phosphorus significantly increased disease severity in glasshouse trials and requires further investigation.

The results from this project have had an impact on grower’s returns, value of properties, rural businesses and communities that service the cotton industry as well as processors and exporters. These results have been vital to plant breeders to assist them in producing less susceptible varieties. The research results obtained during this project have been widely disseminated throughout the industry.

A grower’s perspective of the impact of the research on disease management epitomises the value of this research. “The results of this research have played a major part of the success in slowing the rapid spread of Fusarium wilt that happened in the late 1990’s. By using the information obtained from the rotation trials and varieties with higher F rank, fields which have been unable to produce cotton for many years because of high Fusarium levels have returned economic yields in the past two seasons. Whilst we have come some distance in understanding this disease it still has the potential to cause serious crop losses given the right environmental circumstances. Therefore it is important to continue to screen new varieties and explore cropping practices that will halt its spread and enable production of cotton on highly infected fields again”.