Fusarium wilt disease has the potential to cause significant yield losses and the removal of some areas from cotton production. It is therefore likely to impact on the long-term sustainability of the cotton industry. Conventional breeding techniques have made some progress towards generating resistance to Fusarium wilt in the cotton plant, but breeding efforts would be enhanced by knowledge of the factors that contribute to resistance. In addition, knowledge of the factors controlling the pathogenicity of the pathogen could provide the basis for the development of novel techniques that allow minimisation of the impact of the disease.

Resistance to the wilt pathogens is complex and probably controlled by many genes. This makes the task of breeding for resistance complex and difficult. In order to determine suitable approaches for improving cotton’s resistance by breeding or by the use of genetic engineering, we need an improved understanding of the existing plant responses that are effective at giving some resistance to Fusarium wilt. Identification of the genes deployed by cotton during infection by the Fusarium wilt pathogen, particularly those associated with the response of more resistant species or cultivars, could indicate new targets for effective breeding or for manipulation by genetic engineering. In this project, we aimed to develop tools for the large-scale study of gene expression in cotton and Fusarium, and to apply these tools to investigate gene expression in the host and the pathogen during the infection process.

During the course of this project, we developed effective microarray and model infection systems for the analysis of gene expression in Fusarium-infected cotton. This is a resource of potential use to the cotton industry in the identification of potential targets for generation of improved resistance to Fusarium wilt.

The most striking observation made during analysis of gene expression patterns was that in infected seedlings, gene expression changes in roots and hypocotyls appear to be different.

We found that repression of gene expression, particularly repression of genes for water-regulating proteins, such as aquaporins, was consistently observed in roots and hypocotyls. This repression appears to be associated with susceptibility. This identifies aquaporins as potentially important in the development of wilt symptoms.

In the Fusarium wilt pathogen, expression of a homologue of the AtsC gene from Agrobacterium may be important for pathogenicity, and expression of the retrotransposon foxy may provide a mechanism for rapid adaptation, and hence pathogenicity evolution, in Fusarium populations.