A project investigating the molecular and histological effects of silicon application on cotton infected with Fov was inspired by promising preliminary results obtained by Dr Linda Smith (QPl&F) in glasshouse and field trials. Silicon application has been demonstrated to effectively ameliorate or reduce the symptoms of disease caused by fungal pathogens in many plant-pathogen interactions, including those involving host species such as rice, cucumber and wheat. The mechanisms of resistance attributed to silicon treatment include the creation of a physical barrier to pathogen penetration, and the induction of defence responses associated with the increased production of defence related compounds and alterations in defence gene expression. The feasibility of applying silicon to reduce incidence or severity of Fusarium wilt in cotton was investigated utilising two forms of silicon and two cotton cultivars with different resistances to Fov. The following defence responses were assessed with and without silicon treatment:

a. Disease severity and incidence, effect of silicon on nutrient acquisition

b. Histological defence reactions including the accumulation of phenolic compounds and lignin

c. Defence gene changes

d. Defence enzyme activity

As Bion has recently been registered for use by the Australian cotton industry, an additional aim of the project was to ascertain the effects of this chemical resistance inducing agent on cotton infected with Fov. Bion is applied to cotton seed as a seed treatment for the control of both Fusarium wilt and black root rot, whilst it is also commonly applied as a foliar spray to induce defence responses in other plant species. The aim of this research was to determine if defence responses in Fusarium wilt infected cotton, including defence gene expression changes and changes in the activities of defence related enzymes, were affected by Bion treatment; and to determine if these responses were more pronounced following Bion application in the form of a seed treatment or a foliar spray.