Growing concern in recent years about the effects of pesticides and fungicides on the environment has led to an increased interest in alternative plant protection methods worldwide. Enhancing plants' own natural defence systems in order to provide broad spectrum resistance against a range of fungal, viral and bacterial pathogens is an attractive and viable alternative. The process, known as Systemic Induced Resistance (SIR), requires prior exposure of the plant to a locally infecting pathogen, an avirulent form of a pathogen or special chemicals. This exposure results in a 'sensitisation' of the plant leading to a rapid resistance response on subsequent pathogen attack. The protection thus provided in both treated and distal tissues is usually in the form of decreased lesion numbers or disease severity.