Abstract
Phosphite (H2PO3 ‐) is a phosphate analog widely used to protect plants from oomycete pathogens such as Phytophthora and Pythium. Phytophthora species are prominent pathogens in agriculture, e.g. Phytophthora infestans causing potato late blight. Phytophthora cinnamomi has devastating effects on native ecosystems with over 4000 plant species at risk in Western Australia alone. Phosphite is a well‐known protectant of plants and exhibits a complex mode of action. I It directly inhibits the pathogen’s growth by interference with its phosphate‐dependent metabolism. At the same time it also inhibits the plant’s phosphate starvation response, e.g. the up‐regulation of high‐affinity phosphate transporters, and thus has constrictive effects on plant growth under low phosphate supply. In addition to these direct effects, phosphite also induces the plant’s defence responses with increased expression of defence genes. However, the underlying mechanism of this indirect effect is not understood. We have started to characterise the impact of phosphite on plant defence responses by analyses of transgenic plants, metabolic pathways and the natural genetic variation in the plant Arabidopsis thaliana.