Does phosphate affect the efficacy of the fungicide phosphite in controlling Phytophthora cinnamomi in Banksia Grandis?

Phytophthora cinnamomi isolates vary in their sensitivity to phosphite. In vitro studies of the Murdoch Phytophthora collection have identified phosphite tolerant and sensitive isolates (I). The in vitro work of Griffith et al. (1993) found that phosphite sensitive Phytophthora palmivora isolates were inhibited at all phosphate concentrations, whereas tolerant isolates were only inhibited when phosphate was limiting. The aim of the current study was to investigate the interaction of phosphate and phosphite in planta. The ability of these two isolates to colonise Banksia grandis stems at four levels of phosphate, sprayed with 0 and 0.5% was assessed.