The effects of sub-toxic levels of phosphonate on the metabolism and potential virulence factors of Phytophthora palmivora

Abstract

Potassium phosphonate (phosphite) altered the metabolism of P. palmivora in liquid cultures even under conditions where growth of the fungus was not restricted. However, under these conditions, the composition of the lipid and cell wall material was altered, as were the standing concentrations of intermediary metabolites (e.g. amino acids). The compound dehydroabietic acid, a diterpenoid, was detected as part of a neutral/cationic macromolecule in young Phytophthora mycelium. In the presence of phosphonate, this compound was absent. These changes in fungal metabolism and in the composition of the cell wall complex suggest a mechanism by which phosphonate may reduce the virulence of the pathogen in the host plant and consequently expose it to the natural host defences at an earlier stage of the invasion processes. Under the experimental conditions used, the fungus was able to reduce intracellular levels of phosphonate to levels below detection during the exponential growth stage. As phosphonate concentrations within the fungus fell, the number of metabolic changes observed in the fungus were also reduced.