Abstract
In this study we evaluated the role of plant defence pathways in resistance to Phytophthora cinnamomi by testing the susceptibility of mutants of Arabidopsis thaliana impaired in various defence pathways to P. cinnamomi infection. Susceptibility to infection was assessed by measuring the number of callose papillae, production of hydrogen peroxide, and measurements of pathogen biomass using quantitative PCR. Mutants impaired in the salicylic acid, jasmonic acid, ethylene, and phytoalexin camalexin pathways did not show increased susceptibility to P. cinnamomi compared to their wild type background Col‐0. However, the aba2 mutant deficient in abscisic acid (ABA) signalling displayed a very much higher level of susceptibility than the wild type parent, Col‐0. The results show that resistance of A. thaliana to P. cinnamomi is mediated by the ABA signalling pathway.