Resistance, tolerance and competence for Phytophthora cinnamomi

Résumé 0

The outcome of host-pathogen interactions depends on host defensce and pathogen infection strategies. On the host side, two strategies, resistance and tolerance, have long been identified. They differ in their underlying mechanisms and their effects on pathogens. However, the dynamics of disease transmission also rely on host competence. This trait, defined as the ability of the host to allow pathogen transmission, is rarely studied for pathogen-supporting plants. We assessed the competence for Phytophthora cinnamomi of seedlings of five Quercus and one Castanea species and studied how this trait is correlated with resistance and tolerance. P. cinnamomi is responsible for the chestnut ink disease, alongside with Phytophthora x cambivora which has a much less generalist behaviour. Each seedling was inoculated in mini-rhizotrons by root-mycelium contact and phenotyped for its resistance, tolerance and competence. The amount of necrosis (lesion length), the effect of infection on plant performance (root growth) and the sporangia number were measured. Moreover, we developed a ddPCR assay to quantify the pathogen within host tissues near the inoculation point. This measure was used as a proxy of pathogen load. We were thus be able to assess relate individual host competence reported to the pathogen content measured in the same root fragment. No significant correlation between the phenotyped traits was found at the individual level. However, at the species level, the least competent species (Q. robur, Q. petraea) proved to be the most resistant. These results may have important implications for management of chestnut and oak ecosystems threatened by ink disease.