Understanding and Managing Sudden Oak Death in California Genetic resistance—

Genetic differences between individual host plants appears to influence susceptibility to infections caused by P. ramorum. If sufficient levels of genetic resistance are present, it may be possible to select oaks and tanoaks with higher levels of resistance to P. ramorum for restoration of affected forests. Various researchers are actively investigating this area (e.g. Nagle and others 2011). Results from this research may have implications for long-term disease management strategies. As noted above ( Effects of tree size and condition), the age and physiological state of a tree can also influence its resistance to P. ramorum. An individual tree located in an infested forest that has no P. ramorum symptoms may or may not have genetic resistance to this pathogen. For instance, an individual that shows some resistance to P. ramorum infection under low inoculum levels might be fully susceptible under very high inoculum levels.