| Sudden oak death (SOD) is a devastating disease of oak and tanoak in the western United States, caused by the non-native, generalist pathogen Phytophthora ramorum Werres et al. Quercus agrifolia Nee (CLO&;This research aimed to elucidate chemical mechanisms of resistance and identify factors that may affect the production of phenolic defenses in susceptible Quercus spp., including CLO and NRO, before and after infection with P. ramorum. Time was a significant explanatory factor for the variability of certain phenolics, both within and between years, though overall variation was low and did not appear to be related to variability in CLO susceptibility to P. ramorum. NRO treated with a known, phosphonate-based elicitor of host defenses, were more resistant to P. ramorum, and both constitutive and induced levels of certain phenolics were also significantly impacted.;Additionally, new approaches for identifying naturally resistant CLO based solely on constitutive concentrations of phenolics were tested. Four phenolic biomarkers of resistance were partially identified in CLO phloem collected before P. ramorum infection and were used to estimate the probability of CLO resistance and survival following infection with P. ramorum. Finally, this research demonstrated that Fourier-transform infrared (FT-IR) spectroscopy, combined with multivariate statistical analysis, can be used to distinguish between resistant and susceptible CLO prior to infection. The ability to identify resistant trees within forest stands could be a valuable tool for conserving and breeding resistant germplasm and identifying areas at risk of SOD. Moreover, the approaches utilized in these studies to identify resistant trees may be useful in other systems where forest pests and pathogens are of concern. |
