New approaches to assess coast live oak resistance before infection by the invasive pathogen Phytophthora ramorum
A. O. CONRAD (1), L. Rodriguez-Saona (1), B. McPherson (2), D. Wood (2), P. Bonello (1). (1) The Ohio State University, Columbus, OH, U.S.A.; (2) University of California, Berkeley, Berkeley, CA, U.S.A.
Coast live oak (<i>Quercus agrifolia</i>, CLO), an endemic species in coastal California forests, is highly susceptible to the invasive pathogen <i>Phytophthora ramorum</i>, the causal agent of sudden oak death (SOD). While putatively resistant CLO have been observed, there are few methods for identifying resistant trees and most rely on symptom expression following infection. The objectives of this study were to determine if CLO resistance and survival can be assessed pre-infection using (1) phloem phenolic biomarkers and (2) Fourier transform infrared (FT-IR) spectroscopy of phloem phenolic extracts combined with chemometric analysis. Phloem was collected from trees prior to inoculation with the pathogen, and symptom development and survival were monitored following infection. Constitutive phenolic biomarkers were significant predictors of survival (Cox Proportional Hazards, <i>P </i>= 0.048; Weibull survival analysis, <i>P </i>= 0.015). Analysis of FT-IR spectral data by soft independent modeling of class analogy identified two spectral ranges, associated primarily with carbonyl groups, which could discriminate between resistant and susceptible CLO before infection. Identification of resistant CLO in the landscape may be useful for protecting areas at risk of becoming affected by SOD or in breeding resistant germplasm. Furthermore, these new approaches for identifying resistant trees could be useful for the study and management of other emerging forests diseases and pest infestations.
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