Chemistry of coast live oak response to Phytophthora ramorum infection

Since the mid 1990s, Phytophthora ramorum has been responsible for the widespread mortality of tanoaks, as well as several oak species throughout California and Oregon forests. However, not all trees die, even in areas with high disease pressure, suggesting that some trees may be resistant to the pathogen. The apparent resistance to P. ramorum infection of some individuals within coast live oak populations has been observed in artificial inoculation studies. For example, from artificial branch-cutting inoculation trials, Dodd and others (2005) found significant variation (up to eightfold difference in lesion sizes) in susceptibility to P. ramorum. In addition, apparent resistance has also been observed in naturally infected forests, where a number of coast live oaks have survived for more than seven years despite being infected (McPherson and others 2005 and unpublished data).