Efficacy of heat-based treatments in eliminating the recovery of the sudden oak death pathogen (Phytophthora ramorum) from infected California bay laurel leaves.

摘要

Phytophthora ramorum is the plant pathogen responsible for the lethal disease of several oak species in California, USA, known as sudden oak death. The pathogen also causes a foliar disease on Umbellularia californica (bay laurel or simply bay). Bay leaves have been identified as the major source of natural inoculum in California coastal woodlands. Because of the epidemiological relevance of bay leaves, their movement needs to be regulated. Our study shows that P. ramorum is highly heat tolerant and can be reisolated from artificially inoculated bay laurel leaves placed at 55 degrees C for up to one week. The pathogen cannot be recovered after 2 weeks at 55 degrees C. Prolonged heat treatments, however, are impractical for bay leaves intended to be sold commercially as a spice, since they negatively impact the quality of the leaves. Here, we describe a treatment involving a progressive and gradual heating process combined with the application of moderate vacuum. This method can be completed in 22 hours and is shown here to eliminate the recovery of P. ramorum without having a negative impact on the quality of the bay leaves.