Diagnostics and emerging plant pathogens

Accurate identification of plant pathogens is essential for making management decisions and determining appropriate regulatory actions. An accurate identification is facilitated when a group is well understood taxonomically based on robust systematics studies. Such studies provide information on which morphological and molecular characters are taxonomically useful and tools can then be developed to use in detection and identification. Identification of emerging plant pathogens poses a particular challenge in that they are often understudied and poorly characterized. Phytophthora ramorum, the causal agent of sudden oak death and ramorum blight, exemplifies how regulatory diagnostics evolve as scientific knowledge about the disease and its causal pathogen is gathered and evaluated. The discovery of new and related taxa, including P. foliorum that cross-reacted in the P. ramorum nested assay, led to the development of additional assays. The use of new markers to compare large numbers of P. ramorum isolates has provided a clearer picture of the genetic diversity in the pathogen and a means of tracing origins of newly found isolates. This case study is one of many examples of the importance of a strong understanding of the systematics of a group as the basis for accurate identification and the development of diagnostic tools.