Monday, October 12, 2009

New article: Population genetics and migration of P. ramorum

Goss, E.M.; Larsen, M.; Chastagner, G.A.; Givens, D.R.; and Grünwald, N.J. 2009. Population genetic analysis infers migration pathways of Phytophthora ramorum in US nurseries. PLoS Pathogens 5(9): e1000583.
Abstract: Recently introduced, exotic plant pathogens may exhibit low genetic diversity and be limited to clonal reproduction. However, rapidly mutating molecular markers such as microsatellites can reveal genetic variation within these populations and be used to model putative migration patterns. Phytophthora ramorum is the exotic pathogen, discovered in the late 1990s, that is responsible for sudden oak death in California forests and ramorum blight of common ornamentals. The nursery trade has moved this pathogen from source populations on the West Coast to locations across the United States, thus risking introduction to other native forests. We examined the genetic diversity of P. ramorum in United States nurseries by microsatellite genotyping 279 isolates collected from 19 states between 2004 and 2007. Of the three known P. ramorum clonal lineages, the most common and genetically diverse lineage in the sample was NA1. Two eastward migration pathways were revealed in the clustering of NA1 isolates into two groups, one containing isolates from Connecticut, Oregon, and Washington and the other isolates from California and the remaining states. This finding is consistent with trace forward analyses conducted by the US Department of Agriculture's Animal and Plant Health Inspection Service. At the same time, genetic diversities in several states equaled those observed in California, Oregon, and Washington and two-thirds of multilocus genotypes exhibited limited geographic distributions, indicating that mutation was common during or subsequent to migration. Together, these data suggest that migration, rapid mutation, and genetic drift all play a role in structuring the genetic diversity of P. ramorum in US nurseries. This work demonstrates that fast-evolving genetic markers can be used to examine the evolutionary processes acting on recently introduced pathogens and to infer their putative migration patterns, thus showing promise for the application of forensics to plant pathogens.

New research: Evaluating ornamentals as physical barriers between blocks of plants susceptible to Phytophthora ramorum

Shishkoff, N. 2009. Evaluating ornamentals as physical barriers between blocks of plants susceptible to Phytophthora ramorum, 2007-2008. Plant Disease Management Reports 3:OT029.

Assessing the potential of Silv-Exᆴ and Silv-Ex Plusᆴ to eradicate Phytophthora ramorum spores in water

Assessing the potential of Silv-Exᆴ and Silv-Ex Plusᆴ to eradicate Phytophthora ramorum spores in water - Based on two studies at UC Davis, using Silv-Ex® or Silv-Ex Plus® (foaming agent used in fire control) to treat water that is potentially infested with P. ramorum, greatly reduces, but does not eliminate, the concern for inadvertently spreading the pathogen through fire suppression efforts. For more information, contact Kamyar Aram at kamaram@ucdavis.edu.

Pierce county salal treated

The Washington State Department of Agriculture is working with the USDA Animal and Plant Health Inspection Service and Forest Service, as well as the State Department of Natural Resources and Pierce County, to mitigate the impacts of the previously identified P. ramorum-positive salal plants in a native landscape adjacent to a Pierce County retail nursery. The response will include remounting drainage ditches where the landscape finds were made and lining them with rock. This will prevent any future nursery runoff from coming in contact with susceptible P. ramorum hosts. The infected salal plants have been killed with herbicide, and the debris cleaned out of the ditches. For more information, contact Brad White at bwhite@agr.wa.gov.