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Abstract
Quantifying the growth rates of plant pathogens in the laboratory can be useful for predicting rates of disease spread and impact in nature. The purpose of this study was to examine phenotypic variation among isolates of
Phytophthora ramorum collected from a foliar host plant species,
Umbellularia californica (California bay laurel), naturally-occurring in localities in three regions (southwest, east, northwest) in a 275 km
2 study area in Sonoma County. These regions differ topographically, in history of infection by
P. ramorum, and in microclimate and plant community composition.
We quantified phenotypic variation among
P. ramorum isolates among regions, plots, and individual trees, allowing us to detect host-plant effects on
P. ramorum phenotype, and to detect geographic structure in phenotypic characteristics. It also allowed us to test the hypothesis that North American isolates of
Phytophthora ramorum show relatively high levels of phenotypic variation despite their low levels of genetic variation.
Isolates were collected in spring 2006, after a relatively wet period favorable to
P. ramorum growth. Growth of 37 different isolates, one or two per tree, from 25 California bay laurel trees from 15 plots was measured on V8 agar plates at four different temperatures (16, 20, 24, 26°C). Each plate was scanned five times over 12 days (day 2, 5, 7, 9, 12). Colony diameter was quantified at each time point using image analysis software (NIH Image). Change in colony diameter over time was analyzed using linear regression of diameter versus day. Growth was linear through day 12 for all replicates, allowing us to estimate growth rate using the slope from each regression. We used growth rate (slope value) and olony size (diameter at day 12), as dependent variables in analyses with region, plot, tree, and isolate as nested grouping factors that were crossed with the grouping factor of treatment temperature in a mixed model analysis of variance.
Parent Publication
Citation
Sherron, Valerie; Rank, Nathan E.; Cohen, Michael; Anacker, Brian L.; Meentemeyer, Ross K. 2008. Spatial variation in effects of temperature on Phenotypic characteristics of
Phytophthora ramorum isolates from eastern Sonoma county. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 447-448
