Title: Genetic diversity of Phytophthora ramorum in Belgium
Author: Vercauteren, Annelies; De Dobbelaere, Isabelle; Maes, Martine; Heungens, Kurt;
Source: In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M. 2010. Proceedings of the Sudden Oak Death Fourth Science Symposium. Gen. Tech. Rep. PSW-GTR-229. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 110-113
Publication Series: General Technical Report (GTR)
Description: Phytophthora ramorum is thought to be an introduced pathogen in North America and in Europe based on the presence of only three clonal lineages. The North American lineages (NA1 and NA2) are responsible for infections in North American forests and nurseries, while the European lineage (EU1) is responsible for infections in Europe, mostly in nurseries. There have also been a few isolated findings of the EU1 lineage in North American nurseries. P. ramorum is heterothallic, with two opposite mating types, A1 and A2. The A1 mating type was originally only found in Europe, with the exception of three A2 isolates of the EU1 lineage collected in Belgium in 2002 and 2003. Although there is no evidence for sexual reproduction in nature, the presence of both mating types at a single site might lead to genetic recombination.
To verify the hypothesis of asexual reproduction in nature, and to verify the hypothesis that P. ramorum was recently introduced in Belgium and therefore possesses only a limited amount of genetic diversity, the Belgian P. ramorum population was screened with AFLP and SSLP markers. Use of the AFLP method with five primer combinations on a selected number of isolates (80) revealed 13 polymorphic fragments. These markers identified eight isolates that differed from the main genotype by one to three polymorphisms. Use of SSLP with existing microsatellite markers revealed a limited number of polymorphisms in the EU1 population. Additional microsatellite markers were then sought. A total of 146 candidate polymorphic microsatellites were prescreened using 10 isolates belonging to different EU1 genotypes. This resulted in two new primer pairs that amplify a total of three polymorphic loci, of which one was very useful. Seven markers (four existing and three new) were used to screen all 411 Belgian isolates. In total, 30 genotypes were identified, but 68 percent of the isolates belong to the main genotype EU1MG1. Although indications of accumulated mutation events were present, the overall level of genetic diversity within these isolates of P. ramorum appears to be limited, indicating a relatively recent clonal dispersion of the pathogen. Most of the genotypes were site-specific and some of them were detected over a period of several years at a single site, sometimes discontinuously. This indicated (latent) survival of the pathogen at those sites and led to questions about the efficiency of the eradication measures. No marker recombination was observed, indicating that no sexual recombination was found in nature.
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Vercauteren, Annelies; De Dobbelaere, Isabelle; Maes, Martine; Heungens, Kurt. 2010. Genetic Diversity of Phytophthora ramorum in Belgium. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M. 2010. Proceedings of the Sudden Oak Death Fourth Science Symposium. Gen. Tech. Rep. PSW-GTR-229. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 110-113
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