|Vercauteren, A -|
|DE Dobbelaere, I -|
|Bonants, P -|
|Van Bockstaele, E -|
|Maes, M -|
|Heungens, K -|
Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 19, 2009
Publication Date: November 30, 2009
Citation: Vercauteren, A., De Dobbelaere, I., Grunwald, N.J., Bonants, P., Van Bockstaele, E., Maes, M., Heungens, K. 2009. Clonal expansion of the Belgian Phytophthora ramorum populations based on new microsatellite markers. Molecular Ecology. 19:92-107. Interpretive Summary: Phytophthora ramorum, causal agent of sudden oak death on oaks and ramorum blight on ornamentals, exists as a clonal lineage in Europe commonly referred to as EU1. While all isolates sampled in Europe belong to the A1 mating type, the A2 mating type has only been observed in Belgium, begging the question whether sexual reproduction is occurring. A collection of 411 Belgian P. ramorum isolates was established during a seven year survey. Our main objective was to determine population structure, evolution and spread. We used previously and newly developed molecular markers. Eighty isolates of P. ramorum broadly representing the Belgian population were analyzed. Thirty unique genotypes were identified, but 68% of the isolates belonged to the main genotype EU1MG1. Based on our analysis there is no evidence of sexual recombination in the Belgian population of P. ramorum.
Technical Abstract: Coexistence of both mating types A1 and A2 within the EU1 lineage of Phytophthora ramorum has only been observed in Belgium, begging the question whether sexual reproduction is occurring. A collection of 411 Belgian P. ramorum isolates was established during a seven year survey. Our main objective was the genetic characterization of this population to test for sexual reproduction, determine population structure, evolution and spread, and evaluate the effectiveness and impact of control measures. Three polymorphic SSR markers were developed after screening 149 candidate primer pairs. Eighty isolates of P. ramorum broadly representing the Belgian population were analyzed using four previously described and the three newly identified polymorphic microsatellite loci and AFLP. SSR analysis was most informative and used to screen the entire Belgian population. Thirty multilocus genotypes were identified, but 68% of the isolates belonged to the main genotype EU1MG1. Although accumulated mutation events were detected, the overall level of genetic diversity within the Belgian isolates of P. ramorum appears to be limited, indicating a relatively recent clonal expansion of the pathogen. Based on our SSR analysis, there is no evidence of sexual recombination in the Belgian population of P. ramorum. Metalaxyl use decreased the genetic diversity of P. ramorum until 2005, when the majority of the isolates had become resistant. Most genotypes were site-specific, and despite systematic removal of symptomatic and neighbouring plants, some genotypes were detected over a period of several years at a single site, sometimes discontinuously, indicating (latent) survival of the pathogen at those sites.