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Genetic diversity and population structure of the potential biocontrol agent, Valdensinia heterodoxa, and its host Gaultheria shallon (salal) Wilkin, Jennifer

Abstract

Valdensinia heterodoxa Peyronel is an ascomycete fungus currently being considered as a potential biocontrol agent for Gaultheria shallon Pursh. (salal). In order to design an effective biocontrol agent and to assess its effectiveness and risks, the population structure of both V. heterodoxa and salal must be investigated. Infected salal leaves were collected from three geographically separate populations on Vancouver Island and coastal mainland British Columbia. Uninfected salal was collected from two additional sites. V. heterodoxa was cultured from the infected leaves and single spore cultures were obtained prior to DNA isolation. Amplified fragment length polymorphisms (AFLPs) were used to generate individual DNA fingerprints for each isolate. Of the 214 loci analyzed, 30 % were polymorphic, suggesting low genetic diversity. There were many shared haplotypes within each population, and as expected, analysis of pairwise kinship coefficients showed that as spatial distance increased, genetic similarity decreased. Analysis of molecular variance (AMOVA) between populations revealed significant genetic differentiation between populations with an FST of 0.18, perhaps a result of limited gene flow. Salal DNA was isolated from leaf tissue and AFLPs were used to fingerprint individuals resulting in 230 loci, which were 89.7% polymorphic on average. Within population diversity was high, with an average observed heterozygosity of 0.49. In addition, due to the high ploidy level of salal (octoploid), the results obtained from the dominant AFLP markers likely underestimate the actual genetic diversity in the populations. Populations were poorly differentiated (FST 0.096 ) , suggesting high gene flow among populations. Within one population (Shawnigan Lake), genetic similarity decreased with increased geographic distance and showed little evidence of clonal population structure. ii When the genetic variation in V. heterodoxa was compared to that in salal, high correlations of alleles observed between the species suggest that different V. heterodoxa pathogenicity groups, or salal varieties with varying levels of susceptibility, could be contributing to the distribution of V. heterodoxa in these populations. Overall, the findings from the genetic analyses were used to discuss the potential risks of using V. heterodoxa as a biocontrol agent for salal and suggest that with low diversity and high population differentiation, the effectiveness of V. heterodoxa as a biocontrol may be limited to use within local salal populations or in combination with other control methods to effectively manage salal in forested areas.

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