High throughput development of population genetic markers for the Sirex noctilio woodwasp and its nematode parasite, Deladenus siricidicola

Abstract

Sirex noctilio is a major pest to Pinus spp. and threat to the Forestry industry in the Southern Hemisphere. The varying level of efficacy of its primary biological control agent, Deladenus siricidicola, is also of serious concern. There is a need to better understand the diversity of both the pest and its biological control agent, as one of the factors that could influence this biological control system. One of the short‐comings is that molecular markers did not exist to study the population diversity of the nematode and wasp. As part of this study it was illustrated how next generation sequencing (454 pyrosequencing) can be used to enhance microsatellite marker discovery tools, and produce a more robust, rapid and economical tool for the development of these markers. The developed markers for D. siricidicola and S. noctilio proved to be highly efficient in characterizing the population diversity of both of these organisms.It was shown that the populations of D. siricidicola in the Southern Hemisphere is highly homozygous at all the loci developed, which likely resulted from human selection of favorable strains, genetic bottlenecks during transfer and subsequent inbreeding. This result likely suggested a reduced ability of the nematode to adapt to the diverse environmental conditions, different Pinus spp. and S. noctilio populations found in the various regions. The populations from Southern Hemisphere and Canadian sources were distinct at most loci and illustrate the unexplored potential of exploring diverse populations of D. siricidicola in order to screen for useful phenotypic variation. The microsatellite markers that were developed were also effectively used to characterize representative samples of S. noctilio in the Southern Hemisphere. The alleles are largely shared amongst countries, reflecting the shared history of introduction. It also shows a stepwise invasive process in South Africa, leading to a genetic bottleneck which might have a significant impact on the population ecology of the wasp, as it can influence its sex ratio. This thesis contributes critical tools and knowledge necessary to understand the population diversity of both D. siricidicola and S. noctilio. As argued in the final chapter, this information and the use of these tools in future is critical to understand aspects such as the evolution of virulence and population ecology of the organisms, which should be used to direct biological control programs.