Extreme homozygosity in Southern Hemisphere populations of Deladenus siricidicola, a biological control agent of Sirex noctilio

Abstract

The woodwasp Sirex noctilio, together with its mutualistic fungal symbiont Amylostereum areolatum, is the most damaging invasive pest of Pinus spp. in the Southern Hemisphere. The nematode Deladenus siricidicola parasitizes S. noctilio larvae and is the most effective biological control agent against this woodwasp. Nothing is known regarding the genetic diversity of D. siricidicola, even though such knowledge would be invaluable in improving sustainable biological control programs. The aim of this study was to develop microsatellite markers to study the genetic diversity of D siricidicola populations. Microsatellite enrichment was performed using Fast Isolation by AFLP of Sequences Containing repeats (FIASCO) and fragments were then sequenced using 454 GS-FLX pyrosequencing. From the 1.2 megabases of sequence data, 166 microsatellite containing contigs were identified. Twenty-six primer pairs were designed using the web-based program Primer3 and screened for polymorphism in populations of the nematode from different sources in the Southern Hemisphere. Seventeen primers amplified microsatellite-containing loci of interest. No length polymorphism was present in any of the microsatellite repeats in these populations. Regions flanking the microsatellites also showed no polymorphism, except for one transition observed in an Argentinean strain for locus Ds316. Twelve of the loci showed polymorphism between the Southern Hemisphere and Canadian sources of D. siricidicola. The lack of diversity in Southern Hemisphere populations of D. siricidicola could affect the ability of this nematode to adapt to different environments and host types where it is used in biological control programs, and should thus be considered as a factor in future control strategies and research projects.