Comparative mapping of Eucalyptus and Corymbia

The genus Corymbia is closely related to the genus Eucalyptus, and like Eucalyptus contains tree species that are important for sub-tropical forestry. Corymbia’s close relationship with Eucalyptus suggests genetic studies in Corymbia could benefit from transfer of genetic information from its more intensively studied relatives. Here we report a genetic map for Corymbia spp. based on microsatellite markers identified de novo in Corymbia sp (n=28) or transferred from Eucalyptus (n=117). A comprehensive consensus map was generated from an outbred F2 population created by crossing two Corymbia torelliana x citriodora subsp. variegata F1 trees. The map was composed of 55 microsatellite markers distributed across 12 linkage groups (LOD 3) and had a total length of 417 cM (Kosambi). A high proportion of Eucalyptus microsatellites (63%) transferred to Corymbia allowing a comparative analysis between our Corymbia map and published Eucalyptus maps. Synteny with a Eucalyptus grandis map was moderate and there was no strong evidence for chromosomal structural differences. Instances of non-synteny were associated with large distances on the Eucalyptus map and low power to detect linkage due to low genome coverage in Corymbia. Segregation distortion was primarily restricted to a single linkage group and due to a deficit of hybrid genotypes, suggesting that hybrid inviability shaped the genetic composition of the F2 population in this inter-subgeneric hybrid. The conservation of microsatellite loci and synteny between Corymbia and Eucalyptus suggests there will be substantial value in exchanging information between the two groups.