Genetic maps for Pinus elliottii var. elliottii and P. caribaea var. hondurensis using AFLP and microsatellite markers

Genetic maps for individual Pinus elliottii var elliottii and P caribaea var hondurensis trees were generated using a pseudo-testcross mapping strategy. A total of 329 amplified fragment length polymorphic (AFLP) and 12 microsatellite markers were found to segregate in a sample of 93 interspecfic F₁ progeny. The male P caribaea var hondurensis parent was more heterozygous than the female P elliottii var elliottii parent with 19% more markers segregating on the male side. Framework maps were constructed using a LOD 5 threshold for grouping and interval support threshold of LOD 2. The framework map length for the P elliottii var elliottii megagametophyte parent (1,170 cM Kosambi; 23 linkage groups) was notably smaller than the P caribaea var hondurensis pollen parent (1,658 cM Kosambi; 27 linkage groups). The difference in map lengths was assumed to be due to sex-related recombination variation, which has been previously reported for pines, as the difference in map lengths not be accounted for by the larger number of markers mapping to the P caribaea var hondurensis parent - 109 compared with 78 in P elliottii var elliottii parent. Based on estimated genome sizes for these species, the framework maps for P elliottii var elliottii and P caribaea var hondurensis covered 82% and 88% of their respective genomes. The pseudo-testcross strategy was extended to include AFLP and microsatellite markers in an intercross configuration. These comprehensive maps provided further genome coverage, 1,548 and 1,828 cM Kosambi for P elliottii var elliottii and P caribaea var hondurensis, respectively, and enabled homologous linkage groups to be identified in the two parental maps. Homologous linkage groups were identified for 11 out of 24 P elliottii var elliottii and 10 out of 25 P caribaea var hondurensis groups. A higher than expected level of segregation distortion was found for both AFLP and microsatellite markers. An explanation for this segregation distortion was not clear, but it may be at least in part due to genetic mechanisms for species isolation in this wide cross.