Construction of a high-density composite map and comparative mapping of segregation distortion regions in barley.

Segregation distortion can negatively impact on gains expected using selection. In order to increase our understanding of genetic factors that may influence the extent and direction of segregation distortion, segregation distortion analyses were conducted in four different doubled haploid (DH) populations. A high-density composite map of barley was then constructed by integrating information from the four populations. The composite map contained 2,111 unique loci, comprising RFLP, SSR and DArT markers and spanned 1,136 cM. In the four populations investigated, the proportion of markers with segregation distortion ranged from 15 to 38%, depending on the population. The highest distortion was observed in populations derived by the microspore culture technique. Distorted loci tended to be clustered, which allowed definition of segregation distortion regions (SDRs). A total of 14 SDRs were identified in the 4 populations. Using the high-density composite map, several SDRs were shown to have consistent map locations in two or more populations; one SDR on chromosome 1H was present in all four populations. The analysis of haplotypes underlying seven SDRs indicated that in three cases the under-represented haplotypes were common across populations, but for four SDRs the under-represented haplotypes varied across populations. Six of the seven centromeric regions harboured SDRs suggesting that genetic processes related to position near a centromere caused the segregation distortion in these SDRs. Other SDRs were most likely due to the methods used to produce the DH populations. The association of the SDRs identified in this study and some of the genes involved in the process of haploid production described in other studies were compared. The composite map constructed in this study provides an additional resource for the barley community via increased genome coverage and the provision of additional marker options. It has also enabled further insights into mechanisms that underpin segregation distortion.