Submitted to: Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2006
Publication Date: 6/1/2007
Citation: Wu, Y., Huang, Y. 2007. An SSR genetic map of Sorghum biocolor (L.) Moench and its comparison to a published genetic map. Genome. 50:84-89. Interpretive Summary: The development of methods to analyze DNA sequence differences or polymorphism, permitted the construction of a map of the whole genome from one single population. Such genetic maps provide an interpretation of the distribution of genes along chromosomes and show the location of genes on chromosomes and the distances between them. A new genetic linkage map was recently developed for sorghum using simple sequence repeat (SSR) markers. Here we report the construction of a sorghum genetic map based on 118 SSR markers mapped on 277 F2 individuals from our mapping population with a new genetic background. These mapped SSR loci were distributed throughout 10 chromosomes of sorghum and spanned a distance of 997.5 cM. More importantly, 38 SSR loci were newly added to the sorghum genetic map in this study. In addition, a novel method was developed for calculating distance between DNA markers on chromosomes. Using this method, we compared our map with a previously published sorghum map based on map positions of common loci, which provided a strong support for the alignment of two genetic maps. Thus, it proved to be a useful tool for comparative analysis of genetic markers between linkage maps with different genetic background and alignment of different sorghum genetic maps. This new genetic linkage map also provides a set of useful DNA markers that is transferable across different mapping populations and will allow the identification and comparison of the most important regions involved in the variation of the traits of interest and the development of marker-assisted selection for sorghum breeding. The map has added value in gene isolation by map-based cloning strategies.
Technical Abstract: Sorghum bicolor (L.) Moench is an important grain and forage crop grown worldwide. We developed a simple sequence repeat (SSR) linkage map for sorghum using 352 publicly available SSR primer pairs and a population consisting of 277 F2 individuals derived from a cross between the Westland A line and PI 550610. One hundred thirty-two (132) SSR loci appeared polymorphic in the mapping population, and 118 SSRs were mapped onto 16 linkage groups. These mapped SSR loci were distributed throughout 10 chromosomes of sorghum and spanned a distance of 997.5 cM. More importantly, 38 SSR loci were newly added to the sorghum genetic map in this study. The mapping result also showed that chromosomes SBI-01, 02, 05 and 06, each had one linkage group, while the other six chromosomes were composed of two linkage groups each. Except for five tightly linked marker flips and one locus Sb6_34, the marker order of this map was collinear to a published sorghum map, and the genetic distances of common marker intervals were similar with a difference ratio less than or equal to 0.05 between the two maps. The difference ratio is a new index developed in this study that can be used to compare the genetic distances of DNA markers between two maps. This SSR map carrying additional SSR markers will facilitate mapping quantitative trait loci to the sorghum genome and map-based gene cloning. Furthermore, the novel method for calculating distance between DNA markers will be a useful tool for comparative analysis of genetic markers between linkage maps with different genetic background and alignment of different sorghum genetic maps.