Submitted to: Heredity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/10/2006
Publication Date: 8/16/2006
Citation: Edme, S.J., Glynn, N.C., Comstock, J.C. 2006. Genetic segregation of microsatellite markers in Saccharum officinarum and S. spontaneum. Heredity. 97:366-375. 2006. Interpretive Summary: Sugarcane is an important crop in the economy of South Florida and the US in general. Finding molecular or DNA markers associated with traits of economic importance is sought in the Canal Point sugarcane (Saccharum spp) breeding program for greater efficiency. The first step in reaching this goal consists of finding landmarks (markers) specific to the two parents involved in a cross by fingerprinting the progeny population. This study used the first generation of a cross between Green German (S. officinarum) and IND 81-146 (S. spontaneum) and microsatellites as the type of marker system. Markers were assembled into chromosomes where genes are located and the grouping of chromosomes constitutes a map. Two maps were so developed, one for each parent, which provide insight into the constitution of their genomes: 78% of the markers were inherited in a Mendelian (normal) fashion and 22% showed distortion particularly in the female parent. Distortion was both localized and random and a specific chromosome associated with segregation distortion was detected in the female (GG) genome only, probably as a result of double reduction. Other irregularities were also observed in the form of chromosome breakages, fusions, double reduction, and rearrangements, with involvement of the centromeres. The two parental maps covered 1204 cM on 27 chromosomes of the Green German genome and 664 cM on 10 chromosomes on the IND 81-146 genome. Although incomplete, these maps are a first step in assessing the contribution of both parents to sugar production and exploits these findings in marker-assisted breeding and selection.
Technical Abstract: Segregation of 193 microsatellite (SSR) loci was evaluated in the F1 progeny of a Saccharum officinarum (Green German or GG, 2n*11x*110) x S. spontaneum (IND 81-146 or IND, 2n*7x*56) interspecific cross. The purpose of this study was to dissect the structure of the parental genomes by typing 169 full-sibs of the cross. Following the two-way pseudo-testcross strategy and “cross pollination” population type, linkage groups (LG) and phases were established for each parent map with a log odds ratio (LOD) score * 3.0, a maximum recombination frequency of 0.35, and the Kosambi function. Of 193 markers analyzed, 61 and 106 were specific to the male and female parents, respectively, with 78% segregating in a Mendelian fashion and 22% showing distorted segregation as tested by *2-tests (P*0.05). The remaining 26 markers were heterozygous in both parents. The GG map included 91 marker-loci arranged into 27 LG covering 1204 cM of the officinarum genome. The IND map consisted of 46 marker-loci assembled into 10 LG which spanned 664 cM of the spontaneum genome. A specific chromosome associated with segregation distortion was detected in the female (GG) genome only, probably as a result of double reduction. The segregation patterns of the marker-loci indicated a centromere-driven process with the shared allelic markers (as putative centromeres) regulating the placement and association of markers with opposite phase (coupling vs. repulsion) and dosage on either side. Four homeologous groups (HG) were identified with a total of 50 single-dose markers and 27 double-dose markers. Although incomplete, the framework maps were informative with respect to segregation distortion, chromosome fusion, rearrangements, and translocations, observed in the parental genomes as a result of the merger.