Studies on inheritance of fertility are of great importance in wheat breeding. Although substantial progress has been achieved in molecular characterization of male sterility and fertility restoration recently, little effort has been devoted to female sterility. To identify the gene(s) controlling female sterility in wheat efficiently, an investigation was conducted for the seed setting ratio using a set of F2 populations derived from the cross between a female sterile line XND126 and an elite cultivar Gaocheng 8901. Bulked segregation analysis (BSA) method and recessive class approach were adopted to screen for SSR markers potentially linked to female fertility gene loci in 2005. Out of 1080 SSRs in wheat genome, eight markers on chromosome 2D showed a clear difference between two disparate bulks and small recombination frequency values, suggesting a strong linkage signal to the sterility gene. Based on the candidate linked markers, partial linkage maps were constructed with Mapmaker 3.0 (EXP) instead of whole genome maps, and quantitative trait locus (QTL) mapping was implemented with software QTLNetwork 2.0. A major gene locus designated as taf1, was located on chromosome 2DS. The above result was confirmed by the analysis for 2007 data, and taf1 was identified on the same chromosome 2DS with a confidence interval of 2.4 cM, which could explain 44.99% of phenotypic variation. These results provided fundamental information for fine mapping studies and laid the groundwork for wheat fertility genetic studies.

We present a cost-effective DNA pooling strategy for fine mapping of a single Mendelian gene in controlled crosses. The theoretical argument suggests that it is potentially possible for a single-stage pooling approach to reduce the overall experimental expense considerably by balancing costs for genotyping and sample collection. Further, the genotyping burden can be reduced through multi-stage pooling. Numerical results are provided for practical guidelines. For example, the genotyping effort can be reduced to only a small fraction of that needed for individual genotyping at a small loss of estimation accuracy or at a cost of increasing sample sizes slightly when recombination rates are 0.5% or less. An optimal two-stage pooling scheme can reduce the amount of genotyping to 19.5%, 14.5% and 6.4% of individual genotyping efforts for identifying a gene within 1, 0.5, and 0.1 cM, respectively. Finally, we use a genetic data set for mapping the rice xl(t) gene to demonstrate the feasibility and efficiency of the DNA pooling strategy. Taken together, the results demonstrate that this DNA pooling strategy can greatly reduce the genotyping burden and the overall cost in fine mapping experiments.

The recessive mutation of the XANTHA gene (XNT) transforms seedlings and plants into a yellow color, visually distinguishable from normal (green) rice. Thus, it has been introduced into male sterile lines as a distinct marker for rapidly testing and efficiently increasing varietal purity in seed and paddy production of hybrid rice. To identify closely linked markers and eventually isolate the XNT gene, two mapping populations were developed by crossing the xantha mutant line Huangyu B (indica) with two wild type japonica varieties; a total of 1,720 mutant type F 2 individuals were analyzed for fine mapping using polymorphic InDel markers and high dense microsatellite markers. The XNT gene was mapped on chromosome 11, within in a fragment of *100 kb, where 13 genes are annotated. The NP_001067671.1 gene within the delimited region is likely to be a candidate XNT gene, since it encodes ATP-dependent chloroplast protease ATP-binding subunit clp A. However, no sequence differences were observed between the mutant and its parent. Bioinformatics analysis demonstrated that four chlorophyll deficient mutations that were previously mapped on the same chromosome are located outside the XNT region, indicating XNT is a new gene. The results provide useful DNA markers not only for marker assisted selection of the xantha trait but also its eventual cloning.

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