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Physical mapping methods that do not rely on meiotic recombination are necessary for complex polyploid genomes such as wheat (Triticum aestivum L.). This need is due to the uneven distribution of recombination and significant variation in genetic to physical distance ratios. One method that has proven valuable in a number of nonplant and plant systems is radiation hybrid (RH) mapping. This work presents, for the first time, a high-resolution radiation hybrid map of wheat chromosome 1D (D genome) in a tetraploid durum wheat (7: turgidum L., AB genomes) background. An RH panel of 87 lines was used to map 378 molecular markers, which detected 2312 chromosome breaks. The total map distance ranged from ~3,341 [cR.sub.35,000] for five major linkage groups to 11,773 [cR.sub.35,000] for a comprehensive map. The mapping resolution was estimated to be ~199 kb/break and provided the starting point for BAC contig alignment. To date, this is the highest resolution that has been obtained by plant RH mapping and serves as a first step for the development of RH resources in wheat.

The compatibility-inducing action of the sc[s.sup.ti] (species cytoplasm-specific gene derived from Triticum timopheevii) and Vi (vitality) genes can be observed when a durum (T. turgidum) nucleus is placed in T. longissimum cytoplasm. These two genes restore compatibility between an otherwise incompatible nucleus and cytoplasm. The objective of this study was to localize the sc[s.sup.ti] gene on a linkage map of chromosome 1A, which could eventually be used to clone the gene. The mapping population consisted of 110 [F.sub.2] individuals derived from crossing a Langdon-T. dicoccoides chromosome 1A substitution line with a euplasmic (normal cytoplasm) line homozygous for the sc[s.sup.ti] gene. Through a series of testcrosses the genotypes of the 110 individuals were determined: 22 had two copies, 59 bad one copy, and 29 had no copy of the sc[s.sup.ti] gene. Data from RFLP, AFLP, and microsatellite analysis were used to create a linkage map. The flanking marker loci found for the sc[s.sup.ti] gene were Xbcd12 and Xbcd1449-1A.2 with distances of 2.3 and 0.6 cM, respectively. Nearly 10% of individuals in this population were double recombinant for a genetic interval of

Few genetic male sterility (GMS) genes have been mapped in hexaploid wheat (Triticum aestivum L.). Our objective was to locate to chromosomes the GMS genes in mutants FS2, FS3, FS20, and FS24. We crossed each mutant to the Cornerstone male sterile, which has the ms1c allele, to determine allelic relationships. We crossed the FS20 mutant to `Chris' monosomics, and observed segregation in the [F.sub.2] and backcrosses to FS20. After observing the results, we made appropriate crosses to Chinese Spring (CS) ditelosomic lines to locate and map the genes to chromosome arms. The allelism test to Cornerstone indicated that the mutants FS2, FS3, and FS24 were allelic to ms1. In the monosomic analysis of the mutated FS20 gene, half of the monosomic 3A plants were male sterile. Therefore, the mutated gene in FS20 was located in chromosome 3A. This conclusion was confirmed by analyzing segregation ratios in backcross populations involving chromosome 3A. The FS20 mutant was crossed with CS ditelosomic 3AS and 3AL, and the monotelodisomic 3AS plants were male sterile. Therefore, the FS20 gene was in chromosome arm 3AL. A backcross of monotelodisomic 3AL plants to FS20 was used to map the mutated gene in FS20 relative to the centromere. The linkage chi-square test indicated that the FS20 gene was not linked to the centromere of chromosome 3A. The gene symbol ms5 was assigned to the mutated gene in FS20, and gene symbols ms1d, ms1e, and ms1f were assigned to the mutations in FS2, FS3, and FS24, respectively., MALE STERILITY may be conditioned by either cytoplasmic specific or genetic (chromosomal) male sterility (GMS) genes. Cytoplasmic male sterility has been more extensively studied than GMS for hybrid wheat production. [...]

A number of recombination-based and physical mapping methods have been developed in order to study and understand the genomic organization of plant species. Of these methods, physical mapping methods provide the best correlation between position on a map and actual physical location on the chromosome. In this review, we discuss differences between maps developed on the basis of recombination and those developed independent of recombination. In the latter method, termed commonly as physical mapping, we discuss methods that have been employed in a number of agriculturally important plant species including rice, the legume model Medicago, tomato, soybean, barley and wheat, and then focus on the radiation hybrid method of physical mapping. After a brief overview of the radiation hybrid methods employed in mammalian species, we discuss radiation hybrid mapping for maize, barley, cotton and wheat in detail. [ABSTRACT FROM AUTHOR]