A new semi-dwarfing gene identified by molecular mapping of quantitative trait loci in barley.

Semi-dwarfing genes have been widely used in spring barley (Hordeum vulgare L.) breeding programs in many parts of the world, but the success in developing barley cultivars with semi-dwarfing genes has been limited in North America. Exploiting new semi-dwarfing genes may help in solving this dilemma. A recombinant inbred line population was developed by crossing ZAU 7, a semi-dwarf cultivar from China, to ND16092, a tall breeding line from North Dakota. To identify quantitative trait loci (QTL) controlling plant height, a linkage map comprised of 111 molecular markers was constructed. Simple interval mapping was performed for each of the eight environments. A consistent QTL for plant height was found on chromosome 7HL. This QTL is not associated with maturity and rachis internode length. We suggest the provisional name Qph-7H for this QTL. Qph-7H from ZAU 7 reduced plant height to about 3/4 of normal; thus, Qph-7H is considered a semi-dwarfing gene. Other QTLs for plant height were found, but their expression was variable across the eight environments tested.

Saturation and comparative mapping of the genomic region harboring Hessian fly resistance gene H26 in wheat.

Resistance gene H26, derived from Aegilops tauschii Coss., is one of the most effective R genes against the Hessian fly [Mayetiola destructor (Say)], an important pest of wheat (Triticum aestivum L.). Using a limited number of PCR-based molecular markers a previous study mapped H26 to the wheat chromosomal deletion bin 3DL3-0.81-1.00. The objectives of this study were to saturate the chromosomal region harboring H26 with newly developed PCR-based markers and to investigate the collinearity of this wheat chromosomal region with rice (Oryza sativa L.) and Brachypodium distachyon genome. A population of 96 F(2) individuals segregating at the H26 gene locus was used for saturation mapping. All wheat ESTs assigned to the deletion bin 3DL3-0.81-1.00 were used to design STS (sequence tagged site) primers. The wheat ESTs mapped near H26 were further used to BLAST rice and B. distachyon genomic sequences for comparative mapping. To date, 26 newly developed STS markers have been mapped to the chromosomal region spanning the H26 locus. Two of them were mapped 1.0 cM away from the H26 locus. Comparative analysis identified genomic regions on rice chromosome 1 and Brachypodium Super contig 13 which are collinear with the genomic region spanning the H26 locus within the distal region of 3DL. The newly developed STS markers closely linked to H26 will be useful for mapped-based cloning of H26 and marker-assisted selection of this gene in wheat breeding. The results will also enhance understanding of this chromosomal region which contains several other Hessian fly resistance genes.