Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/29/2004
Publication Date: 5/26/2004
Citation: Gao, W., Clancey, J.A., Han, F., Jones, B., Budde, A.D., Wesenberg, D., Kleinhofs, A., Ullrich, S. 2004. Fine mapping of a malting-quality qtl complex near the chromosome 4h s telomere in barley. Theoretical and Applied Genetics. 109:750-760. Interpretive Summary: The entire barley genome has been mapped and malt-quality traits have been assigned to chromosome regions. This manuscript describes marker assisted crosses and analyses that were performed to fine map malt-quality traits to a defined chromosomal region. Use of molecular markers in that region should have great utility for future marker assisted breeding to generate new barley varieties having improved malting quality.
Technical Abstract: Malting quality has long been an active objective in barley breeding programs. However it is difficult for breeders to manipulate malting quality traits because of inheritance complexity and difficulty in evaluation of these quantitative traits. Quantitative trait Locus (QTL) mapping provides breeders a promising basis with which to manipulate quantitative trait genes. A malting-quality QTL complex, QTL2, was mapped previously to a 30-cM interval in the short-arm telomere region of barley chromosome 4H in a ‘Steptoe/Morex’ doubled haploid population by the North American Barley Genome Project, using an interval mapping method with a relatively low-resolution genetic map. The QTL2 complex has moderate effects on several malting-quality traits, including malt extract percentage (ME), alpha-amylase activity (AA), diastatic power (DP), malt beta-glucan content (BG), and seed dormancy, which makes it a promising candidate gene source in malting barley-cultivar development. Fine mapping QTL2 is desirable for precisely studying barley malting-quality trait inheritance and for efficiently manipulating QTL2 in breeding. A reciprocal-substitution mapping method was employed to fine map QTL2. Molecular marker-assisted backcrossing was used to facilitate the generation of isolines. Fourteen different types of ‘Steptoe’ isolines, including regenerated ‘Steptoe’ and 13 different types of ‘Morex’, were made within a 41.5-cM interval between MWG634 and BCD265B on chromosome 4H. Duplicates were identified for 12 ‘Steptoe’ and 12 ‘Morex’ isoline types. The isolines together with ‘Steptoe’ and ‘Morex’ were grown variously at three locations in 2 years for a total of five field environments. Four malting-quality traits were measured: ME, DP, AA, and BG. Few significant differences were found between duplicate isolines for these traits. A total of 15 putative QTL’s were mapped; three for ME, four for DP, six for AA, and two for BG. Of the 15 QTL’s identified, ten were from the ‘Morex’ and only five from the ‘Steptoe’ background. By combining the results from different year, field environments, and genetic segments, six QTL’s can be conservatively estimated: two each for ME and AA and one each for DP and BG with chromosome segments ranging from 0.7-cM to 27.9-cM. A segment of 15.8-cM from the telomere (MWG634-CDO669) includes all or a portion of all QTL’s identified. Further study and marker-assisted breeding should focus on this 15.8-cM chromosome region.