Tom Blake, Corresponding Secretary
North American Barley Genome Mapping Project
Participants in the North American Barley Genome Mapping Project (NABGMP) convened at Bozeman, MT, August 10-11 to evaluate the project's progress and determine future direction.
NABGMP is an organization of U.S. and Canadian scientists with the shared objective of understanding the relationship between barley's genotype and its phenotype. The original objective of the project was to construct a 10cM map of the barley genome and to use the map to identify and locate gene-controlling traits of economic importance, including yield, adaptation, malting and nutritional quality, and pest and disease resistance.
NABGMP is unique in that it is a multi-institutional, missionoriented project that involves scientists from numerous institutions and disciplines. The project has attracted support from Federal grants; commodity boards; and malting, brewing and feeding organizations in both the United States and Canada. In the United States, Federal funding has been garnered through a CSRS "Special Grant"; in Canada, Federal funding has been provided through the Natural Sciences and Engineering Research Council.
Accomplishments
Thus far, objectives of the project have been pursued through the use of doubled haploid lines derived from a cross between Steptoe and Morex, representatives of the two major spring 6-rowed barley germplasm groups. Doubled haploids from a second cross (Harrington x TR306) between 2-rowed parents are now in evaluation. Steptoe and TR306 are varieties that lack useful malting quality; however, they do have agronomic properties that Morex and Harrington lack. In the next year, doubled haploids from a cross between Morex and Harrington will permit a comparison of the genetic underlying malting quality in 2-rowed and 6-rowed germplasm bases.
At the Bozeman meeting, Dr. Andy Kleinhofs presented an overview of the mapping progress in the Steptoe/Morex cross. In this cross, 295 markers have been mapped (Fig. 1 shows a skeletal map). Complete maps have been submitted to Theor. Appl. Genetics. The average distance between markers is 4.2cM. Six centromeres and five telomeres have been located on the map. While the average map density exceeds the objectives, six gaps greater than 20cM remain. The largest gaps remain on chromosome 7 (2 gaps) and chromosome 4 in the region of the ml-o locus.
The gaps may represent physically small regions of high recombination. Physically large regions of low frequency recombination were also observed. The nucleolar organizers, the sites for the 26s and 18s ribosomal RNA genes, have long been known to reside at the secondary constriction on chromosomes 6 and 7. These are located approximately a chromosome arms' length from the centromere on each chromosome. Nonetheless, the recombinational distance between the centromere of chromosome 6 and NOR is 12cM. For chromosome 7, the distance between centromere and NOR is 2cM.
The quality and utility of the Steptoe/Morex map will be tested by transferring well-spaced markers to the Harrington x TR306 map. NABGMP barley maps will be merged with barley maps constructed in Germany by adding selected markers from our maps to the German maps and vise versa.
Nomenclature remains a problem. Due to our collaborative effort, the nomenclature used by NABGMP is uniform, but, in several cases, it differs from that being used in Europe. In the hope of reducing future confusion, an international committee has been organized to attempt to standardize barley gene map nomenclature. Drs. Pat Hayes and Ben Liu reported on quantitative trait analyses performed on replicated field and malt quality data gathered from testing sites in Oregon, Washington, Idaho, and Montana, using software designed by Drs. Ben Liu and Steve Knapp at Oregon State University.(fig. 2). GMENDEL and QTL-STAT provided an integrated software package, which developed linkage maps identical to MAPMAKER, and QTL analyses, which estimated both genotype effects and genotype-by-environment interaction. The ability of QTL-STAT to handle data from multiple environments and to provide nonlinear estimates of gene effects appeared to be a significant improvement over its predecessors. Major genes that modify yield, quality, and related traits were identified. When a "best possible" progeny genotype was synthesized from the data, it showed an estimated agronomic profile dramatically better than anything grown in the western United States and quality slightly better than Morex.
Future Efforts
While all well-designed genome mapping projects will produce both basic information and information of direct commercial value, maintenance of the tie between application and basic research was deemed critical to future success. Over the next 5 years, NABGMP will emphasize both basic (map construction and saturation of regions, genome location, and map-based gene cloning) and applied (QTL analysis, selection experiments, and technology simplification) research.
Future work on mapping includes expanding the Steptoe/Morex map to reduce gaps, adding morphological markers, and merging maps with maps produced by other projects. Maps suitable for QTL analysis will be developed with the Harrington/TR306 and Morex/Harrington crosses. Expansion of the mapped germplasm pool will take place along with development and utilization of YAC libraries, fine structure analyses of disease resistance loci, and QTL-based selection experiments.
The work already accomplished with barley demonstrates the value of this species as a model genetic system for the cool season grasses. Participants in the project look forward to transferring these technologies to other economically important grasses.