Barley for Food and Health: Science, Technology, and Products

40 BARLEY BIOTECHNOLOGY: BREEDING AND TRANSGENICS
tribe Triticeae was the stimulus to geneticists to obtain hybrids between barley
and wheat. Little success was achieved in this area until 1973, when it was
demonstrated that diploid H. vulgare L. could be crossed as a maternal parent
with diploid, tetraploid, and hexaploid wheat (Kruse 1973). Numerous combinations
of barley × wheat crosses have since been developed (Fedak 1992).
Wheat–barley recombinant lines are projected to provide useful supplementary
information for mapping of the barley genome, including further understanding of
genome organization and evolution in these two cereals. Interest in barley–wheat
hybrids is also directed toward translocation of specific genetic traits into barley
from wheat, or reciprocally, wheat traits into barley, providing the potential of
creating a new cereal such as triticale, which was produced by crossing durum
wheat with rye.
Molecular Markers
Molecular marker–assisted selection (MAS) is a laboratory approach to barley
breeding whereby chromosomal regions (loci) controlling particular traits of interest
can be identified and followed in a selection program. Effective use of this
technique in breeding demands the construction of chromosome linkage maps
and association of unique biochemical markers that are associated with different
alleles at these loci. In some cases, loci associated with traits can be associated
with a particular gene or genes, but the method can be used effectively,
even with no information about the gene or genes, as long as they are linked
genetically to the biochemical marker used for selection. There are significant
limitations to MAS for the selection of complex quantitative traits. Interactions
between large numbers of potential alleles at a large number of loci controlling a
trait make MAS more suitable for single traits or those controlled by only a few
genes. Certain aspects of disease resistance and quality are good candidates for
MAS, especially those that are difficult or expensive to phenotype (P. Bregitzer,
personal communication).
Molecular mapping of the barley genome began in the 1980s (Kleinhofs
et al. 1988), and since that time, extensive data have been generated by numerous
researchers that have permitted the development of detailed barley chromosome
linkage maps. The biotechnology leading to the mapping of the barley genome
was facilitated by the development of molecular markers, double haploids, availability
of numerous mutants, intergeneric crosses, and insert libraries (Kleinhofs
and Han 2002). The North American Barley Genome Project (NABGP) is a continuing,
multi-institutional, multidisciplinary project that has developed extensive
germplasm and molecular resources for genetic mapping, gene isolation, and gene
characterization in barley. Core mapping populations and specialized germplasm
resources allow NABGP researchers to place thousands of markers on genetic
maps (CRIS USDA 2007). The Barley Coordinated Agricultural Project (Barley
CAP 2007) is also a group effort currently composed of 30 or more barley
researchers from 19 institutions with expertise in genetics, genomic, breeding,
pathology, databases, computer science, food science, malt quality, and statistics.