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

36 BARLEY BIOTECHNOLOGY: BREEDING AND TRANSGENICS
the introgression of disease resistance, for instance, and for isogenic analysis:
that is, the comparison of two alternate states (alleles) of a gene in an otherwise
homogeneous background in the same or nearly the same background genotype.
For example, isogenic lines contrasting six- and two-rowed spikes have
been developed and compared for agronomic and malt quality (Wiebe 1978).
Similarly, hulled and hulless isolines have been developed in several genotype
backgrounds to measure the influence of dietary fiber on the feed value of barley
(Hockett 1981).
Bulk handling is an efficient and inexpensive method to grow large numbers of
early cross-line generations. Selections are made and tested as individual lines at
the end of the scheduled breeding program. The bulk breeding system is adapted
to mass selection and is useful in identifying numerous phenotypic characteristics.
Composite crossing is a type of bulk breeding where a number of single
crosses are combined into a composite mixture, providing an efficient selection
method. When using the composite crossing technique, projected objectives are
generally long term in nature, allowing for recombination of many genes from a
broad-based germplasm (Anderson and Reinbergs 1985). A breeding technique
termed male-sterile-facilitated recurrent selection (MSFRS) was developed by
R. F. Eslick at the Montana State University and Agricultural Experiment Station.
When used in conjunction with the composite crossing technique, MSFRS
allows selected matings within composites to achieve specific breeding objectives
(Ramage 1975). A deviation of this method is the diallel selective mating system
(DSMS) proposed by Jensen (1970). In this system, simultaneous insertion of
multiple genotypes can be introduced into a few controlled populations. MSFRS
and DSMS facilitate broadening of the genetic base and break up existing linkage
blocks while providing greater genetic variability than is available in many other
breeding systems (Anderson and Reinbergs 1985).
Several widely used methods that may be considered as conventional barley
breeding programs include single-seed descent breeding (SSD) and pedigree
breeding (Tourte 2005). The SSD breeding method was proposed as a way to
maintain maximum genetic variation in self-pollinating species while obtaining
a high level of homozygosity. This method may be used for parental evaluation,
which is accomplished by evaluating an array of homozygous lines from
several crosses and identifying those crosses that have the highest proportion
of superior progeny. Pedigree breeding is best applied where genetic characters
are highly heritable and can be identified in early segregating populations but
not for characters with low heritability. Pedigree breeding is the most common
method employed for characters with complex inheritance, such as malting quality.
Breeders working within narrow germplasm pools regularly use pedigree
breeding–based methods, frequently in combination with the SSD method to get
many lines into advanced states of homozygosity without losing genetic variability.
A strong point of the pedigree system is the ease with which the planned
breeding can be modified at any stage of selection (Lupton and Whitehouse 1957).
Modification of the pedigree system as proposed by these authors provides for
yield estimates at the same time as line generations are being advanced.