Maize Starch for Industrial Applications - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 182

and trade-offs for simultaneous selection for multiple genes require consideration
of specific systems and resource availabilities; however the potential to eliminate
environmental effects on amylose content and remove laboratory sampling error
provides compelling reasons to employee MAS.
As with all marker projects, economics of cost must be considered, and row
costs, quantitative laboratory costs, and marker costs must be balanced. The
continuing evolution of reduced laboratory costs, not only in genomics but in
spectrophotometry, proteomics, and data analysis, continues to change the equilib-
rium of breeder formulae and facilitates new avenues of germplasm evaluation and
advancement.
Use of Haploids
Haploid breeding, prominently used in dent corn breeding, can be effectively
implemented with specialties. The relative cost to produce inbreds by use of
doubled haploids decreases as row costs and specialty trait evaluation and identi-
fication costs increase (Table 9.4 ).
The use of doubled haploids to facilitate single event backcross conversions is
not effective unless trait identification costs are very high. Waxy breeding is
probably best served by a marker-assisted selection program. Amylose, however,
where the recessive amylose-extender gene is expressed in combination with
potentially one to three modifiers, suggests a situation where a doubled haploid
approach would hold benefit. If there are five genes needed for top-end amylose
inbred development, using the F2 approach would require the evaluation of over
1,000 plants (40 nursery rows) and could potentially cost many more times as much
as using doubled haploids.
Many traditional breeding approaches for amylose inbred line development have
been used. Recurrent population development and pedigree line development are
likely much more effective approaches than F2 line selection; however, the major
advantages of haploid breeding are still apparent. Homozygous lines are obtained
quickly, genetic recombination is maximized, environmental error is reduced, and a
smaller number of individuals are needed for gene pyramiding. The major difficulty
in using doubled haploids is the requirement of specialized labor and knowledge to
perform the technique and limited access to inducer genetics. Outsourcing doubled
haploid line generation can provide a convenient and economical solution for many
specialty breeding programs.