Agriculture Reference
In-Depth Information
are more sustainable in low-input production. Participatory breeding pro-
grams have traditionally relied on low-cost, low-technology techniques,
due to the lack of resources and the involvement of the scientifi c com-
munity, at large. However, the understanding of their potential for sustain-
able agriculture and global resource savings should foster more funding
of these programs to allow the use of more effective breeding approaches.
The use of molecular markers has been implicated as a quite possible av-
enue to breed varieties with superior genotypes, when phenotypic selec-
tion becomes unreliable [65]. Marker assisted selection (MAS) uses ge-
netic markers or specifi c genetic sequences that have been determined to
be associated with known locus linked to a desired trait. This technique
is costly at fi rst as favorable genomic regions (QTLs) are identifi ed, but
it saves time thereafter. After QTLs have been detected, closely linked
markers can be used to trace, transfer and accumulate (trait pyramidation)
the valued genetic regions into one superior genotype at a much faster
speed than conventional breeding [65]. This particular method is also ad-
vantageous in low-input breeding because varieties can be further devel-
oped without recurrent fi eld evaluations and during off-season, since it is
based on linkage of the trait of interest with genomic regions revealed by
the markers that are correlated with better performance, allowing for the
quicker development of varieties. It is possible that current varieties, land-
races, or heirlooms will serve as starting material or genotype, and that
molecular markers will be used to transfer desired genetic segments from
other genotypes in order to develop elite varieties specifi cally aiming for
low-input production systems.
Although MAS has been key in developing modern varieties, it has
primarily been successful in manipulating a few traits controlled by major
effect genes [160]. Unfortunately this method has been insuffi cient when
improving polygenic or quantitative traits that are controlled by several
small effect genes [160]. A relatively new method, genome-wide or ge-
nomic selection has been developed to overcome the limitations of MAS.
Genomic selection is a form of MAS that calculates breeding values by
simultaneously analyzing all markers and phenotyping across an entire
genome [161]. These scores can then be applied to model parameters used
to estimate the value of future breeding lines with only marker data [160].
In addition this technique can be used without prior knowledge of marker
