Agriculture Reference
In-Depth Information
In maize, recent research has switched to a more controlled exercise in
AM with nested association mapping(NAM) populations (Poland et al.
2011; Kump et al. 2011; Tian et al. 2011). Multiparent advanced genera-
tion intercross (MAGIC) population derived from four elite cultivars has
been used in wheat as a novel method for
finding trait associations
(Huang et al. 2012). SNP identi
cation by GBS methods is also expected
to accelerate the
field of association genetics and mapping (Elshire et al.
2011).
B. Dicotyledenous Crops
Fewer AM studies have been undertaken on dicotyledenous crops,
although signi
cant studies are available on the plant model
Arabidop-
sis thaliana
(Table 2.3). The more advanced genetic and genomic tools
and state of the art in cereals (and
Arabidopsis
) vis-à-vis many dicoty-
ledenous crop species explain this situation. In addition, cereals are
usually easier to manage agronomically than legumes, vegetables, and
roots or tubers, which will be the main subject of this part of the chapter.
Among the tropical and subtropical species of major interest are many
of the dicotyledenous crops. Two plant families, the Leguminoseae
(Fabaceae) and the Solanaceae, stand out for their importance as con-
taining species that are basic staples. With a few exceptions in vegetable
species, these staple food crops of tropical origins will be the topic of the
rest of this section. We will also mention the potential for work on some
related root crops such as cassava, sweet potato, and yams.
Among the
first group of crop species of interest is the large and
diverse legume family with representative cultivated species from
almost every continent and every center of origin for crop diversity.
The neotropical legume, common bean, has been a valuable target for
GWA studies because of its extensive genetic diversity (Blair et al. 2009).
However, the divided population structure for the species has made it
necessary to consider genepools as separate subgroups for AM. GWA
studies in common bean have been carried out with up to 606 genotypes
but considering the species as a whole. When evaluating more related
germplasm, 183 genotypes have been used (Shi et al. 2011). Although
four other
Phaseolus
species are cultivated, no association studies have
been realized with the wild relatives.
Another important legume genus includes the
Vigna
species. Among
these, cowpea has recently received a large addition of genetic markers
that has allowed preliminary AM to be carried out. Unlike common
bean, cowpea does not have the same levels of population structure and
may have lower levels of LD. Asparagus bean, another
Vigna
species, has
