Agriculture Reference
In-Depth Information
Although the earliest studies in cereals focused on the candidate gene
approach, in more recent years a signi
cant number of GWA studies
have been developed for barley (Kraakman et al. 2004; Comadran et al.
2009; Cockram et al. 2010), maize (Szalma et al. 2005), rice (Agrama et al.
2007; Iwata et al. 2009; Yan et al. 2009a; Huang et al. 2010), and wheat
(Neumann et al. 2010). The number and types of traits studied have
varied greatly. These include simpler traits such as production of maysin
and chlorogenic acid in maize (Szalma et al. 2005) as well as broader
agronomic traits. More complex traits have included kernel size and
milling quality in wheat (Breseghello and Sorrells 2006), stigma and
spikelet characteristics in rice (Yan et al. 2009a), as well as grain yield
and yield components in barley and rice (Agrama et al. 2007; Cockram
et al. 2010). In the last 2 years, a number of AM studies have been
completed for cereals, especially for barley, using Illumina SNP sets
made several years in advance. One interesting study by Pasam et al.
(2012) looked at a relatively simple morphological trait for two-rowed
versus six-rowed spike formation in barley as a way to evaluate the
sensitivity of GWA. The use of a single 1536 SNP chip detected over 100
associations, half of which con
rmed previously identi
ed QTL. In
another barley study by Locatelli et al.
(2012), growth habit and
in
orescence type were studied in a mini core collection using candi-
date genes and over 4,000 SNPs. They followed initial association
analysis with con
rmation of associations in larger germplasm sets of
more than 2,000 genotypes using a subset of the SNPs. A recent study in
rice looked at associations with grain color, phenolic content,
flavonoid
content, and antioxidant capacity in dehulled rice (Shao et al. 2011),
showing that novel traits can be rapidly assessed with this approach.
In summary, most association studies in cereals have started with
oligo- or multigenic traits of moderate heritability. This was the case in
Breseghello and Sorrells (2006) that looked at seed size and processing
quality in wheat, in Szalma et al. (2005) that looked for maysin accu-
mulation in maize silks for insect resistance, or in Stracke et al. (2009)
that looked at
flowering time in barley. Some cereal studies have
achieved a high level of detail with up to 14 agronomic traits analyzed
in rice by Huang et al. (2010). Grain yield QTLs across 60 experiments
were studied with GWA approach in wheat by Crossa et al. (2007). Two
other landmark AM studies involved more than 800 wild accessions of
the maize progenitor
Teosinte and phenotyped for over a dozen archi-
tectural traits using polymorphism in candidate genes (Weber et al.
2007, 2008). Other studies have dealt with yield traits in barley
(Kraakman et al. 2004), but more recent studies have focused on yield
component traits (Locatelli et al. 2012; Pasam et al. 2012).
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