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Triticeae Genomics and Genetics 2012, Vol.3, No.2, 9
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has already been shown to be responsible for some
white-grained PHS tolerant genotypes in common
wheat (CN19055: Ogbonnaya et al., 2008; AUS1408:
Mares et al., 2005). We also know that MQTL 8
involved 7 original QTL for PHST and 4 original QTL
for dormancy. Therefore, it is apparent that dormancy
may affect PHS tolerance and vice versa. From
information available in Table 2, it is also obvious that
MQTL 8 has the highest
R
2
value explaining more
than 25% of the phenotypic variation (with a range of
8.0
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45.10), suggesting that this is a major QTL and
can be exploited for marker-assisted selection (MAS).
2.5 Important genomic region/QTL for PHST/
dormancy on other chromosomes
During last two decades, QTL (including both minor
and major QTL) for PHST have been mapped on all
wheat chromosomes, although most of these are minor
QTL with low PV. For instance, chromosome of
homeologous group 3 (3A, 3B and 3D) and chromo-
some 4A have been shown in several studies to carry
major QTL, although some major QTL have also been
identified on other wheat chromosomes including the
following: 1A (Singh et al., 2010); 2B (Munkvold et
al., 2009); 4B, 7D (Rasul et al., 2009); 5D (Fofana et
al., 2009) and 7A (Singh et al., 2010). These QTLs are
also notable because these are independent of seed
coat colour and can be utilized in breeding program
with a purpose to develop PHS tolerant genotype with
white seed coat colour. Despite this, these chromo-
somes could not be included during present study,
since adequate number of QTLs on each of these
chromosomes was not available. In future the
availability of more QTLs for PHST/dormancy on
these chromosomes may facilitate meta-analysis to
identify important genomic regions for PHST/
dormancy on these chromosomes.
2.6 Relationship between PHST and dormancy
PHST and seed dormancy are two related, but perhaps
independent economic traits, Physiology and bioche-
mistry of these traits has been studied in the past, but
the biochemical pathways involved are not fully
understood (Kulwal et al., 2011). In earlier studies,
grain dormancy has been shown to contribute to
enhanced resistance to pre-harvest sprouting (Mares et
al., 2009; Osa et al., 2003; Nakamura et al., 2007;
Lohwasser et al., 2005; Torada et al., 2005;
Ogbonnaya et al., 2008; Singh et al., 2010; Chen et al.,
2008; Mares et al., 2005; Kottearachchi et al., 2008;
Imtiaz et al., 2008; Munkvold et al., 2009; Rasul et
al., 2009; Fofana et al., 2009). This observation is
confirmed by the results of the present study showing
clustering of individual original QTLs for PHST and
grain dormancy into a single cluster during meta-QTL
analysis. QTLs for PHST measured as sprouting index
(Rasul et al., 2009; Fofana et al., 2009; Imtiaz et al.,
2008), visually sprouted seed (Imtiaz et al., 2008), GI
(Imtiaz et al., 2008; Munkvold et al., 2009; Rasul et
al., 2009; Fofana et al., 2009) and the associated trait
grain colour (Groos et al., 2002; Fofana et al., 2009)
were also clustered together and represented different
MQTLs. As mentioned earlier, this is either due to a
pleiotropic effect of individual QTL or due to
occurrence of closely linked genes for different traits.
2.7 PHST and grain colour
The demand for white-grain wheat has increased in
many domestic and international markets, particularly
in Southeast Asia and the Middle East, Africa and
North America (Ambalamaatil et al., 2006). However,
red-grain wheat appeared to be more tolerant to PHS
than white-grain wheat genotypes and/or is associated
with high seed dormancy. However, rarely red-grain
commercial cultivars have been found to be pre-harvest
susceptible and some white-grain
aestivum
and durum
wheat have been found to be PHS tolerant (Mares and
Ellison, 1990; McCaig and DePauw, 1992; Clarke et
al., 1994) suggesting no absolute association between
PHST and red grain colour.
The genetic dissection of PHST through QTL analysis
also led to successful use of markers linked with
PHST in backcross breeding for improvement of
PHST in common wheat (Kumar et al., 2010).
However derived lines produced using MAS in these
studies were red-grained. Therefore, efforts in our
laboratory are currently underway for production PHS
tolerant wheat genotypes with amber grain.
2.8 Candidate genes for dormancy/PHST and
MQTLs
The genomic regions containing MQTLs were also
examined for the presence of candidate genes for
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