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Triticeae Genomics and Genetics 2012, Vol.3, No.2, 9
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PHST and dormancy. It is known that wheat group 3
chromosomes, which are the largest in physical size
(Dvorak et al., 1984; Gill et al., 1991) are also the
most conserved in gene content and order (Munkvold
et al., 2004). This group also shared synteny with
barley (
Hordeum vulgare
L.) chromosome 3H (Devos
and Gale, 1993; Nelson et al., 1995), rye (
Secale
cereale
L.) chromosome 3R (Devos et al., 1992), rice
(
Oryza sativa
L.) chromosome 1 (Devos et al., 1992;
Ahn and Tanksley, 1993; Kurata et al., 1994; Van
Deynze et al., 1995b), maize (
Zea mays
L.) chromo-
somes 3 and 8 (Van Deynze et al., 1995b; Wilson et al.,
1999), sorghum (
Sorghum bicolor
L.) chromosome 3
(Whitkus et al., 1992; Klein et al., 2003), and diploid
oat (
Avena spp
.) chromosomes C and G (Van Deynze
et al., 1995a). At least 38 genes affecting morphological
and biochemical traits are located (Munkvold et al.,
2004) on this group. Among the more important genes,
Vp1
(VIVIPAROUS
-
1: dormancy-related) orthologues
have been cloned and sequenced in maize as
Vp1
(McCarty et al., 1991), in wheat as
taVp1
(Bailey et al.,
1999), in rice as
osVp1
(Hattori et al., 1994), in wild
oat
Avena fatua
, as
afVp1
(Jones et al., 1997), in
sorghum as
Sbvp1
(Carrari et al., 2001), and in
Arabidopsis thaliana
as
ABI3
(Koornneef et al., 1989).
In wheat
taVp1
has been shown to be located on the
long arms of group 3 chromosomes (genetic length
~97 cM) at a distance of ~30 cM from centromere
(Bailey et al., 1999). In the present study, chromo-
somes 3A, 3B and 3D measured ~175 cM, ~165 cM
and ~80 cM respectively as against the length of
~97 cM that was used for long arm of group 3
chromosomes in Bailey’s study. Comparative study
for the position of
taVp1
between Bailey’s map and in
the consensus map used in the present study indicate
that ~30 cM distance in the earlier map of group 3
chromosomes corresponded to ~99 cM for 3A, ~97
cM for 3B and ~44 cM for 3D map used in the present
study. Interestingly, we noted that MQTL 2 (located at
96.48 cM), MQTL 5 (located at 96.41 cM) and MQTL
7 (located at 43.71) are located in the same regions,
where gene
taVp1
is located on chromosome 3AL,
3BL and 3DL respectively, making
taVp1
gene as
possible candidate gene for PHST/dormancy QTL.
In several earlier studies, QTL for PHST/dormancy
have also been detected on wheat chromosome 4AL
(Flintham et al., 2002; Kato et al., 2001; Mares and
Mrva, 2001; Mares et al., 2005; Chen et al., 2008;
Ogbonnaya et al., 2008; Rasul et al., 2009; Nakamura
et al., 2007; Singh et al., 2010; Lohwasser et al., 2005;
Munkvold et al., 2009; Imtiaz et al., 2008). In wheat
the three homoeologues of the
GA20
-oxidase gene
TaGA20
-
ox1
(involved in gibberellin biosynthesis,
controlling PHST/seed dormancy) have also been
mapped to chromosomes 5BL, 5DL and 4AL (Appleford
et al., 2006).
GA20
-
oxidase gene (encoding gibberellin
20 oxidase), mapped on the long arm (located in bin
4AL5
-
0.66
-
0.80) of barley chromosome 5H (Li et al.,
2004) has been considered to be a candidate gene for
dormancy and/or pre-harvest sprouting tolerance
(PHST). This region showed good synteny with
terminal end of long arm of rice chromosome 3 and
with the telomeric region of wheat chromosome 4AL.
However, this region was located outside the QTL
reported for seed dormancy in wheat on 4AL (Li et al.,
2004). On the basis of available markers, the most
likely position of the QTL for PHST/seed dormancy
was identified in bin 4AL12
-
0.43
-
0.59 on 4AL (Li et
al., 2004). When we compare this region with the 4AL
dense map of present study, it was found that MQTL 8
(located at 75.75 cM) was present in the same region,
thus suggesting the possibility of
GA20
-
oxidase gene
(
TaGA20
-
ox1
) to be a candidate for PHST/seed
dormancy on 4AL. However further work is needed to
investigate the potential relationship of
taVp1
with
MQTLs 2, 3 and 7 on long arm of group 3
chromosomes and of
TaGA20
-
ox1 with MQTL 8 on
long arm of 4A chromosome.
2.9 Genetic architecture of PHST and utility of
MQTLs for breeders
On the basis of meta-QTL analysis conducted during
the present study, the genetic architecture of PHST in
hexaploid wheat can be described as follows: (1) a
large number of QTLs on all the 21 wheat chromo-
somes control the quantitative trait PHST, (2) different
PHS tolerant genotypes in wheat may carry different
sets of QTLs, (3) only a few QTLs have large effects;
most other QTLs have small effects that are prone to
genotype ×environment interactions.
The present study also supports the view that PHST is
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