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Molecular Plant Breeding 2013, Vol.5, No.9, 47
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53
Table 6 Quantitative trait loci QTL, identified in chromosomes chr, for associated traits for tolerance to salinity in the F
5
–derived
recombinant inbred lines from IR29×Hasawi
QTL
Chr
Peak marker
Position
(cM)
Flanking marker
Flanking marker
position (cM)
Additive
effect
Peak LOD R
2
(%)
z
Plant height
qPH1.1
1
id1024836*
162.6
id1023892
-
id1024836 158.1
-
163.5
2.116
4.657
13.8
qPH1.2
1
id1025983*
168.6
id1024972
-
id1025983 164.4
-
170.3
2.062
4.257
12.7
Dry weight
qDW1.1
1
id1014176*
102.6
id1012048
-
id1014176 90.7
-
102.9
0.203
11.342
30.4
qDW2.1
2
id2012453*
116.8
id2009319
-
id2012453 96.4
-
118.1
0.317
17.169
42.3
qDW2.2
2
id2014034*
130.8
id2014034
-
id2016108 129.6
-
144.5
0.315
16.851
41.7
qDW6.1
6
id6014475*
108.5
id6013529
-
id6014475 104.1
-
108.7
0.069
3.604
10.9
Fresh weight
qFW2.1
2
id2007526*
68.8
id2004774
-
id2007526 40.1
-
80.3
0.184
3.487
10.6
Note: * indicates lacking peak marker at a particular postion but named after nearest marker;
z
Percentage of total phenotypic variance
explained by a particular QTL
1.7 Plant
height
Both
QTLs
identified
for
plant
height
qPH1.1
and
qPH1.2
,
were
located
on
chromosome
1
(Table
6),
Their
contribution
to
the
phenotypic
variation
for
this
trait
was
13.8%
and
12.7%
respectively.
The
LOD
scores
were
4.66
and
4.26
for
qPH1.1
and
qPH1.2
.
Both
QTL
had
positive
additive
effects
for
plant
height,
indicating
the
contribution
of
Hasawi
alleles
for
this
trait
when
measured
under
saline
stress.
1.8 Shoot
fresh
weight
One
QTL
qF2.1
,
for
this
trait
was
located
on
chromosome
2
(Table
6). This QTL with
a LOD
score
of
3.5
accounted
for 10.6% of
its
phenotypic
variation.
This
QTL
had
also
positive
additive
effects
on
shoot
fresh
weight
under
saline
stress,
confirming
the
contribution
of
Hasawi
alleles
to
this
trait.
1.9 Shoot
dry
weight
The
four QTL
for
shoot
dry weights
qDW1.1,
qDW2.1,
qDW2.2
and
qDW6.1
, were
on
chromosomes
1,
2
and
6.
The
contribution
of
the
phenotypic
variation
explained
by
each QTL
ranged
from
10.6%
to
42.3%
and
their
LOD
scores
varied
between
3.6
and
17.17
(Table
6),
The
additive
effects
of
the
four
QTL
were
positive
suggesting
that
Hasawi
alleles
enhanced
this
trait
under
saline
stress.
2 Discussion
2.1 Effect
of
salinity
on
Agronomic
traits
Rice
crop
is most
sensitive
to
salt
stress
at
the
early
seedling
stage
(1~3 weeks)
of
crop
development with
a
threshold
as
low
as
an
EC
of
3
dSm
−1
(Maas
and
Hoffmann,
1977; Khatun
and
Flowers,
1995,
Lutts
et
al.,
1995; Makihara
et
al.,
1999;
Singh
et
al.,
2004;
Shereen
et
al.,
2005).
In
our
experiments,
the
300
F
5:6
RILs
and
their
parents
(IR29
and
Hasawi)
were
evaluated
at
a
high
salinity
level
(EC=12
dSm
−1
). This
concentration
assisted
testing
whether
the
RILs
can
grow
under
high
saline
stress.
Salt
stress
resulted
in
a
substantial
decrease
in
fresh
weight
by
56%
across
the
RIL
genotypes;
all
the
measured
traits
were
also
considerably
reduced
by
salinity
such
as
seedling
height
(16%),
root
length
(20%)
and
dry weight
(22%).
The
effects
of
salinity were
also
reflected
by
the
high
mean
SES
score
(Table
1).
The
tolerant
RILs
had
lower
SES
scores
(3.0
vs.
8.8),
good
plant
height
(44
cm
vs
7
cm),
higher
root
length
(18
cm
vs
3
cm),
and
higher
fresh weight
and
dry weight
(Table
1)
than
the
sensitive RILs
and with Hasawi
being
intermediate
for
majority
of
these
traits.
This
data
confirmed
the
phenotypic
differences
between
the
tolerant
and
sensitive
RILs
as
well
as
with
their
parental
line.
Similar
findings
about
the
existence
of
variability
in
salinity
tolerance
among
rice
varieties
at
early
seedling
stage
have
been
reported
(Reddy
and
Vaid,
1983; Mondal
et
al.,
1988).
In
all
31 RILs
representing
10%
had
tolerance
level
similar
or
better
than Hasawi
as
determined
by
their
SES
score
of
4
or
less.
Seedling
height
decreased
under
saline
conditions
causing
a
reduction
of
16%
compared
to
the
control
trials.
The
decrease
of
seedling
height was
due
to
the
application
of
salinity which
has
been
reported
earlier
(Zeng
and
Shannon,
2000a). Munns
and Tester
(2008)