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yield per se under field conditions. It is there-
fore very important that the identified QTL be
robust enough to show an effect under a vari-
ety of environmental conditions as well as under
varying drought intensities. One way to over-
come this challenge could be to screen the map-
ping population for high grain yield in the target
environment under naturally occurring drought
stress and to use these data for QTL identi-
fication. However, performing such large-scale
experiments in the target environment could be
expensive, and the chances of failure can be high
because of the chance of rainfall during the crit-
ical stress period. Another alternative could be
to identify QTLs under managed stress condi-
tions and test a random subset of the mapping
population under naturally occurring drought
in multi-location trials. This strategy enables
widespread testing of the QTL under varying
environmental conditions and water regimes.
Bernier and colleagues (2009) tested a random
set of RILs in 21 experiments conducted at IRRI
and in eastern India. These experiments con-
firmed the effect of
qDTY
12.1
under varied situa-
tions and further showed that the relative effect
of the QTL increased with increasing severity of
stress. Under well-watered conditions,
qDTY
12.1
showed no effect but in the most severe stress
treatments, it showed an additive effect of more
than 40% of the mean trial yield. The second
important aspect of drought-yield QTLs has been
their effect across elite genetic backgrounds.
Among a large number of QTLs identified for
drought tolerance in rice, only a few could show
their effect across genetic backgrounds. Geno-
typing strategies such as BSA also make it pos-
sible to screen a large number of mapping pop-
ulations simultaneously for the presence of a
QTL affecting grain yield in more than one
background. The QTL
qDTY
1.1
- contributed by
the donor N22 and functional across the back-
grounds of the mega-varieties MTU1010, IR64,
and Swarna (Vikram et al. 2011) - was identi-
fied using BSA for two of the three populations,
while WGS was carried out for the third popu-
lation. Swamy and colleagues (2011) identified
14 meta-QTLs among 53 yield QTLs reported
in 15 studies. This study also tested a panel of
random drought-tolerant donors for the identi-
fied drought yield QTLs and reported the pres-
ence of
qDTY
12.1
in 85% of the lines, followed
by
qDTY
4.1
in 79%, and
qDTY
1.1
in 64% of the
lines.
Effect of Drought Yield QTLs on
Multiple Yield-Related Traits under
Drought
It is interesting to see that, within or near the
regions showing an effect on grain yield under
drought, regions affecting plant height, biomass,
HI, and DTF under drought were also identi-
fied. In some cases, the same regions are likely
to show an effect on yield under drought and
DTF or plant height. This may be either a
result of a close linkage between regions affect-
ing two traits or a pleiotropic effect of the
QTLs for grain yield under drought on DTF
and plant height. For example,
qDTY
12.1
, a large-
effect QTL for grain yield under upland drought,
showed its effect on almost all traits, such as
DTF, plant height, biomass, HI, DRI, and pan-
icle number m
−
2
. Similarly,
qDTY
3.1
showed
an effect on DTF along with grain yield under
severe lowland drought (Venuprasad et al. 2009).
Another recently reported QTL,
qDTY
1.1
,
was
related to DTF, plant height, HI, and biomass
across N22/Swarna and N22/MTU1010 popu-
lations, and was related to DTF, plant height,
and biomass in N22/IR64 populations. Swamy
and colleagues (2011) compared the synteny of a
meta-QTL coinciding with this region with other
crops. It was observed that this region was syn-
tenic to a region on chromosome 3 in maize near
marker
msu2
, on chromosome 4B in wheat near
marker
Rht b1
, and in barley on chromosome
6H near marker
Bmac0316
. In the same study,
another meta-QTL coinciding with
qDTY
3.1
was
also found in maize on chromosome 1 near
marker
Umac107a
. The study also reported the
association of all these markers to grain yield
under drought in their respective crops (Swamy
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