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Fig. 4.5.
Marker-assisted backcrossing strategy for pyramiding three large-effect QTLs for drought tolerance in rice.
FS- foreground selection, RS- recombinant selection, BS- background selection.
under normal irrigated conditions (IRRI, unpub-
lished). Because of this initial success, pyramid-
ing of three large-effect QTLs (
qDTY
1.1
,
qDTY
2.1
and
qDTY
3.1
) in the popular variety Swarna,
and pyramiding
qDTY
1.1
,
qDTY
1.2
,
qDTY
2.2
, and
qDTY
12.1
in IR64 is under way. Lines with a QTL
from the original mapping population are inter-
crossed to bring the QTLs together, followed by
a series of backcrosses to recover the recipient
parent background (Figure 4.5). Foreground and
background selections are made in each genera-
tion of the backcross program. A large F
1
pop-
ulation is developed in each backcross genera-
tion, which also provides an opportunity to self
and test the effect of QTLs and to identify any
possible undesirable effects in early backcross
generations.
ping season uneven rainfall patterns can cause
flash floods, while in another stage of growth,
crops can be affected by drought. These occur-
rences not only lead to direct yield losses but
also increase the incidence of insects and dis-
ease. For example, the incidence of rice blast
is seen to increase with drought. It therefore
becomes important that genes/QTLs conferring
tolerance for a wide range of biotic and abi-
otic stresses be combined with drought-tolerant
QTLs. Efforts are now being made to combine
qDTY
1.1
,
qDTY
2.1
, and
qDTY
3.1
with
SUB1
in the
popular variety Swarna and in
qDTY
1.1
,
qDTY
1.2
,
qDTY
2.2
, and
qDTY
12.1
in IR64. Similarly, efforts
are being made to combine these QTLs with
genes such as
Bph20
and
Bph21
for brown
planthopper;
xa5, Xa13,
and
Xa21
for bacterial
leaf blight; and
Pi1
and
Pi2
for blast tolerance
(Figure 4.6).
CombiningDroughtQTLswithQTLsAffecting
OtherBiotic/AbioticStresses
Marker-AssistedRecurrentSelectionand
Genome-WideSelection
Recent trends in climate change have increased
the possibility of biotic and abiotic stresses in
rice-growing areas (Wassmann et al. 2009). It
is commonly observed that during the crop-
Molecular markers have been used in breeding
programs by means of identifying markers that
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