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Cotton Genomics and Genetics
67
heterosis over commercial check MRC 6918 and the
cross ZCH 8 X (DB 533 x DB 534 F
4
IPS 33) (-89.07)
exhibited lowest significant negative heterosis over
MRC 6918. Thirty nine crosses showed significant
heterosis in negative direction and only one cross
showed significant heterosis in positive direction over
MRC 6918. In case of DCH 32 check, the cross ZCH
8 X (DB 533 x DB 534 F
4
IPS 52) (41.83) showed
highest significant positive heterosis over this check,
but the cross ZCH 8 X (DB 533 x DB 534 F
4
IPS 33)
(-86.97) recorded lowest significant negative heterosis
value over DCH 32 commercial check. Thirty crosses
exhibited significant positive heterosis over DCH 32
commercial check and eighteen crosses showed
significant negative heterosis.
1.5 Stomatal conductance (µmol·m
-2
·s
-1
)
The rate of stomatal conductance, or its inverse,
stomatal resistance, is directly related to the boundary
layer resistance of the leaf and the absolute
concentration gradient of water vapor from the leaf to
the atmosphere. Stomatal conductance values ranged
from 2.38 [DB 533 x DB 534 F
5
IPS 55] to 0.55 [DB
533 x DB 534 F
5
IPS 15] among males/ lines, 1.22
[178-24] to 0.78 [DH18-31] among females/testers
and 1.17 [ZCH 8 X (DB 533 x DB 534 F
4
IPS 52)] to
0.09 [178-24 X (DB 533 x DB 534 F
4
IPS 15)] among
derived F
1
crosses.
Per cent heterosis of F
1
crosses over their respective
mid parental values ranged from 75.94 [ZCH 8 X (DB
533 x DB 534 F
4
IPS 52)] to -90.67 [178-24 X (DB
533 x DB 534 F
4
IPS 15)]. Sixty three crosses showed
significant negative heterosis and eleven crosses
showed significant positive heterosis over their mid
parent. The cross ZCH 8 X (DB 533 x DB 534 F
4
IPS
52) (53.95) recorded highest significant positive
heterosis over commercial check MRC 6918 and the
cross 178-24 X (DB 533 x DB 534 F
4
IPS 15) (-88.16)
exhibited lowest significant negative heterosis over
MRC 6918. Thirty eight crosses showed significant
heterosis in negative direction and nine crosses
showed significant heterosis in positive direction over
MRC 6918. In case of DCH 32 check, the cross ZCH
8 X (DB 533 x DB 534 F
4
IPS 52) (234.29) showed
highest significant positive heterosis over this check,
but the cross 178-24 X (DB 533 x DB 534 F
4
IPS 15)
(-74.29) recorded lowest significant negative heterosis
value over DCH 32 commercial check. Seventy four
crosses exhibited significant positive heterosis over
DCH 32 commercial check and six crosses showed
significant negative heterosis. The majority of crosses
showing significant negative heterosis over mid parent
and MRC 6918 for stomatal conductance, while
showed significant positive heterosis over DCH 32
check. Gopinath and Madalageri (1985) reported
heterosis for stomatal conductance over mid-parent
values. Majority of hybrids possessed higher stomatal
conductance as compared to parents. This may be
attributed to higher stomatal frequency, length and
breadth of stomata observed in hybrids. Austin (1977)
and Jing and Ma (1990) reported that reduced
stomatal
frequency would reduce stomatal
conductance and increase the yield due to increased
water use efficiency under water limiting conditions.
1.6 Transpiration rate (mmol H
2
O m
-2
·s
-1
)
The leaf transpiration and stomatal resistance are
directly related to number of stomatal present per unit
leaf area (Vande Roovart and Fuller, 1935).
Transpiration rate values ranged from 16.66 [DB 533
x DB 534 F
5
IPS 105] to 7.92 [DB 533 x DB 534 F
5
IPS 14] among males/ lines, 11.77 [178-24] to 10.09
[DH 98-27] among females/testers and 10.04 [DH
98-27 X (DB 533 x DB 534 F
4
IPS 1)] to 2.07 [178-24
X (DB 533 x DB 534 F
4
IPS 32)] among derived F
1
crosses.
Per cent heterosis of F1s over their respective mid
parent values ranged from -5.85 [178-24 X (DB 533 x
DB 534 F
4
IPS 38)] to -79.10 [178-24 X (DB 533 x
DB 534 F
4
IPS 32)]. Ninety seven crosses showed
significant negative heterosis over their mid parent.
The cross DH 98-27 X (DB 533 x DB 534 F
4
IPS 1)
(55.26) recorded highest significant positive heterosis
over commercial check MRC 6918 and the cross
178-24 X (DB 533 x DB 534 F
4
IPS 32) (-67.93)
exhibited lowest significant negative heterosis over
MRC 6918. Thirteen crosses showed significant
heterosis in negative direction and only one cross
showed significant heterosis in positive direction over
MRC 6918
Bt
check. In case of DCH 32 check, the
cross DH 98-27 X (DB 533 x DB 534 F
4
IPS 1) (93.92)
showed highest significant positive heterosis over this
check, but the cross 178-24 X (DB 533 x DB 534 F
4
IPS 32) (-59.94) recorded lowest significant negative
heterosis value over DCH 32 commercial check. Two
crosses exhibited significant negative heterosis over
Cotton Genomics and Genetics