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Heterosis Performance Seed Cotton Yield Physiological Parameters F
1
Inter Specific Hybrids Cotton
68
DCH 32 commercial check and seventeen crosses
showed significant positive heterosis.
2 Conclusion
In this part of the study nature and magnitude of
variability for combining ability was assessed against
four hirsutum tester included in the heterotic box.
The derived F
1
crosses (28 barbadense lines x 4
hirsutum testers) were compared with the bench mark
crosses (two barbadense lines x 4 hirsutum testers) of
the heterotic box, best Bt check hybrid (MRC 6918)
and non
Bt
check (DCH 32). Many derived F
1
crosses
were found to be more productive than non
Bt
check
DCH 32 (48 hybrids) and the
Bt
check MRC 6918 (35
hybrids). The potential crosses like DH 98-27 X (DB
533 x DB 534 F
4
IPS 49), DH 98-27 X (DB 534 x DB
533 F
4
IPS 22) and DH 98-27 X (DB 533 x DB 534 F
4
IPS 52) recorded highest per se performance for seed
cotton yield. These potential crosses recorded highly
significant heterosis over mid parent for seed cotton
yield. They also recorded significant heterosis for
other physiological parameters.
Apart from showing high productivity the potential
cross DH 98-27 X (DB 533 x DB 534 F
4
IPS 49
showed higher value of photosynthetic rate and
stomatal conductance. This potential cross is example
for blending of yield characters and physiological
parameters.
3 Materials and Method
To create recombinational variability for combining
ability, the elite barbadense lines DB 533 and DB 534
were crossed during 2007~2008. During two seasons
2008~2009 and 2009~2010 these barbadense crosses
were advanced to F
2
and F
3
generations, respectively.
The F
3
lines were evaluated for productivity and fiber
quality parameters realizing the emphasis laid on
developing ELS (Extra Long Stable) cotton hybrids
out of 171 F
3
lines, only those F
3
lines with acceptable
fiber strength were utilized in the study on
recombinational variability of combining ability.
During 2010~2011 those twenty eight F
4
lines of
barbadense cross DB 533 × DB 534 depending on the
higher value of fiber tenacity, were crossed with the
selected four hirsutum testers viz., DH 98-27 (T
1
),
ZCH 8 (T
2
), 178-24 (T
3
) and DH 18-31 (T
4
) selected
based on earlier study. Each barbadense F
4
line was
involved in a set of crosses (112 crosses refer to as
derived F
1
crosses) were subjected to Line x Tester
analysis.
The physiological observations have taken by using
portable photosynthesis system of Infra Red Gas
Analyzer (IRGA), which measures gas exchange
parameters apart from environmental parameters
There are several methods of measuring CO
2
fixation
or exchange in plants but, the modern techniques of
determining CO
2
fixation using infra red gas analysis
(IRGA) of CO
2
is most widely employed owing to the
precision of detecting very small changes in CO
2
concentrations. This method is very sensitive for CO
2
uptake by small leaves or even segments of leaves.
The IRGA records the change in CO
2
concentration in
the system and the rate of change with time gives an
estimate of the CO
2
or water exchange rate. The main
advantage of this method is that it can be used at a
wide range of CO
2
concentrations, light, relative
humidity and temperature and for studying the effects
of these environmental factors that parameters
influencing photosynthesis or gas exchange parameters.
3.1 Photosynthetic rate (µmol CO
2
m
-2
·s
-1
)
Photosynthesis, the conversion of light energy to
chemical energy and the utilization of the chemical
energy. The rate of photosynthesis is affected by a
number of factors including light levels, temperature,
availability of water, and availability of nutrients. If
the conditions that the plant needs are improved the
rate of photosynthesis increases.
3.2 Stomatal conductance (µmol·m
-2
·s
-1
)
Stomatal conductance, measured in µmol m
-2
s
-1
is the
measure of the rate of passage of carbon dioxide CO
2
entering, or water vapor exiting through the stomata of
a leaf. Stomata are small pores on the top and bottom
of a leaf that are responsible for taking in and
expelling CO
2
and moisture from and to the outside air.
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.
3.3 Transpiration rate (mmol H
2
O m
-2
·s
-1
)
Loss of water in the form of water vapour from the
internal living tissue of the leaf through the aerial
parts such as leaf, green stem, etc., under the influence
of sunlight is called as transpiration. The excess
Cotton Genomics and Genetics