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Bt Research 2013, Vol.4 No.5 24-28
ISSN 1925-1939
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1.2 The impact of enhanced sink
With same photosynthetic output (source) the quantum
of sink has increased. Some genotypes lack matching
photosynthetic potential (source) to meet extra
demand of sink and they cannot cope with this drain.
Leaves are weakened, subsequent reddening, disease
incidence and senescence (Figure 2). In some hybrids
there is Mismatch between source and sink at a later
stage of growth (upper half of the plant). By going to
the table number 2 we can see the physiological
changes in cotton through introduction the Bt gene.
1.3 Overcoming the demand of enhanced sink
induced due to Bt gene
There are two ways to overcome the demand of
enhanced sink induced due to Bt gene.
1.3.1 Genetic intervention enhancing source to
meet the demand of enhanced sink
Those Bt genotypes with enhanced photosynthetic
ability (extra source) can match the demand of
“
enhanced sink (Bt gene induced)
”
.Such of the
genotypes reveal higher foliage, higher boll load in
lower as well as upper halves and almost same harvest
index values in both the halves. Stay green types
known for green foliage even when bolls are open are
likely to be more responsive to integration of Bt gene
(Figure 3).
The breeder should have an insight into an ideal plant
type which can maximize productivity based on
optimum blending type which can maximize
productivity based on optimum blending of desirable
traits seen in different plant types. The robust plant
type (tall growing) occupies a larger three- dimensional
space but reveals a poor packing of bolls. In contrast
with this a compact plant type occupies a smaller
three- dimensional space but reveals better packing of
bolls. It is possible to get robust and compact types,
which are equally potential but it will be an ideal plant
type that blends the desirable features seen in robust
and compact plant types. Such ideal intermediate
types may require a closer spacing and can maximize
productivity per unit area. The features of ideal plant
types again vary depending on the situation say like
irrigated rainfed, machine picking, etc.
1.3.2 Chemical intervention (Ethrel spray)
Ethylene spray is expected to induce initial square
dropping causing additional vegetative growth making
the plant competent to bear enhanced sink (Figure 4).
2 Materials and Methods
The experimental material used in the present study
comprised of fifteen Bt cotton hybrids representing
differences in Bt sources were evaluated at Dharwad,
Karnataka (India) with two replication was laid out in
Randomized Complete Block Design (RCBD) during
2009-2010. Each entry was sown in 2 row plots of 6
m length spaced at 90 cm with recommended dose of
fertilizer and treatment of seeds with Imidochloprid,
2-3 seeds were dibbled per spot in each row and
thinning was attended to retain one healthy plant per
hill at 25 days after sowing. All the recommended
package of practices were followed to rise healthy
crop. Productivity of the hybrids was assessed in