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Bt Research 2013, Vol.4 No.5 24-28
ISSN 1925-1939
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28
terms of seed cotton yield (kg/ha), mean boll weight
(g), bolls number per plant, Harvest index and seed
cotton yield of plants was determined as yield in upper
half and lower half of the plant since the purpose of
this evaluation was to understand reasons for the
genotypic differences in potentiality of these Bt
hybrids and know it
’
s implications in plant breeding ,
the identity of these hybrids is not disclosed and
instead they are represented by code numbers (Table 1).
3 Conclusion
Often non Bt hybrid genotypes are selected based on
potentiality and the parents are subjectedto transfer of
Bt gene through back cross breeding. It is very
important to know whether the genotype chosen for Bt
gene has ability to withstand the additional
reproductive load (sink). If the enhanced sink is not
matched by the source (mismatch between source and
sink ) this is reflected in the form of faster senescence
reduced boll load especially in the upper half of the
plant. These genotypes which lack matching
photosynthetic potential (source) wither under the
pressure of enhanced sink. This impact is often
noticed in the latter half of the growth. As a result, the
harvest index and seed cotton yield are reduced in
upper half of the plant. Some hybrids of non
–
Bt era,
which on developing Bt version are clearly showing
weaker upper half since they cannot cope with this
drain. The symptoms of weakened leaves, more prone
to reddening, disease incidence and senescence are
noticed commonly. This is leading to reduced boll
load and lower harvest index in the upper half as
compared to lower half.
References
Edge J.M., J. Benedict J.H., Carroll J.P., and Reding H.K.,
2001, Bollgard cotton: an assessment of global economic,
environmental, and social benefits, J. Cotton Sci.,
5
:
121-136
Patil S.S., 2010, Priorities of conventional breeding in the era of
Bt
cottons, In: Proc. National Symposium on
Bt
cotton:
Opportunities and prospects., pp.46-52
Purcell J., and Perlak F., 2004, Global impact of insect– resistant
Bt
cotton, Ag. Bio. Forum,
7
(1-2): 27-30