Critics say that since the
improved varieties of Bt
cotton have proven ineffective
as the bollworm has gained
resistance, the answer can’t be
another resistant variety. How
do you respond to it?
There is nothing like resistant
or tolerant cultivars to PBW.
Whatever we have introduced
a new generation of bt gene in
local material, all are basically
susceptible. The only variation in
damage is because of duration of
different cotton germplasm. Most of
the best hybrids are long duration
of 180-190 days and are bound
to suffer. The best way in rainfed
cultivation is to recommend hybrids
or varieties of short duration of
130-140 days which escapes the
damage. Bt cotton is still effective
in controlling American bollworm,
Helicoverpa armigera and to a great
extend the spotted bollworm Earias
spp.
The pink bollworm, Pectinophora
gossypiella, has partly developed
resistance to Bt protein because of
mismanagement of refuge planting.
In some cases, the expression of
insecticidal protein in some Bt
cotton hybrids gets greatly reduced
after 120 days and this amount of
protein is insufficient to check the
damage. Infact the low levels
BIOVOICENEWS.COM
21