The Hindu Business Line : Bt factor, a reason for higher cotton output

Flush factor
The toxin levels in Bt cotton peak at around 75 days and remain at those levels till 100-110 days.
The larvae feeding on the bolls thus cannot survive and the farmer is able to harvest the entire six quintals.

Harish Damodaran

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New Delhi, Feb. 18 Between 2002-03 and 2007-08, the country’s cotton production has shot up from 136 lakh bales (of 170 kgs each) to an estimated 310 lakh bales. While some of this may be due to a near-quarter jump in area sown (from 76.67 lakh hectares to 95.3 lakh hectares), more significant though is the contribution of yields, which have gone up from 302 kg to 553 kg (lint) per hectare.

50% relates to Bt

But how much of the higher yields have been a result of Bt cotton, which coincidentally was introduced in 2002 and covered 62 lakh hectares or almost two-thirds of the total cotton area in 2007? According to Dr C.D. Mayee, Chairman of the Agricultural Scientists Recruitment Board (ASRB), “There is no doubt that at least 50 per cent of the yield increase is attributable to Bt technology”.

In the rain-fed belt of central India, cotton is normally sown just after the onset of monsoon around June 20. Once sown, the crop starts bearing flowers in 40 days and after 65 days (when 50 per cent of flowering is over), the setting of the bolls (the pods containing the seeds from which the cotton fibres grow) happen.

Three flushes

The bolls (and the fibres inside) then grow till they mature and fully form by about 110 days. Once the boll formation takes place, it takes another 10-15 days for the bolls to burst and the exposed dried fibre to be ready for the “first-flush” picking. In the meantime, the plants below also flower, pollinate and form bolls, leading to subsequent ‘flushes’ every 20-30 days.

“For a typical 170-180 day crop, you have three flushes, with a total yield of 10 quintals an acre. Of this 10, six quintals can theoretically come from the first flush, three from the second and one from the third,” Dr Mayee noted.

But the “theoretical” six quintals in the first flush is not always realised. “The problem is in the 65 to 110 days period, when temperatures are in 35-36 degree Celsius range, humidity levels touch 90 per cent and there is cloudy weather with occasional rains. This environment is highly conducive for infestation by the American bollworm larvae, which feed into the bolls. So, the farmer, instead of six quintals, ends up getting only 1-2 quintals from the first flush. While the weather may cool down later and there may be no bollworm attacks in the next two flushes, they cannot, however, compensate for the yield loss from the first flush picking,” he pointed out.

Bt cotton’s effectiveness stems from the Bacillus thuringiensis gene, which is incorporated into the parent hybrid or variety.

This foreign gene, isolated from a soil bacterium, synthesises proteins that are toxic to the American bollworm.

Toxins & larvae

“As the cotton plant grows, it simultaneously produces these toxins. The toxin levels peak at around 75 days and remain at those levels till 100-110 days. The larvae feeding on the bolls, therefore, cannot survive and the farmer is able to harvest the entire six quintals from the first flush,” Dr Mayee added.

He claimed that the higher yields being reported on the fields are mostly on account of more productive first-flush pickings, courtesy Bt cotton.

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