Bt cotton (Bollgard-II)

Bollgard-II (BG-II) is a transgenic cotton trait expressing two insecticidal proteins, Cry1Ac and Cry2Ab, derived from the soil bacterium Bacillus thuringiensis. The stacked event was developed by Mahyco-Monsanto Biotech as a successor to the single-gene Bollgard-I (BG-I) and is the dominant Bt trait in Indian commercial cotton hybrids.

Composition and mode of action

The two Cry proteins are expressed constitutively in cotton tissue and bind to specific receptors in the midgut of lepidopteran larvae, causing pore formation, gut paralysis and death. The stacking of Cry1Ac with Cry2Ab provides two complementary modes of action intended to delay the evolution of insect resistance.

Target pests

BG-II is directed at the lepidopteran bollworm complex of cotton, principally American bollworm (Helicoverpa armigera), spotted bollworm, Pink Bollworm, and Spodoptera. It does not control the sap-sucking pest complex (see Sucking Pest Complex Cotton, Jassid Leafhopper Cotton, Whitefly In Cotton Chilli) or non-lepidopteran pests, which still require conventional insecticide programmes.

Regulatory status in India

BG-I received Genetic Engineering Appraisal Committee (GEAC) approval for commercial cultivation in 2002, and BG-II was approved in mid-2006. These remain the only two transgenic cotton events cleared in India; no new GM cotton event has been approved since 2006. Herbicide-tolerant stacks such as Roundup Ready Flex remain unapproved (see Roundup Ready Cotton Regulatory).

Resistance and management

Indian field populations of pink bollworm developed resistance to Cry1Ac around 2009 and to the Cry1Ac+Cry2Ab stack around 2014-15, eroding BG-II's protection against this pest. Insect-resistance-management strategies including structured refuge and later refuge-in-bag (Refuge In Bag Cotton) were mandated to delay resistance.

References

Approval Process and Adoption of Bollgard Cotton in India. CABI Digital Library.
Bollgard I and Bollgard II technologies. Testbook reference.