a recent development may help farmers in India overcome the problem of pests attacking genetically modified (gm) cotton. Many farmers have started using insect-resistant gm bt cotton licensed by the us biotech giant Monsanto. The gm cotton carries the cry1ac gene of the bacterium Bacillus thuringiensis, which enables it to secrete a protein that is toxic to the pests. Now researchers from the Tamil Nadu Agricultural University in Coimbatore have cloned the cry2aa and cry2ab genes from indigenous isolates of a bacterium.

The work has been done by V Udayasuriyan, Shantanu Kumar, P Sangeetha and M Bharathi. The researchers isolated the cry2aa and cry2ab proteins from recombinant strains of the bacterium Escherichia coli that harbour cry2aa and cry2ab genes, and tested them for toxicity against a common pest, the cotton bollworm (Helicoverpa armigera) . The team found that cry2aa protein caused 100 per cent mortality of the bollworms at a concentration of 650 nanogrammes per millilitre after 48 hours. Cry2ab was not toxic to the insects (News India, June 2004).

The findings could help develop bt cotton strains using indigenous technology. But more importantly, it will help farmers in controlling the development of resistance in insects exposed to the cry1ac protein of Monsanto's cotton. bt cotton cultivars from Monsanto that express the cry1ac protein has been grown in India since 2002. "Continuous exposure of pests to a single kind of bt toxin can lead to the rapid development of resistance in insects,' warns Udayasuriyan. One way to prevent this is by