How real are the biosafety concerns from commercialization of Bt - cotton

摘要

The plant varieties developed through conventional plant breeding have never been challenged by human and environmental biosafety concerns because the plant breeders basically worked within a well known domain around the primary gene pool. The insecticidal delta endotoxin producing gene used for developing Bt- transgenic cotton is of bacterial (Vacillus thuringiensis - a soil bacterium) origin and therefore doubts have been raised about the behaviour of this gene in an alien environment of the transgenic plant in terms of allergenicity and toxicity to human beings as well as its impact on environment. Extensive data generated in the past revealed that the Bt-genes currently in use are devoid of any allergic reaction as well as toxicity in a number of test animals including large mammals. As far as environmental risks are concerned. Bt-transgenics, if not properly handled, are expected to promote development of resistance in insects against Bt-toxin. In fact laboratory studies and Bt biopesticide application in fields have demonstrated the vulnerability of Bt-gene to insects so far as development of resistance is concerned. Resistance in insects through transgenic plants under field conditions has not been reported as yet but it is only a question of time. It is, therefore, prudent that Bt-transgenic plants must be provided an efficient integrated pest management umbrella for prolonging their effective life. The concern relating to the horizontal gene transfer is infact real because cotton inspite of being self-pollinated, show an average of about five per cent cross pollination. Fortunately, the diploid and the wild species of cotton grown in India do not hybridize with the tetraploid Gossypium hirsutum. However, pollen transfer from transgenic to non-transgenic cultivated tetraploids grown in the vicinity can not be prevented. Hence, it is important that critical experiments must be planned to study the impact of Bt gene flow on the non target insects. The concerns relating to the transfer of npt-II gene, a selectable marker gene imparting resistance to the antibiotic kanamycin, from transgenic plants to human pathogenic bacteria cannot be negated but recent studies have shown that such transfers are rare and occur with a frequency much lower than the expected spontaneous mutation frequencies and therefore, do not seem to be of much consequence. The economic returns accuring to the farmers from transgenic cultivars is an issue of much greater significance. Hence, the biosafety protocols developed in India besides giving weitage to human & animal health and environment are heavily tilted towards establishing agronomic superiority of a transgenic variety before it is released for commercial cultivation.