Cotton

Bt. COTTON

The Bacillus thuringiensis research began when the Japanese bacteriologist, Ishiwata isolated the bacillus for the first time in 1901. A decade later, Ernest Berliner isolated a similar organism from diseased granary populations of Mediterranean flour moth larvae obtained from Thueringen city in Germany and named the bacterium Bacillus thuringiensis (Bt.). The advancement in genetic engineering and molecular biology in the early eighties made the cloning of Bt. Crystal protein (cry) gene essay for the first time in 1981. Since then, more than 100 cry genes have been successfully cloned and added to the growing list. Today, the most efficient way to deliver cry genes seems to be the development of transgenic plants expressing them.

Mode of action of Cry protein

The Cry protein when ingested by the insect, is first converted from the inactive form to active toxin protein by proteolysis in the alkaline mid gut region, which then binds to specific receptors present on the midgut. When the activated toxin binds to receptors, the interaction generates pores on mid gut membrane. The formation of pore leads to gut paralysis and finally death of the larvae. The toxins are most effective on the newly hatched larvae (1 instar) compared to other stages of the insect.

Bt. Cotton

The first version of Bt. Cotton (BollguardTM, Monsanto) containing cry1Ac gene was released in USA during 1996. Ingard ® is the popular Bt. Cotton variety in Australia grown in 30,000 ha during 1997-98. Commercial release of Bt. Cotton in India was approved very recently (March in 2002). The Ministry of Environment and Forests (MoEF), Government of India (GOI), approved the release into the environment and commercialization, of three transgenic Bt. Hybrid cotton varieties, developed by Mahyco., namely Bt. MECH 12, Bt. MECH 162 and Bt. MECH 184, containing Cry 1ac gene from Bacillus thuringiensis, and the approval is valid for three years from April 2002.

Benefits of Bt. Cotton

Reduction in pesticide use

The bollworm complex is a major cotton pest, causing serious damage to floral structures of the cotton plant and requires extensive treatment with chemical insecticides in conventional cotton. The effectiveness of Bt. Cotton has resulted in a dramatic reduction in the use of chemical insecticides.

Economic benefits

Bt. Cotton is a tool that provides growers with an economical approach to manage, cotton bollworms, but it does not address all insect pest management issues. As cotton yield potential increases, due to various management and satisfactory environmental factors, the value of the protection provided by Bt. Cotton increases. Secondly, the greater the target pest infestation level, the more money is saved on insect control costs compared to conventional cotton managed with conventional insecticide programs. Insect management programs for conventional cotton often require additional monitoring and insecticide applications under high pest – infestation levels, whereas these applications are not in Bt. Fields.

Key points to be considered

• Bt. Cotton hybrids generally show higher retention of first formed bolls due to low fruiting point and boll damage.
• Due to early retention of bolls in Bt. Hybrids the boll bursting commenced nearly 15-20 days in advance and required less number of pickings to complete the harvest.
• In Bt. Cotton hybrids ETL (one larvae/plant) for bollworm population crossed only once that too after 90 days.
• Population of bollworm especially Helocoverpa was significantly lesser in number in Bt. Cotton.
• Bt.Cotton required one or two pesticide sprays thus fitting well in IPM module. The saving in plant protection cost was Rs. 1500 per ha besides an additional return by way of higher yield to the tune of Rs. 7000 – 8000 per ha.

(Source: AICCIP annual report 2001-02).

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