Growing Refugia Crop to Maintain Bt Cotton Resistance: A Necessity

Cotton (Gossypium hirsutum) is an important fibre crop. As per recent 2nd advance estimates given by Department of Agriculture, Cooperation and Farmer’s Welfare (Govt. of India), the estimated production for the year 2019-2020 is 34.89 million cotton bales (of 170 kgs each). The three cotton bollworms viz., Helicoverpa armigera, Pectinophora gossypiella and Earias vitella being internal feeders are difficult to control and feeds on fruiting parts of crop, which can cause yield losses of up to 80% in cotton. Farmers are using large amount of insecticides for saving the crop from attack of this destructive pest (bollworm), which increases the cost of production and also pollutes natural resources like soil and water. 

In 2002, transgenic Bt was introduced in India to reduce crop damage by bollworm infestation which is developed by incorporation of insecticidal genes from Bacillus thuringiensis like Cry1Ac, Cry2Ab etc., which provides resistance against bollworms and also reduces pesticidal cost besides increasing productivity. Upon feeding by insects on Bt plant, the Bt crystal toxin, binds to specific receptors in the epithelial cells of the larval midgut which  disrupts the potassium pump and results in pore formation in the plasma membrane of columnar cells which leads to an osmotic imbalance and subsequently causes death of the insect. However, in the recent past, it has been observed that Bt cotton is getting affected by bollworm which is a typical case of Bt resistance breakdown as resistance has been acquired by bollworms against toxic Cry proteins that enables them to survive on Bt cotton. The self-mated progenies of this resistant insect lead to further generations of resistant insect population. It is therefore necessary to plant of 20% refugia crop (non-Bt cotton) around the Bt cotton for maintenance of Bt-cotton resistance against bollworm as prescribed by- ‘The Genetic Engineering Appraisal Committee (GEAC), Govt. of India’ and the design of refugia that can be followed in Bt cotton is depicted in Figure given below.

If there are susceptible insects in the fields, resistant bollworm can randomly mate with the susceptible ones and because as resistance is a recessive trait, progeny developed from the mating of susceptible bollworm and resistant bollworm becomes susceptible to Bt cotton. The probability of the susceptible insects from refugia plants mating with the resistant insects from Bt plants would be high owing to presence of large population of susceptible insects from the non-Bt refuge. Thus, growing a refuge crop, in close proximity helps in maintaining the effectiveness of Bt protein. Recently pigeonpea, has also been approved as refugia crop to be cultivated as border rows around Bt cotton. 

Conclusion  

Growing of refugia/non-Bt cotton in about 20% of Bt cotton cultivated area is necessary for avoiding the outbreaks of bollworms resistance to Bt cotton. Insecticidal sprays on refugia crop should be avoided because the purpose of planting refugia crop is to maintain susceptible bollworm population.  

References: 

http://agricoop.gov.in/ 

http://www.cicr.org.in/ 

Author

Simranpreet Singh Bola 

Ph.D. research scholar, Department of Agronomy, Punjab Agricultural University,  Ludhiana, Punjab, India. 

Email: ssaini447@gmail.com