Development of Broad- Spectrum Insect Resistance in Crop Plants

Abstract

Insect pests are among one of the major factors limiting crop productivity destroying 20- 30% of the world 's food supply. Insects not only cause direct losses to agricultural produce but also act indirectly as vectors for various plant pathogens. Many different strategies are being employed for pest control including chemical pesticides, biological pesticides, integrated pest management etc. Arthropods pests have been controlled almost exclusively with chemical insecticides. However, the use of chemical insecticides has been under extensive pressure dlle to their adverse effects on the environment, food and beneficial organisms. This has necessitated the search for safer and more effective pest control strategies. Bacillus thuringiensis (Bt) has been successfully used as a bio-control agent against major insect pests for the last many decades. In addition to this, a number of Bf genes have been identified which are effective against different insect pests. The expression of wild type Bt genes in early 1990s showed that for optimum expression of bacterial genes in plants, they must be modified according to plant preferred codons in addition to many other factors, which enhance mRNA stability. To date, a large number of different crop plants have been developed expressing different BI genes. Recentl y, however, reports regarding the development of resistance against BI crops among insect pests have necessitated evolving strategies for delaying resistance against Bf crops. It has been suggested that deployment of two or more Bt genes can impart durable and long lasting resistance against insect pests. The current study is an endeavor to develop different constructs of Bacillus fhuringiensis synthetic crylAc gene under different plant expressible promoters (rbcS and 35S), with and without introns. Another objective of this study was to develop and characterize transgenic tobacco expressing the Bt cry 1 Ac fused with the funnel web spider's CDatracotoxin-Hvla (CD-ACTX-Hvla) gene. This study shows that some of the transgeni c tobacco plant lines expressing the crylAc-CD-ACTX-Hvla resulted in 100% mortality in armyworm, which is otherwise repolied to be resistant to cryl Ac.