HERBICIDE TOLERANT CROPS
Ever since Man domesticated crops, he has been struggling with weed menace. Unless the weeds are removed the crop will not grow properly, obtain nourishment from the soil and produce good yield. The good old practice of manual weeding has become labour-intensive, expensive and in recent times highly uneconomical because of the shortage of manual labour.
Several weedicides such as Glyphosate, Sulfonyl Ureas, Phosphinothricin and atrazine-type herbicides have been in use in agriculture for the past five decades but their use is limited because the crop plant are also susceptible to weedicides.
Development of Herbicide Tolerant (HT) Crops:
Initially one needs to identify herbicides that kill all plants but not be toxic to human beings, animals or bacteria or to the environment. The crop plant is then engineered to be resistant to the herbicide. Resistance achieved by introducing genes that detoxify the herbicide or genes that encode mutant forms of the protein/enzyme that are not affected by the herbicide. Approach has benefits because it makes the herbicides more effective and thus reducing the amount that need to be used
Cultivation of herbicide tolerant crops has several advantages in harmony with the philosophy of sustainable agriculture. Herbicides used with most HT crops tend to be less toxic and persistent than the herbicides they replace, while HT varieties can complement the use of no-till systems that reduce soil erosion and fossil fuel emissions. Thus, benefits of HR crops are multi-faceted.
- Facilitates adoption of reduced tillage systems (strip-till)
- Sustainable agricultural systems by maintaining natural resources
- Enhanced nutrient availability
- Convenience and coverage of large areas
- Timing of applications extended
- Allows replanting of crops (e.g., soybean) if stand is poor
Better weed control:
- Less crop damage
- Improved yields
- More consistent weed control
- Tough grasses and perennials
Globally commercialized HT crops:
Several HT crops are cultivated around the world today. These are Canola, Soybean, cotton, Carnation, Chicory, corn, sunflower, tobacco and Sugar beet. These crops occupy 62% of the total area of 160 mHa GM crops in 2011 in more than twenty countries.
HT Crops are totally safe:
The weedicides used in conjunction with HT crops are safe, degradable and benign to soil flora and fauna. The genes encoding herbicide-detoxifying enzymes (EPSPS, PAT etc) are sourced from bacteria that commonly occur in soils. Some of these enzymes such as EPSPS exist in plant species too. Enormous literature exists on the safety of HT crops (Lemaux, 2009). The history of safe use of HT crops for the past 16 years is a testimony to the safety and efficacy of these crops.
Regulatory agencies in several countries have concluded that HT crops do not pose any environmental and health risks as compared to their non-GM counterparts. Foreign proteins were assessed for potential toxic and allergenic activity in accordance with international guidelines. These proteins/enzymes are from sources with no history of allergenicity or toxicity.
A major environmental concern associated with herbicide-tolerant crops is their potential to create new weeds through out-crossing with wild relatives or simply by persisting in the wild themselves. This potential, however, is assessed prior to introduction and is also monitored after the crop is planted. The current scientific evidence indicates that, in the absence of herbicide applications, HT crops are no more likely to be invasive in agricultural fields or in natural habitats than their non-GM counterparts (Dale et al., 2002).
Dale, PJ, B Clarke, and EMG Fontes. 2002. Potential for the Environmental Impact of Transgenic Crops. Nature Biotechnology. 20: 567-574.
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Lemaux, P. 2008. Genetically Engineered Plants and Foods: A Scientist’s Analysis of the Issues (Part I). Annual Review of Plant Biology. 59:771–812
Lemaux, P. 2009. Genetically Engineered Plants and Foods: A Scientist’s Analysis of the Issues (Part II). Annual Review of Plant Biology. 60: 511-559.
Fernandez-Cornejo, J., Hendricks, C., & Mishra, A.K. (2005). Technology adoption and off-farm household income. Journal of Agricultural and Applied Economics, 37: 549-563.
Nap, J.P. (1999). A Transgene-centred Approach to the Biosafety Assessment of Transgenic Herbicide-tolerant Crops. Biotechnology and Development Monitor, 38: 6-11.
Duke, S.O. and Cerdeira, A.L. 2010. Transgenic Crops for Herbicide Resistance. In: Transgenic Crop Plants, Vol. 2: Utilization and Biosafety. C. Kole, C.H., Michler, A.G. Abbott and T.C. Hall, Eds., Springer-Verlag, Berlin/Heidelburg, PP. 133-166