Agronomic Efficiency of Herbicide Tolerant Crops in Peninsular India—A Review

Abstract

Crops made resistant to herbicides by biotechnology are being widely adopted in various parts of the world and several herbicide resistant crops have become available in many countries for commercial cultivation. But in India, the technology of herbicide tolerant crops is in initial stage of field evaluation. Hence, field trials have been carried out to evaluate and consolidate the agronomic advantages of herbicide tolerant transgenic cotton and maize. Herbicide tolerant stacked traits of maize and cotton have been evaluated under Bio-safety Research Level (BRL I) as confined field trials for its agronomic efficiency on weed control and enhanced crop productivity at Tamil Nadu Agricultural University (TNAU), Coimbatore and Punjab Agricultural University (PAU), Ldhiana for many years. In both crops, potassium salt formulation of glyphosate was sprayed at different doses (900, 1,350, 1,800, 2,700, 3,600 and 5,400 g a.e./ha twice at 25 days after sowing (DAS) and 60 DAS in cotton and 900, 1,800 and 3,600 g a.e./ha at 25 DAS in maize). Evaluation was made on weed control efficiency, phyto-toxicity on crops, yield and economics and carry over effects on the succeeding crops. Application of glyphosate at 2,700 g a.e./ha recorded lower weed density, dry weight and higher weed control efficiency (WCE) in cotton. Post-emergence (POE) glyphosate at 900, 1,800 and 3,600 g a.e./ha registered lower weed density, dry weight and higher WCE in transgenic Hishell and 900 M Gold and in 30V92 and 30B11 corn hybrids. Post-emergence application of glyphosate in transgenic maize hybrids did not affect the germination percent, vigour and yield of succeeding green gram in the transgenic maize trials and sunflower, soybean and pearl millet in cotton trials. Phytotoxicity symptoms were not observed in cotton with glyphosate at lower doses viz., 900, 1,350, 1,800 and 2,700 g a.e./ha. Higher doses viz. 3,600 g a.e./ha and 5,400 g a.e./ha were noticed with phytotoxicity symptoms at early stages of herbicide application. Glyphosate applied at 900, 1,350, 1,800 and 2,700 g a.e./ha recorded more number of bacteria, fungi and actinomycetes compared to atrazine treatments. Higher grain yield was recorded with POE application of glyphosate at 900, 1,800 and 3,600 g a.e./ha in Hishell and 900 M Gold transgenic hybrids and higher net return and benefit cost ratio were recorded in glyphosate at 1,800 g a.e./ha in transgenic 900 M Gold in all the four seasons. Post-emergence application of glyphosate at 900 g a.e./ha and 1,800 g a.e./ha registered higher grain yield in transgenic 30V92 and 30B11 corn hybrids. In maize and cotton transgenic crops, post-emergence weed management with glyphosate proved to be the better management option for the control of weeds.