Glyphosate is a non-selective, broad-spectrum, systemic herbicide used for the control of weeds. Glyphosate resistant (GR) crops have been adopted on a massive scale by North and South American farmers. Currently, about 80% of the 120 million hectares of the global genetically-modified (GM) crops are GR crop varieties. However, the adoption of GR plants in China has not occurred at the same pace, owing to several factors including, among other things, labor markets and the residual effects of glyphosate in transgenic plants.

A team led by Prof. GUO Sandui and Prof. ZHANG Rui of Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, recently introduced the new herbicide-resistant cotton varieties having the ability for less accumulation of glyphosate residues.

GUO and colleagues demonstrated the co-expression of codon-optimized forms of GR79 EPSPS and N-acetyltransferase (GAT) genes in cotton. They found five-times more resistance to glyphosate with 10-fold reduction in glyphosate residues in two pGR79 EPSPS-pGAT co-expression cotton lines, GGCO2 and GGCO5. The GGCO2 line was used in a hybridization program to develop new GR cottons. Field trials at five locations during three growing seasons showed that pGR79-pGAT transgenic cotton lines have the same agronomic performance as conventional varieties, but were USD 390-495 cheaper to produce per hectare because of the high cost of conventional weed management practices. Thus, the strategy to pyramid these genes clearly worked, and thus offers attractive promise for the engineering and breeding of highly-resistant low-glyphosate-residue cotton varieties.

"The present study demonstrated that pyramiding of glyphosate resistance and detoxification genes conferred highly glyphosate-resistant plants that had low glyphosate-residue levels and did not suffer any yield losses. Although the exact biochemical mechanism has not been verified, it seems highly likely that the introduction of the detoxification GAT gene rapidly degraded significant amounts of glyphosate residues, resulting in more robust of glyphosate, thereby allowing the frequent use of glyphosate for weed control in farmer field." says Prof. GUO Sandui, the corresponding author of this paper.

"In the past decade, the planting area in China devoted to cotton production has dropped by around one third, due in part to sharp rises in labor costs. We anticipate that the introduction of pGR79 EPSPS-pGAT co-expression cotton varieties help to improve the mechanization of weed-control in Asian cotton production systems. This strategy will cost less than the conventional weed management methods, and promises to increase the economic gains of cotton farmers." Prof. ZHANG Rui added.