“Glufosinate is a broad-spectrum, non-selective, foliar herbicide that effectively controls many grass and broadleaf weeds.

“Phosphinothricin, the active portion of the glufosinate molecule, inhibits the enzyme glutamine synthetase. Glutamine synthetase is the initial enzyme in the pathway that assimilates inorganic nitrogen into organic compounds. Glutamine synthetase is pivotal in nitrogen metabolism converting ammonia and glutamic acid into glutamine.

“Since plants detoxify ammonia almost exclusively through this pathway, glufosinate causes the accumulation of ammonia accompanied by cessation of photosynthesis, disruption of chloroplast structure, and vesiculation of the stroma,” Culpepper says.

The primary source of LibertyLink cotton tolerance to glufosinate is a mechanism based on metabolic inactivation of Ignite herbicide.

The glufosinate resistant BARgene of Streptomyces hygroscopicus and PATgene of Streptomyces viridochromogenes encode for phosphinothricin-acetyltransferase, an enzyme which converts L-phosphinothricin that kills plants to non-lethal N-acetyl-L-phosphinothricin.

A similar PAT gene is used in Widestrike cotton primarily to allow scientists to track the movement of the gene used to make these cotton varieties non-palatable to a wide range of insect pests that commonly feed on cotton.

Though not an exact copy, the PAT gene in Phytogen Widestrike cotton does make cotton plants tolerant of glufosinate-based herbicides, including Ignite, which is part of the LibertyLink system marketed by Bayer CropScience.

Long-time Cotton Agronomist Johnny Parker, who works for Continental Cotton Gin in Windsor, Va., says telling Virginia cotton growers not to use Ignite on Widestrike cotton is a good way to lose credibility.

“They have been using it for years, it works, it provides another good tool for managing weeds and grasses and there have been few problems with it.