<p style="text-align: justify;">Cotton (<i>Gossypium hirsutum</i> L.) was grown commercially in over 80 countries with a combined production of 44.2 million metric tonnes of cotton seed and 24.8 million metric tonnes of cotton lint in 2006. The major producers of cotton seed and lint were China, the United States, India, Pakistan, Brazil, Uzbekistan and Turkey. Cotton is primarily grown for its seed bolls that produce fibres used in numerous textile products.</p>

<p style="text-align: justify;">About two thirds of the harvested cotton crop is seed, which is separated from the lint during ginning. The cotton seed is crushed to produce cottonseed oil, cottonseed cake (meal), and hulls. Cottonseed oil is used primarily as a cooking oil, in shortening, margarine and salad dressing, and is used extensively in the preparation of snack foods such as crackers, cookies and chips. The meal and hulls are an important protein concentrate for livestock, and may also serve as bedding and fuel. Linters, or fuzz, which are not removed in ginning, are used in felts, upholstery, mattresses, twine, wicks, carpets, surgical cottons, and in industrial products such as rayon, film, shatterproof glass, plastics, sausage skins, lacquers, and cellulose explosives.</p>

<p style="text-align: justify;">Effective weed management is critical to cotton production. Weed control is more difficult in cotton than in other row crops, such as corn or soybean; cotton grows slowly early in the growing season and is thus less competitive with weeds. Competition from weeds has negative impacts on crop establishment, and ultimately, on crop yield. Weeds can also be detrimental later in the growing season, interfering with harvesting, and resulting in a reduction in lint quality due to trash and possible staining. Weed control strategies include pre-plant tillage, crop rotation, and the use of herbicides. Annual grasses and some small seed broadleaf weeds typically are controlled with preplant incorporated herbicides (e.g., trifluralin, norflurazon, pendimethalin) while most broadleaf species are controlled with postemergence herbicides (e.g., fluometuron, pendimethalin, pyrithiobac sodium). Crop rotation (e.g., with soybean) prevents the build-up of problem weeds, and herbicide resistant biotypes by allowing the use of different herbicides.<br />
The cotton line LLCotton25 was developed to allow the use of glufosinate ammonium (trade name Liberty&reg;), as a weed control option in cotton production. The herbicidal mode of action of glufosinate ammonium is related to the activity of glutamine synthetase (GS), the enzyme required for the synthesis of the amino acid glutamine. L-phosphinothricin, the active ingredient of glufosinate ammonium, is a structural analog of glutamate, and acts as a competitive inhibitor. After application of the herbicide, L-phosphinothricin competes with glutamine for its active sites on GS. The results of the inhibition of GS are an accumulation of ammonia in the plant, a reduction in the synthesis of glutamine, and an inhibition of photosynthesis. This causes the death of plant cells, and eventually, the entire plant. This genetically engineered cotton line LLCotton25 contains the bar gene, which codes for the production of the enzyme phosphinothricin acetyl-transferase (PAT). This enzyme acetylates glufosinate ammonium, rendering it inactive in the plant. The expression of the bar gene in LLCotton25 allows it to survive the otherwise lethal application of glufosinate ammonium. The <i>bar</i> gene was isolated from <i>Streptomyces hygroscopius</i>, a gram-positive soil bacterium.<br />
LLCotton25 was developed by <i>Agrobacterium</i>-mediated transformation of the cotton variety &lsquo;Coker312&rsquo; with a plasmid vector containing the <i>bar</i> gene. Whole plants were treated with glufosinate ammonium and successful transformants were detected by selecting plants that had not exhibited the phytotoxic effects of glufosinate ammonium<br />
LLCotton25 was field tested in the United States and Puerto Rico at 43 locations over three years (1999-2001). The data from these field trials showed that LLCotton25 did not differ significantly, in terms of plant morphology, growth, agronomic performance, and susceptibility to diseases and pests, from the nontransformed parent &lsquo;Coker 312.&rsquo; LLCotton25 did not exhibit any increased tendency towards weediness, compared to the unmodified parental line. This was demonstrated by nonsignificant differences in parameters such as seed germination, seedling vigour, time to first bloom, and plant maturity, which affect the reproductive fitness and competitiveness of a plant. The impact on beneficial and nontarget organisms from the cultivation of LLCotton25 was similar to that of its unmodified parental line and conventional cotton cultivars. These results also led to the conclusion that the cultivation of LLCotton25 would not be expected to impact threatened or endangered species.</p>

<p style="text-align: justify;">Cotton plants are primarily self-pollinating, but insects, especially bumblebees and honeybees, also distribute cotton pollen. Cotton can cross-pollinate with compatible species including <i>G. hirsutum</i> (wild or under cultivation) and <i>G. barbadense</i> (cultivated Pima cotton), and is genetically compatible with <i>G. tomentosum</i>. Overall, the probability of gene transfer to wild species in unmanaged ecosystems is low due to the relatively isolated distribution of <i>Gossypium</i> species, different breeding systems, and genomic incompatibility. Assuming proximity, synchronicity of flowering and presence of insects, LLCotton25 could freely hybridize with other <i>G. hirsutum</i> varieties and wild plants.</p>

<p style="text-align: justify;">The food and livestock safety of LLCotton25 was established based on: the fact that PAT protein constitutes a small amount of the total protein in LLCotton25, so there is little dietary exposure; the determination that the introduced gene and the novel protein are unlikely to be toxic or allergenic; and,<i> in vitro</i>, <i>in vivo</i> and other safety studies (e.g., intravenous and feeding studies) conducted in the laboratory using PAT protein. The nutritional equivalence of LLCotton25, compared to its untransformed parent line, was demonstrated by the analysis of key nutrients, including: protein, crude fat, ash, crude fibre, ADF, NDF, amino acid, fatty acids, minerals, vitamin E, as well as anti-nutrients. The equivalence of LLCotton25 to conventional cotton, in terms of livestock feed, was confirmed in feeding studies conducted with broiler chickens.</p>

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