<p style="text-align: justify;"><big><b>Cotton as a Crop</b></big></p>

<p style="text-align: justify;">Four species of the genus Gossypium are known as cotton, which is grown primarily for the seed hairs that are made into textiles. Cotton is predominant as a textile fiber because the mature dry hairs twist in such a way that fine, strong threads can be spun from them. Other products, such as cottonseed oil, cake, and cotton linters are byproducts of fiber production. Cotton, a perennial plant cultivated as an annual, is grown in the United States mostly in areas from Virginia southward and westward to California, in an area often referred to as the Cotton Belt (McGregor 1976).</p>

<p style="text-align: justify;"><big><b>Taxonomy of Cotton</b></big></p>

<p style="text-align: justify;">The genus Gossypium, a member of the Malvaceae, consists of 39 species, four of which are generally cultivated (Fryxell, 1984). The most commonly cultivated species, <i>G. hirsutum</i> L., is the subject of this EA. Other cultivated species are <i>G. arboreum</i> L., <i>G. barbadense</i> L., and <i>G. herbaceum</i> L. Four species of Gossypium occur in the United States (Fryxell 1979; Kartesz and Kartesz 1980). <i>Gossypium hirsutum</i> is the primary cultivated cotton. Gossypium barbadense is also cultivated. The other two species, <i>G. thurberi</i> Todaro and <i>G. tomentosum</i> Nuttall ex Seemann, are wild plants of Arizona and Hawaii, respectively. <i>Gossypium tomentosum</i> is known from a few strand locations very close to the ocean.</p>

<p style="text-align: justify;"><big><b>Genetics of Cotton</b></big></p>

<p style="text-align: justify;">At least seven genomes, designated A, B, C, D, E, F, and G, are found in the genus (Endrizzi 1984). Diploid species (2n=26) are found on all continents, and a few are of some agricultural importance. The A genome is restricted in diploids to two species (<i>G. arboreum</i>, and <i>G. herbaceum</i>) of the Old World. The D genome is restricted in diploids to some species of the New World, such as <i>G. thurberi</i>. By far, the most important agricultural cottons are <i>G. hirsutum</i> and <i>G. barbadense</i>. These are both allotetraploids of New World origin, and presumably of ancient cross between Old World A genomes and New World D genomes. How and when the original crosses occurred have been subject to much speculation. Euploids of these plants have 52 somatic chromosomes, and are frequently designated as AADD. Four additional New World allotetraploids occur in the genus, including <i>G. tomentosum</i>, the native of Hawaii. <i>Gossypium tomentosum</i> has been crossed with <i>G. hirsutum</i> in breeding programs. The New World allotetraploids are peculiar in the genus, because the species, at least in their wild forms, grow near the ocean, as invaders in the constantly disturbed habitats of strand and associated environs. It is from these &quot;weedy&quot; or invader species that the cultivated cottons developed (Fryxell 1979).</p>

<p style="text-align: justify;"><big><b>Pollination of Cotton</b></big></p>

<p style="text-align: justify;"><i>Gossypium hirsutum</i> is generally self-pollinating, but in the presence of suitable insect pollinators can exhibit cross pollination. Bumble bees (Bombus spp.), Melissodes bees, and honey bees (<i>Apis mellifera</i>) are the primary pollinators (McGregor 1976). Concentration of suitable pollinators varies from location to location and by season, and is considerably suppressed by insecticide use. If suitable bee pollinators are present, distribution of pollen decreases considerably with increasing distance. McGregor (1976) reported results from an experiment in which a cotton field was surrounded by a large number of honey bee colonies, and movement of pollen was traced by means of fluorescent particles. At 150 to 200 feet, 1.6 percent of the flowers showed the presence of the particles. The isolation distance for Foundation, Registered, and Certified seed in 7 CFR Part 201 is 1320 feet, 1320 feet, and 660 feet, respectively. Research in Mississippi shows that pollen movement decreases rapidly after 40 feet (12 meters). Umbeck <i>et al</i>. (1991) studied pollen and successful gene movement of cotton in Mississippi test plots. Around a central transgenic test plot of 98,800 plants with rows running north-south, they planted 23 one-meter border rows of nontransgenic cotton to the east and to the west, and 25 meters of non transgenic cotton border rows to the north and to the south, each divided into two 12.5 meter long plots. The border rows to the north and south were continuous with the transgenic rows. They took 32,187 seed samples from all border rows at bottom, middle, and top plant position (representing seasonal variation) and used a kanamycin resistance marker gene to test for seeds resulting from pollen movement out of the central transgenic plot. To the east and west, gene movement at the first row was 0.057 and 0.050, and dropped rapidly to row 8, and was not detected in subsequent rows to the east, and detected occasionally at &lt;0.01 in rows to the west. Combined data for east and west border rows beyond row 9 gave total outcrossing of 0.0012. To the north and south, detections were totaled for each 12.5 meter block and gave figures of 0.0053 and 0.0047 for north and south inner block and 0.0015 and 0.0021 for north and south outer block. <i>Gossypium tomentosum</i> seems to be pollinated by lepidopterans, presumably moths (Fryxell 1979). The stigma in <i>G. tomentosum</i> is elongated, and the plant seems incapable of self-pollination until acted upon by an insect pollinator. The flowers are unusual too, because they stay open at night; most Gossypium flowers are ephemeral: they open in the morning and wither at the end of the same day.</p>

<p style="text-align: justify;"><big><b>Weediness of Cotton</b></big></p>

<p style="text-align: justify;">Although the New World allotetraploids show some tendencies to &quot;weediness&quot; (Fryxell 1979), the genus shows no particular weedy aggressive tendencies.</p>

<p style="text-align: justify;"><big><b>Modes of Gene Escape in Cotton</b></big></p>

<p style="text-align: justify;">Genetic material of <i>G. hirsutum</i> may escape from a test area by vegetative material, by seed, or by pollen. Propagation by vegetative material is not a common method of reproduction of cotton. Physical safeguards that inhibit the movement of vegetative material from the area should be adequate to prevent gene movement by this means. Movement of seed from the test area can likewise be inhibited by adequate physical safeguards. Movement of genetic material by pollen is possible only to those plants with the proper chromosomal type, in this instance only to those allotetraploids with AADD genomes. In the United States, this would only include <i>G. hirsutum</i>, <i>G. barbadense</i>, and <i>G. tomentosum</i>. <i>Gossypium thurberi</i>, the native diploid from Arizona with a DD genome, is not a suitable recipient. Movement to <i>G. hirsutum</i> and <i>G. barbadense</i> is possible if suitable insect pollinators are present, and if there is a short distance from transgenic plants to recipient plants. Physical barriers, intermediate pollinator-attractive plants, and other temporal or biological impediments would reduce the potential for pollen movement. Movement of genetic material to <i>G. tomentosum</i> is more unknown. The plants are chromosomally compatible with <i>G. hirsutum</i>, but there is some doubt as to the possibility for pollination. The flowers of <i>G. tomentosum</i> seem to be pollinated by moths, not bees. And they are receptive at night, not in the day. Both these factors would seem to minimize the possibility of cross-pollination. However, Fryxell (1979) reports that <i>G. tomentosum</i> may be losing its genetic identity from introgression hybridization of cultivated cottons by unknown means.</p>

<p><big><b>Literature Cited</b></big></p>

<ol>
	<li>Endrizzi, J. E., Turcotte, E. L., and Kohel, R. J. 1984. Qualitative Genetics, Cytology, and Cytogenetics. pp. 82-129. In Kohel, R. J. and Lewis, C. F., Editors. Cotton. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. Madison, Wisconsin. 605 pp.</li>
	<li>Fryxell, P. A. 1979. The Natural History of the Cotton Tribe (Malvaceae, Tribe Gossypieae). Texas A&amp;M University Press. College Station and London. 245 pp.</li>
	<li>Fryxell, P. A. 1984. Taxonomy and Germplasm Resources. pp. 27-57. In Kohel, R. J. and Lewis, C. F., Editors. Cotton. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. Madison, Wisconsin. 605 pp.</li>
	<li>Umbeck, P. F., Barton, K. A., Nordheim, E, V., McCarty, J. C, Parrott, W. L., and Jenkins, J. N. 1991. Degree of Pollen Dispersal by Insects from a Field Test of Genetically Engineered Cotton. <i>J. Econ. Entomology</i> <b>84</b>:1943-1991.</li>
	<li>Kartesz, J. T., and Kartesz, R. 1980. A Synonymized Checklist of the Vascular Flora of the United States, Canada, and Greenland. The University of North Carolina Press. Chapel Hill.</li>
	<li>McGregor, S. E. 1976. Insect Pollination of Cultivated Crop Plants. Agriculture Handbook No. 496. U.S. Government Printing Office. Washington, DC.</li>
</ol>

<p><big><b>Credits</b></big></p>

<p>James Lackey, Ph.D. Botanist USDA, APHIS, BBEP BIOTECHNOLOGY PERMITS email: <a class="main" href=" mailto:jlackey@aphis.usda.gov">jlackey@aphis.usda.gov</a></p>
