X hits on this document

PDF document

United States Department of Agriculture - page 13 / 36





13 / 36

SAMPLE PETITIONHerbicide-Tolerant Plants

D. Pollination of Cotton

Gossypium hirsutum is generally self-pollinating, but in the presence of suitable insect pollinators it can cross-pollinate. Bumble bees (Bombus spp.), Melissodes bees, and honey bees (Apis mellifera) are the primary pollinators (McGregor, 1976). Concentration of suitable pollinators varies from location to location and by season, and is considerably suppressed by herbicide 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 honeybee colonies, and movement of pollen was traced by means of fluorescent particles. At 150 to 200 feet from the source plants, 1.6 percent of the flowers showed the presence of the particles. The isolation distance for Foundation, Registered, and Certified seeds in 7 CFR Part 201 are 1,320, 1,320, and 660 feet, respectively.

Unlike G. hirsutum, G. tomentosum seems to be pollinated by lepidopterans, presumably moths (Fryxell, 1979). The stigma in G. tomentosum is elongated, so that 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.

E. Weediness of Cotton

Although the New World allotetraploids show some tendencies to “weediness” (Fryxell, 1979), the genus shows no aggressive, weedy tendencies in the South. Cotton is a poor competitor in most of the southern U.S. cotton-growing regions and is not allowed to overwinter. In more northerly areas where freezing conditions occur, the cotton plant cannot overwinter, and there is essentially no volunteerism from seed.

F. Modes of Gene Escape in Cotton

Genetic material of G. hirsutum may escape from a planting site by vegetative material, by seed, or by pollen.


Document info
Document views71
Page views71
Page last viewedFri Oct 28 23:39:43 UTC 2016