POLLEN-MEDIATED GENE FLOW OF SULFONYLUREA-RESISTANT KOCHIA (KOCHIA-SCOPARIA)

The movement of sulfonylurea herbicide-resistant (R) kochia pollen was investigated in a spring barley field near Moscow, ID, using a Nelder plot design in 1991 and 1992. Each 61 m diameter plot had 16 rays spa ced 22.5 degrees apart and contained 211 kochia plants. There were 12 susceptible (S) plants and one R plant along each ray, The R and S pla nts were 1.5 m and 3.0 to 30.5 m from the center of the plot, respecti vely. Wind direction and speed in the 16 vectors, air and soil tempera ture, and rainfall were monitored continuously. Mature kochia seed was collected from individual plants, planted in the greenhouse, and spra yed with chlorsulfuron to test for resistant F-1 progeny. Results from the 2-yr study showed outcrossing of R pollen onto S plants at rates up to 13.1% per plant 1.5 m from the R plants and declining to 1.4 % p er plant or less 29 m from the R plants. At least 35% of the total R x S crosses occurred in the direction of prevailing southeastward winds . Predicted percentages of R x S crosses per plant ranged from 0.16 to 1.29 at 1.5 m, and 0.00 to 0.06% at 29 m. Thus, resistant kochia poll en can spread the sulfonylurea-resistant trait at least 30 m during ea ch growing season.