Pollen-mediated gene flow from blue aleurone wheat to other wheat cultivars

Cross-pollination among wheat (Triticum aestivum L.) cultivars historically has not been a major concern for wheat producers. However, with the introduction of genetically engineered wheat, there may be a need to ensure genetic purity, which will require knowledge of the frequency and distance that pollen-mediated gene flow can occur in wheat. This information will be necessary to develop (i) isolation distances that maintain predictable degrees of genetic purity in seed wheat production and (ii) practices to manage pollen-mediated gene flow in commercial wheat production. Field experiments were conducted from 2000 to 2003 at five locations in Oregon, Idaho, and Washington to determine the potential for pollen-mediated gene flow among winter wheat cultivars. Each experiment was designed as a Nelder wheel with 16 equally spaced rays extending away from a central pollen source of blue aleurone wheat. Each ray was 46 m long and contained two rows each of an early- and late-flowering soft white wheat cultivar. Seed samples were collected at 1.8-m intervals along each ray and examined for blue seed, which indicated successful hybridization with the pollen source. Although blue seed was found in some samples at all five locations, most samples (98%a) contained no blue seed. Pollen-mediated gene flow generally was in the direction of the prevailing wind and tended to occur more often at the sites with lower temperature and higher humidity during pollination. The maximum distance that gene flow was detected was 42 m from the pollen source and the maximum outcrossing in an individual sample was 0.45%. At four locations, no outcrossing was detected beyond 30 m from the pollen source; however, at one site, 13% of the blue seed was found between 30 and 42 m. Pollen-mediated gene flow potential may differ for other wheat cultivars and environmental conditions. Depending on the required genetic purity standards for wheat seed, an isolation distance of 45 m or more may be required.