Gene flow between Gossypium hirsutum L. and Gossypium barbadense L. is asymmetric

Abstract

As both Pima cotton (Gossypium barbadense L.) and Acala (Upland; G. hirsutum L.) are grown in the southwestern United States, understanding gene fl ow within and among these species is important to maintain genetic purity. In small scale and commercial fi elds, gene fl ow decreased exponentially from 1.44% at 1 m to less than 0.50% at 10 m in Acala cotton. Corresponding values for Pima cotton were 0.19% at 3 m and 0% at 10 m or beyond. When interspecies outcrossing occurred, Pima cotton was preferentially pollinated by Acala cotton. Gene fl ow was nondetectable in 7.5 m borders. Asymmetric pollination between Acala and Pima cotton was also observed in samples collected in borders located 6 m from the pollen source with no detectable gene fl ow beyond 7.5 m. At a given distance, in commercial scale Pima fi elds, gene fl ow was tenfold less than reported in Acala fi elds with gene fl ow not exceeding 0.43% beyond 10 m. No gene fl ow was detected beyond 800 m (0.5 mile). This study indicates that isolation distances can be shorter in Pima cotton than in Acala cotton to maintain the same level of genetic purity. Comparison with historical evidence suggests that there has been a shift in the relative gene fl ow among species in modern cultivars of Pima cotton. © Crop Science Society of America.