Pollen-mediated gene flow in an autogamous crop: Foxtail millet (Setaria italica)

Abstract

Gene flow is a key concern associated with the contamination of seed multiplication fields and the use of transgenic crops. The release of herbicide-resistant germplasms and the use of male-sterile varieties make foxtail millet (Setaria italica) an appropriate material to investigate this concern. Pollen dispersal from pollen donor sources and gene flow in fertile and male-sterile varieties of foxtail millet were investigated in experiments in China and France. Although foxtail millet is mainly autogamous (less than 2% outcrossing), pollen from a 5 m diameter plot could fertilize a fertile variety up to 24 m away, and a male-sterile variety up to 40 m. Negative exponential and Weibull functions were used to fit the relationships between percentage and number of hybrids per cm of ear with distance from the pollen source. Wind velocity and direction resulted in variations of gene flow intensity, but did not change the slope of the regression equations. Pollen competition for available target ovules was observed up to 2 m away from a 1 m diameter pollen source. The percentage of pollen grains that fertilized ovules outside the pollen donor source was 1.4% of the total pollen grain production. For every 100 pollen grains released under field conditions 1.5 seeds were produced. The probability function of pollen dispersal for one donor plant was calculated. It allowed predictions of gene flow according to field shapes, estimations of isolation distances to preserve variety purity against pollen contamination, and the formulation of efficient male/female ratios for hybrid seed production.