POLLEN-MEDIATED GENE FLOW IN AN AUTOGAMOUS CROP - FOXTAIL MILLET (SETARIA-ITALICA)

Gene how is a key concern associated with the contamination of seed mu ltiplication fields and the use of transgenic crops. The release of he rbicide-resistant germplasms and the use of male-sterile varieties mak e foxtail millet (Setaria italica) an appropriate material to investig ate this concern. Pollen dispersal from pollen donor sources and gene flow in fertile and male-sterile varieties of foxtail millet were inve stigated in experiments in China and France. Although foxtail millet i s mainly autogamous (less than 2% outcrossing), pollen from a 5 m diam eter plot could fertilize a fertile variety up to 24 m away, and a mal e-sterile variety up to 40 m. Negative exponential and Weibull functio ns were used to fit the relationships between percentage and number of hybrids per cm of ear with distance from the pollen source. Wind velo city and direction resulted in variations of gene how intensity, but d id not change the slope of the regression equations. Pollen competitio n for available target ovules was observed up to 2 m away from a Im di ameter pollen source. The percentage of pollen grains that fertilized ovules outside the pollen donor source was 1.4% of the total pollen gr ain production. For every 100 pollen grains released under field condi tions 1.5 seeds were produced. The probability function of pollen disp ersal for one donor plant was calculated. It allowed predictions of ge ne flow according to field shapes, estimations of isolation distances to preserve variety purity against pollen contamination, and the formu lation of efficient male/female ratios for hybrid seed production.