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Managing Reproductive Isolation in Hybrid Seed Corn Production

^a Doebler's Pennsylvania Hybrids, Inc., daleireland{at}doeblers.com
^b Landec Ag, Inc. 201 N. Michigan, Oxford, IN 47971, dwilson{at}landecag.com
^c Department of Agronomy, Iowa State University, Ames, IA 50011
^d Burris Consulting 1707 Burnett Ave, Ames, IA 50010, burrisconsulting{at}msn.com
^e Pioneer Hi-Bred International, Inc., 6900 NW 62nd Avenue, Johnston, IA 50131, Michael.Lauer{at}Pioneer.com

View larger version (62K): [in a new window]   Fig. 1. Diagram of sampling transect within a seed production field relative to an adventitious pollen source. Selected seed fields were adjacent to an adventitious pollen source that overlapped at least 50% of the seed field to the North, East, South, or West. Sampling transects were located on the side of the field adjacent to the adventitious pollen source. Ears were collected along the transect at 1.8 m (6 ft), 9.4 m (31 ft), 20.6 m (68 ft), 35.8 m (118 ft), and 200 m (660 ft) from the field edge nearest to the adventitious pollen source. Blocked area surrounding the seed field indicates border rows, which varied in number with distance between seed field and adventitious pollen source.

View larger version (33K): [in a new window]   Fig. 2. Distribution of out-crossing values and management variables for the 315 seed production fields analyzed from 1998 to 2000. A: out-crossing values for all sampling locations. B: isolation distances between seed fields and nearest adventitious pollen source. C: seed field sizes. D: adventitious pollen source field sizes. E: number of border rows. F: male/female row ratios. Distributions of the management variables (B–F) were used to define predictor classes for comparison of out-crossing percentages at the field margins and field midpoints.

View larger version (14K): [in a new window]   Fig. 3. Relationship between Number of Border Rows and Isolation Distance for 315 seed production fields included in this study. Many points are obscured because of common values in the data.

View larger version (23K): [in a new window]   Fig. 4. Mean out-crossing levels observed at each field sampling location in 1998, 1999, and 2000. Samples were collected at 1.8 m (6 ft), 9.4 m (31 ft), 20.6 m (68 ft), 35.8 m (118 ft), and 200 m (660 ft) from the field edge nearest to the adventitious pollen source. Data are the mean for 60 field transects in 1998, 93 transects in 1999, and 162 transects in 2000. The Y-axis error bars represent the 90% CI. Plotted distances are offset each year for clarity.