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Abstract
Male-sterility systems combined with insect-mediated cross-pollination in soybean [Glycine max (L.) Merr.] have been shown to produce large quantities of hybrid seed, which can be useful for studying heterosis and agronomic performance in different population types. The procedure was used to obtain large quantities of hybrid seed for replicated yield trials. The objective of our study was to evaluate agronomic performance of soybean single, three-way, four-way, and five-way crosses, and three backcross generations (BC1, BC2, and BC3) to estimate heterosis for yield and other agronomic traits. Parental genotypes were male-sterile, female-fertile lines, selected for excellent insect pollinator attraction, crossed to a group of male parents selected for their agronomic performance. In 2003, F1 seed of single crosses were evaluated in replicated experiments at two locations in Iowa and one location in Indiana. In 2004, three-way crosses and BC1 populations were evaluated at one location in Iowa. In 2005, hybrid seed of single, three-way, and four-way crosses, BC1, and BC2 populations of eight families were planted at one location in Iowa. In 2006, the five-way crosses and BC3 populations were planted at one location in Iowa. In all experiments, hybrids and parents were evaluated. Results showed a range in mid-parent heterosis values (MPH) for yield from −35% to +42%, and in high-parent heterosis (HPH) from −44% to +42%. For yield, backcross populations had higher heterosis estimates than the other population types. For seed protein content, mean MPH ranged from −1% to +7%, and mean HPH from −4% to +7%. For oil content, mean MPH ranged from −10% to +6%, and mean HPH from −13% to +3%. Negative heterosis values were observed, indicating that a large number of different parental combinations need to be evaluated to identify the superior heterotic combinations. These evaluations will determine the feasibility of hybrid soybean production for commercial purposes.
We are grateful to Gregory Gebhart for help with planting and harvest. Thanks also to Dairyland Seed Co. Inc. and Verde Seed Co. Inc. for partial support of this project.
This is a joint contribution from the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project 4403, and from the USDA, Agricultural Research Service, Corn Insects and Crop Genetics Research Unit, and supported by the Hatch Act and the State of Iowa. The mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by Iowa State University or the USDA, and the use of the name by Iowa State University or the USDA implies no approval of the product to the exclusion of others that may also be suitable.