Author
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LEWERS, KIM - IOWA STATE UNIVERSITY |
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ST MARTIN, S - OHIO STATE UNIVERSITY |
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HEDGES, B - PIONEER HI-BRED INTNL |
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PALMER, REID |
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Submitted to: Crop Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/15/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Soybean breeders often use soybean lines from other breeders to improve their own breeding program. The performance of the immediate progeny (hybrid) of a cross indicates which of the exotic lines are best for improving the breeding program. Until the recent development of the "cosegregation method" of hybrid soybean seed production, it has been difficult for breeders to produce enough seed of this hybrid generation to rely on the results of such an evaluation. Our objectives were 1) to use the cosegregation method to produce hybrid seeds, and 2) to compare the hybrid generation with the parental generation in order to 3) determine the relative utility of three generations (parental, first hybrid generations, and second hybrid generation) in evaluation of exotic soybeans. A secondary objective was to determine the usefulness in this evaluation process of two genes affecting stem growth. The study involved diverse soybean material and diverse testing environments, and several traits of importance to farmers were measured. The cosegregation method is the first of its kind to be used for evaluation of exotic lines of any crop, and it is hoped that this study will encourage breeders of other crops to use similar methods in this way. Neither of the two stem growth genes were necessary for soybean evaluation. A combination of data from the parental generation and the hybrid generations will allow breeders to identify exotic soybeans most likely to improve breeding programs. Comparisons of data from the first and second hybrid generations will allow breeders to select soybeans most likely to be useful toward development of commercial hybrid soybean. The findings from this study will be most useful to breeders interested in utilizing exotic soybeans or in commercialization of hybrid soybean. Technical Abstract: The F1 generation of a testcross previously has not been used to evaluate soybean [Glycine max (L.) Merr.] germplasm, primarily because production of large amounts of hybrid seed has been impractical, and because evaluation of one or a few plants gives irreproducible results. A novel method for efficiently producing testcross seed has been developed using the male- sterility locus, Ms6, and the seedling marker locus, W1. The objectives o this research were: 1) production and agronomic evaluation of testcross lines with their parental lines; 2) estimation of heterosis; 3) determination of the effects of the stem-type alleles, Dt2 and S, on the expression of vegetative and/or reproductive heterosis; and 4) determination of the utility of per se and testcross evaluation of germplasm. Two testers were used to genotypically evaluate the six lines. A randomized complete-block design (three-row plots, three replications, three locations, two years) compared the testcrosses with the parents for agronomic traits. Various heterosis values were calculated, and a three- factor analysis of variance determined the effects of the testers, the stem types, the lines to be evaluated, and interaction effects on the expression of heterosis. Significant F1 and F2 midparent heterosis and inbreeding depression, were observed for nearly all traits, including grain yield. The choice of tester was ascertained important in determining parental value of germplasm. The Dt2 and S alleles did not facilitate evaluations of germplasm through simultaneous manipulation of vegetative and reproductive heterosis. Parental lines were evaluated by using a combination of per se values, heterosis values and T1 values. The usefulness of these values for germplasm evaluation is discussed. |
