EFFECTS OF THE DT2 AND S ALLELES ON AGRONOMIC TRAITS OF SOYBEAN INBRED AND HYBRID GENOTYPES

Authors: LEWERS, KIM - IOWA STATE UNIVERSITY; ST MARTIN, S - OHIO STATE UNIVERSITY; HEDGES, B - PIONEER HI-BRED INTL; PALMER, REID

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Evaluation of the first (hybrid) generation of a cross between two soybean lines allows a breeder to determine if one line has genes that compliment the other and should be used in a breeding program. This is called testcross evaluation and is useful for adding genetic diversity to an established gene program. Hybrid soybeans have been reported to grow very tall and fall over (lodge) possibly resulting in reduced grain yield. Two genes affecting stem growth, the Dt2 and S genes, were tested to determine if they could reduce lodging and maintain grain yield in hybrid soybean. In addition we evaluated the consistency of the effects of the two genes across different genetic backgrounds. Consistency of effect would be important for the genes to be useful in testcross evaluation. Several traits were evaluated. The study included locations in Iowa, Ohio, and Ontario. We found that the Dt2 and S genes have the same effects on the hybrid generation that they have on the parental generation, but that the effects are not consistent in degree across genetic backgrounds. We determined that the S gene may be valuable in commercial hybrid soybean, because it reduces lodging without reducing grain yield or altering seed protein or oil percentage. We also determined that neither the Dt2 nor the S gene would be useful if present in a tester line used in testcrosses. This information is useful to private and public soybean breeders who incorporated unadapted lines into their breeding programs. It will save them the time and effort required to backcross these genes into their tester lines. This information also will be of interest to those who are exploring the potential of commercialization of hybrid soybean. They may choose to include the S gene in hybrid soybean when and if developed.

Technical Abstract: Agronomic evaluation of hybrid soybean [Glycine max (L.) Merr.] will be useful for germplasm evaluation, recurrent selection, and estimating heterosis. Vegetative heterosis, commonly observed in soybean, could increase early lodging and pod abortion, reducing grain yield. The Dt2 and S alleles have been shown to reduce excessive vegetative growth and lodging gin narrow-row production of inbred soybean. The objectives of this research were to determine the effects of the Dt2 and S alleles on hybrid soybean, to assess their potential in facilitating germplasm evaluation and recurrent selection, and to determine if they would be desirable in commercialized hybrid soybean. Two sets of near-isogenic inbred lines and 14 sets of near-isogenic hybrid (F1) lines were evaluated to determine the effects of the Dt2 and S alleles on agronomic traits. The study was factorial with three factors: pollen parents, pod parents, and stem type. A randomized complete-block design was used; entries were the inbred sets, and hybrid sets. Evaluations were made on replicated three-row plots at three locations for two years. Traits evaluated include maturity date, lodging, plant height, harvest index, seed yield, 100-seed weight, seed protein content, and seed oil content. The Dt2 and S alleles affected agronomic traits of hybrids and inbreds similarly. The Dt2 and S alleles hastened maturity, decreased plant height and lodging, and increased harvest index. The Dt2 allele decreased seed weight and protein content. Interactions effects of stem type and genotype were observed for plant height, grain yield, and harvest index. The data suggest that the Dt2 and S alleles would not be consistently beneficial to germplasm evaluation or recurrent selection, but might be useful for commercial hybrid soybean.