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Heterosis and Combining Ability in Exotic Soybean Germplasm¹

The objectives of this study were to determine the magnitude of heterosis for yield, its components, and other agronomic characters and to determine the relative importance of general combining ability (GCA) and specific combining ability (SCA) in spaced plants soybean [Glycine max (L.) Merr.] hybrids with both adapted cultivars and exotic strains as parents.

The experiment, conducted at West Lafayette, Ind. in 1971 and 1972, used a partial diallel mating design with 12 parents. There were three parents from each of the following origins; locally adapted cultivars or strains, Manchurian, Chinese, and Korean. Thirty different F₁ combinations were produced and, along with their parents, planted in a randomized, complete block design.

Heterosis for yield was greater than that for any other character with a high-parent value of 8.0% averaged over both years. Twelve of the 30 hybrids outyielded the midparent. Number of pods/plant was the most heterotic of the yield components. Number of seeds/pod and seed size of the F_l's was with few exceptions, intermediate to parental values, as were maturity, height, lodging, and harvest index. Heterosis for plant weight was similar to that for yield, both in magnitude and in the hybrids expressing it.

Significant GCA effects were found for all characters. SCA effects were significant for seed size, maturity, and height. The years x GCA interaction was significant for yield, number of pods/plant, maturity, lodging score, plant weight, and harvest index. Years x SCA were significant for ntunber of seeds/pod, maturity, lodging, and harvest index.

Key Words: Partial diallel • Glycine max • Genetic diversity

² Assistant professor of plant breeding (international) U. of Ill., stationed at the U. of Puerto Rico, Mayaguez, research geneticist and professor of agronomy, Purdue U., West Lafayette, IN 47907.

Received for publication October 7, 1974.