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Heterotic Performance and Combining Ability of Two-Way F₁ Soybean Hybrids¹

Eight attributes were measured in spaced F₁ soybean (Glycine max (L.) Merrill) hybrids and their parents. The F₁ hybrids gave an average of 13.4% heterosis for seed yield over their respective high parent in the 85 crosses evaluated. Nearly 77% of the hybrids exceeded the high parent yield. Seed size in large-seeded x large-seeded hybrids was nearly 4% smaller than the large parent, while in small-seeded x small-seeded crosses, the F₁'s and the larger-seeded parents had about the same average seed size. Thus, an increase in seed number was largely responsible for the increase in seed yield of the F₁. Wholeplant dry weight was larger and harvest index was smaller in the hybrids as compared with the high parent, indicating that, while the F₁'s produced more seed than the parents, their nonseed portion was unproportionately larger than in the parents. The hybrids approximated the midparent average in maturity, were generally shorter than the taller parent, and were not significantly different from the midparent mean in protein and oil contents.

Specific combining ability effects were significant for seed yield, maturity date, plant height, and oil content. Except for oil content, general combining ability estimates were significant and were two to six times larger than specific combining ability effects.

Key Words: Glycine max (L.) Merrill • Heterosis • General and specific combining ability

² Formerly Agronomist, Crops Research Division, and Professor, Iowa State University, Ames, Iowa (present address: Peterson Seed Company, Ames, Iowa); Research Associate (present address: University of Nebraska, Lincoln, Nebraska 68503); and Research Associate (present address: Soybean Research Project, Northrup, King and Co., Washington, Iowa, 52353).

Received for publication May 22, 1969.