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Second Phase in the Evaluation of Synthetic Varieties of Maize for Yield¹

The second phase of a sequential synthetic variety testing program for yield in maize {Zea mays L.) is reported. Four varieties selected from the tests of the first phase and five previously untested varieties were crossed in a diallel series and evaluated at three locations in each of two years.

The yield level of the varieties included for the first time was generally higher than those selected from the first phase. Two-ear Syn., Syn. AA, and Syn. BB were the highest-yielding varieties, whereas S.S. Syn. and Purdue MJ yielded significantly lower than the other varieties. S.S. Syn. was outstanding in cross performance; it had the highest average yield in crosses and a significant, positive general combining ability effect. Two-ear Syn. was high in both variety and cross performance and had the largest variety effect (
= 3.44**).

Relative to the midparent and high parent, average heterosis for all crosses was 9.8 and 4.2%, respectively. Relative to the high parent, S.S. Syn., L.E. Syn., and C.B. Syn. j3 exhibited the most heterosis in crosses. S.S. Syn. x Pa- Int- Syn. had a significant, specific heterosis effect (
= 5.51**) and an observed heterosis of 24.1% relative to the midparent. Very little heterosis was observed for the crosses involving Syn. AA and Syn. BB. Specific heterosis (s.c.a.) was significant (P < .05) in the combined analysis. The specific effects for only three crosses were larger than the standard error: S.S. Syn. x Pa. Int. Syn. had a positive effect, and Syn. AA x Pa- Int. Syn. and Syn. BB x S.S. Syn. significant, negative effects. The cross, S.S. Syn. x Pa- Int- Syn., was the highest yielding in both phases of testing.

Key Words: diallel • variety crosses • heterosis • combining ability

² Research Geneticist, Crops Research Division, ARS, USDA, and Agriculture Research Technician, respectively.

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