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Plant Density Effects on Combining Abilities of Early Maize Synthetics¹

Five early maize (Zea mays L.) synthetics were evaluated for general combining ability (GCA), specific combining ability (SCA), average heterosis, and reciprocal effects to estimate the optimum plant density for combining ability analysis in early improved synthetics, and the importance of reciprocal differences in early maize synthetics. Yield and agronomic data were obtained for the five parental synthetics and 20 synthetic crosses grown at 45,500, and 57,000, and 67,500 plants/ha in each of four environments.

The absence of GCA interactions with plant densities indicated that a single density within the range of those tested should adequately evaluate these synthetics. Significant reciprocal effects for ear moisture at harvest, kernel depth, and kernel rows/ear indicated that cytoplasmic effects were important in these synthetics. Reciprocal differences of more than 3% for ear moisture at harvest between synthetic crosses indicated careful choice of the female parent could be a means of reducing crop drying costs and facilitating earlier harvest.

The absence of detectable SCA effects for these synthetics indicated inter-population improvement methods would not be advantageous within this group of synthetics.

Average heterosis for grain yield in this study was 10.7%. This heterosis can be attributed to increased kernel size and kernel number which is consistent with the idea that heterosis may be produced by an increased effective filling period duration (EFPD).

Key Words: Genotype x environment interactions • Heterosis • Reciprocal effects • Yield components • Zea mays L.

² Professors of agronomy, North Dakota State University, Fargo, ND 58105.

Received for publication June 15, 1981.