Inheritance of emergence time and seedling growth at low temperatures in four lines of maize

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Abstract
The improvement of rate of seedling emergence and early seedling growth of maize (Zea mays L.) under cool conditions has been an objective of breeding programs in cool regions for many years. To study inheritance of emergence time, and to determine if differences in emergence time were due to differences in seedling growth, F1, F2 and backcross generations of a diallel cross of two rapidly emerging lines from CIMMYT Pool 5, 5-113 and 5-154, and two elite Corn Belt Dent lines, A619 and A632, were grown in controlled environment rooms at low temperatures. The lines from Pool 5 emerged significantly faster than A619 and A632 over a range of low temperature conditions. This difference occurred both when the lines themselves were tested and when the lines were tested as male and female parents in crosses. The Pool 5 lines converted a higher proportion of their original seed to new root and shoot tissue than did A619 and A632, indicating that they had a faster seedling growth rate. Primarily this was due to a faster loss of seed reserve, rather than a more efficient conversion process. A significant difference occurred between A619 and A632 for emergence time, but this was not due to a difference in seedling growth rate. Reciprocal differences occurred only in the F1 generation in crosses involving A619, and then marked effects could be attributed to the male parent. Reciprocal differences tended to disappear in the F2. This suggested that the genotype of the embryo and endosperm was of much greater importance than the genotype of the maternal parent in determining differences of time to emergence and seedling growth. Mid-parent heterosis occurred for time to emergence and seed loss, a measure of mean rate of utilization of seed reserve, in all crosses. High parent heterosis occurred in several crosses for these traits. High parent heterosis occurred in all crosses for efficiency of utilization of seed reserve. A generation means analysis indicated that both additive and dominance effects were present for rate of seedling growth in crosses between A632 and the Pool 5 lines.