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Ear to Row Selection for Early Maturity in Sweet Corn¹

A short season, uniform, and high quality variety sweet corn (Zea Mays L.) was sampled for genes influencing early maturity by combination with a series of established inbred lines, followed by self-pollination and ear to row selection through the S₆ generation. In each of two years, maturity was further evaluated by use of remnant seed in replicated trials. Maturity was measured on a calendar day and thermal unit basis.

At the S₁, but not at the F₁, there was a significant correlation with the maturity of later generations in both the nursery and trials. When remnant seed of successive generations was planted in the same year, variation in maturity between generations was reduced markedly. While use of thermal units did not increase the consistency among generations within a trial year, their use minimized differences between years. The analysis of variance showed highly significant differences for trial years, generations, families, years x families, generations families, and years x generations x families. Differences between generations and families were more marked in the unusually warm 1964 season. Separate analysis for generations showed a consistent decrease in replicate variation and within plot variability and an increase in significance of yearly differences as homozygous increased. Change in maturity during inbreeding and selection, expressed as per cent of the initial seed parent, was greater for strains which ultimately achieved comparative early maturity. Fluctuation in maturity across generations as measured by the coefficient of variation was not significantly related to actual maturity. There was a general delay in maturity with generation of breeding from the S₁ to S₅, resulting in an average regression coefficient of 14.3 thermal units per generation. For the families included in this study there was an average shortening in maturity of 4.7 per cent for the derived over the original lines with four families showing a shortening in excess of 12 per cent.

Key Words: Silking date • Thermal units • Generation • Consistency • Correlation • Regression coefficient

² Professor of Agronomy, University of Wisconsin, Madison, Wis. 53706.

Received for publication May 15, 1968.