Grain Filling and Field Drying of a Set of Maize Hybrids Released From 1930 to 19821

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Abstract
Study of historically important cultivars may provide information on physiological traits that have been changed during selection for yield. Traits related to grain filling and drying were studied in commercially important maize (Zea mays L.) hybrids sold over the past 50 years. Hybrid studied were of approximately the same relative maturity and adapted to central Iowa. The duration of the grain filling period increased with year of release while grain filling rate was unchanged. The increase in grain filling duration was the result of later physiological maturity (black layer formation) rather than a change in flowering date. Late season plant health was improved in newer hybrids, which may have provided more viable leaf area to support prolonged grain filling. Grain drying rates were calculated by regression of water content·kernel−1 on heat units. Slopes of water loss were the same in the 2 years despite very different environmental conditions in the two seasons. Heat unit intercepts were different in the 2 years, with grain drying earlier in the hot, dry year of 1983. Grain water content at physiological maturity was correlated with year of release in 1983, but not in 1982. Several traits previously proposed to be associated with drying rate (husk number, date of husk death, ear angle, and number of kernel rows) were correlated with year of hybrid release. Correlation with drying rates over the season was significant for date of husk death in 1983.

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