Assimilate supply (source) reportedly limits grain yields (sink) of early-maturing maize (Zea mays L.) hybrids. This field research sought to determine if selecting for high average leaf expansion rates (ALER) in early maize could increase leaf area without delaying maturity. Combining abilities of S2 (second selfed generation) lines with differing ALER values were estimated for ALER, leaf area/plant, silking date, leaf number, length and width, and ear and cob dimensions. The S2 hybrids were selected to represent a 2 X 2 factorial arrangement of ALER types (HER = high ALER and LER = low ALER). Two groups (GI and GII) of lines were selected from S2 lines previously rated using the formula ALER = (leaf number X ear leaf length X ear leaf width X 0.75)/(d to pollination). Four sets of lines with differing ALER ratings were paired by source population, year evaluated, and silking date. Within each set, the four S2 lines from GI were crossed to the four S2 lines from GII to produce 16 hybrids representing a 2 X 2 factorial arrangement of four hybrids each of HER X HER, HER X LER, LER X HER, and LER X LER classes. Field experiments arranged in simple lattice designs were grown with two replicates for each of seven environments. Averaged across environments, hybrids from HER parents in both GI md GII had significantly higher ALER, due to more leaf area/plant. The HER hybrids had more, longer, and wider leaves thin LER hybrids but silked earlier. Both general (GCA) and specific (SCA) combining abilities were detected, but there was little evidence of interaction with environments for GCA or SCA for ALER and its components. Data indicated that selection for high ALER in a single environment should enable breeders of early maize to increase leaf area (source) without delaying maturity.
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