LEAF EXPANSION RATE EFFECTS ON YIELD AND YIELD COMPONENTS IN EARLY-MATURING MAIZE

Assimilate supply (source) reportedly limits grain yields of early-maturing maize (Zea mays L.) hybrids. We studied combining abilities of S2 lines with extremes in average leaf expansion rate (ALER) values to test for genetically correlated responses for grain yield, ear moisture, stalk lodging, yield components, and yield stability parameters. The S2 hybrids were selected to represent a 2 X 2 factorial arrangement of ALER types (HER = high and LER = low ALER). Two groups of lines (GI and GII) were selected from S2 lines previously rated using the formula ALER = (leaf number X length X width X 0.75)/(d to pollination). Four sets of lines with extremes for ALER ratings were paired by source population, year of evaluation, 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. Maize hybrids were grown in field experiments arranged in simple lattice designs with two replicates in seven environments. Across all environments, hybrids from HER parents yielded 8.5 and 6.9% more than LER hybrids for GI and GII, respectively. For both GI and GII, the HER hybrids produced kernel weights 0.06 g heavier than LER hybrids. The HER parents produced hybrids with ears 33 g kg-1 lower in moisture at harvest in GI. Our data support the theory that source limits yield of early maize. We suggest that selecting for HER should be a simple, effective means of increasing the source without increasing ear moisture at harvest.