Leaf Expansion Rate Effects on Emergence and Juvenile Plant Growth in Early‐Maturing Maize

Good stand establishment and vigorous growth in the early spring are attributes desired in most maize ( Zea mays L.) hybrids. This field research sought to determine if selecting for higher average leaf expansion rates (ALER) in early maize could improve seedling emergence and juvenile plant growth rates. Two independent groups (GI and GII) of 16 lines were selected from S 2 lines previously rated using the formula ALER = (leaf number ✕ leaf length ✕ leaf width ✕ 0.75)/(d to pollination). Within GI and GII, eight lines with high ALER ratings (HER) were paired by source population, year of evaluation, and silking date with eight lines with low ALER ratings (LER). Sets of hybrids were produced by crossing lines from GI with lines from GII so as to represent a 2 ✕ 2 factorial arrangement of ALER hybrid types (HER ✕ HER, HER ✕ LER, LER ✕ HER, and LER ✕ LER). There were 16 hybrids (four hybrids in each of four sets) representing each hybrid type. Combining abilities of S 2 lines with differing ALER values were estimated for number of seedlings emerged, vigor ratings and leaf emergence 25 d after planting, and height of juvenile and mature plants. General combining abilities averaged across seven environments indicated that for GI, HER parents were superior to LER parents for all traits. In GII, the HER parents produced hybrids with more emerged leaves and taller juvenile plants than LER hybrids. Significant SCA appeared to be related to maternal differences for number of plants emerged, emerged leaves, vigor rating, and juvenile plant height. Results indicated that using ALER as selection criterion would produce small increases in percent emergence, early vigor ratings, and juvenile plant growth in the populations studied.