Kernel Weight Determination in Maize Inbred Lines and Derived Hybrids.

Maize (Zea mays L.) kernel weight (KW) is determined by different combinations of kernel growth rate (KGR) and grain-filling duration (GFD), which vary independently. All three traits have a large phenotypic plasticity, and are affected by genotype and environment effects as well as by their interaction. However, knowledge on the genotypic variation and genetic control of mentioned traits is limited, and we studied them by means of a field experiment that included 4 parental inbred lines (B100, LP2, LP662, ZN6) and all possible F1 hybrids in a complete diallel mating design, under contrasting N conditions, during 2013-2014 in Argentina. We found (i) that the main determinant of KW was KGR (r²=0.42) in hybrids and GFD (r²=0.53) in inbreds, (ii) a trade-off effect between KGR and GFD, except for the hybrid of highest KW (LP2×LP662), (iii) that differences in KW between hybrids and inbreds were due to GFD, (iv) a significant heterosis (P<0.01) only for KW (14.96%) and GFD (6.10%), (v) high heritability values for KW (0.84), KGR (0.69) and GFD (0.74), (vi) a significant additive genetic control for KGR (p<0.05) and GFD (p<0.01), but not for KW (controlled mainly by non-additive genetic effects), and (vii) that the cross between a high-KGR inbred and a high-GFD (both with contrasting KW) produced the hybrid with largest KW, in accordance with non-additive effects on KW. Therefore, selection based on the physiological determinants of KW would be more efficient than selection based exclusively on KW.