Heterosis and parent-progeny relationships for silk extrusion dynamics and kernel number determination in maize: Nitrogen effects

Maize (Zea mays L.) ear-related traits conducive to final kernel number per plant (KNP) are currently considered key determinants of kernel set under abiotic stress. Understanding of the variation between parental inbred lines and their hybrids is limited. The objective of this work was to analyze the genotypic variation between a set of inbred lines and some of their derived hybrids for (a) total number of spikelets per ear, (b) silk extrusion dynamics, (c) KNP, and (d) sources of loss in KNP (i.e., silk and kernel abortions) under high and limited N supply. In inbreds, variations in KNP were strongly explained by variations in silk extrusion rate (SER) and silk abortion. In contrast, hybrid KNP was explained by the number of spikelet per ear, exposed silks on Day 5 (ESD5), and extruded silks (TES), as well as silk extrusion per unit area (ESMAX). Heterosis across N levels was high for KNP, ESMAX, SER, kernel abortion, and ESD5. Strong parent-progeny relationships (r >= .69, P < .01) were computed for reproductive morphology traits (TES, total spikelets) at both N levels, whereas (a) KNP, sources of loss, and ESMAX were highly heritable exclusively under high N supply, and (b) ESD5 was a good predictor of hybrids KNP only at low N supply. Based on its high heterosis across environments and good parent-progeny relationship for KNP under N deficiency, ESD5 quantification should be part of breeding programs aimed to low-N environments, depending upon the development of image-based plant and crop phenotyping.