No abstract

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 imagebased plant and crop phenotyping.Abbreviations: ASI, anthesis-silking interval; AUC, area under the curve; ESD5, exposed silks per ear on Day 5; ESMAX, maximum number of exposed silks per square meter; GG, genotypic group; INTA, National Institute of Agricultural Technology; KNP, kernel number per plant; PC, principal component; SER, silk extrusion rate; TES, total extruded silks; TTANT, thermal time to anthesis; TTAS, thermal time after the start of silking; TTESMAX, thermal time after silking when the maximum number of exposed silks per square meter is reached; TTSILK, thermal time to silking.

Maize (Zea mays L.) grain yield is assumed to be source limited during the flowering period but sink limited during grain growth; however, environmental restrictions during active grain filling may strongly affect final kernel weight (KW). In this study, we evaluated the effect of natural changes in photothermal conditions during lag phase (LP) and effective grain‐filling period (EGFP) on KW, its physiological determinants, and the post‐flowering source–sink relationships of flint and semident germplasm. F1 hybrids of flint × flint and dent × flint background were tested during four seasons (Y1, Y2, Y3, and Y4). Across years, the highest KW (286 mg) was obtained under the maximum photothermal quotients during LP (PTQLP = 1.18 MJ m−2 °C−1) and EGFP (PTQEGFP = 1.07 MJ m−2 °C−1) of Y2, whereas the smallest KW (252 mg) and source–sink ratio during grain filling was obtained under the lowest PTQEGFP (.79 MJ m−2 °C−1) of Y3. Supra‐optimum temperatures during LP of Y3 negatively affected potential KW determination, and hence kernel growth rate (P < .001) as a result of reduced assimilate availability per kernel. Hybrids dent × flint exhibited higher grain yield, kernel number, and plant growth around flowering than flint × flint throughout evaluated seasons but had reduced source–sink relationship during grain filling (P < .05) and increased KW sensitivity (P < .001) to changes in the photothermal conditions. Results emphasized the importance of the photothermal environment during grain filling on KW determination (particularly for seasons with great photothermal imbalance between filling subphases) as well as the dependency of KW responses on the genetic background.