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

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.

Pre‐silking water deficit in maize induced kernel loss through impaired silk growth and ovary carbohydrate dynamics

“…In maize, successful development of ovaries into fully mature kernels can be disrupted in various ways, including as a result of incomplete ovary differentiation (Otegui & Andrade, 2000), late‐appearing silks or silk extrusion failure (Cárcova & Otegui, 2001; Fuad‐Hassan et al., 2008; Oury, Tardieu, et al., 2016; Rossini et al., 2020), and failure of the fertilized ovary during initial kernel development (Westgate & Boyer, 1986). Even in the absence of water deficit, disruptions of developmental events can occur, and they are rarely limited to a single reason; rather, the primary reason for unsuccessful kernel development and filling largely depends on the environmental conditions at critical stages of development (Borrás & Vitantonio‐Mazzini, 2018; Messina et al., 2019; Turc & Tardieu, 2018).…”

“…In the field, faster and more synchronous silk extrusion is beneficial for successful kernel establishment and kernel number per ear at harvest (Borrás & Vitantonio‐Mazzini, 2018; DeBruin et al., 2018; Rossini et al., 2020). Silk appearance follows a sequential order with silks in middle and basal regions of the ear emerging first while apically positioned silks lag behind by 3–4 days (Cárcova et al., 2003).…”

Diallel analysis of kernel weight and grain‐filling traits in maize grown under contrasting nitrogen supply

“…These types have been traditionally more widely used than pure dents in Argentina (Di Matteo et al., 2016). Inbreds belong to Reid Yellow Dent (B100) and Cristalino Colorado (LP2, LP561, LP611, LP662, and ZN6) heterotic groups (Eyhérabide et al., 2006; Hallauer et al., 1995) and represent variability in breeding eras, kernel type, canopy size, and grain yield traits (D'Andrea et al., 2006, 2009; Rossini et al., 2020).…”

“…By doing so, a diallel analysis will be performed on a set of hybrids derived from inbred lines of diverse genetic backgrounds (flint, semiflint, dent) under contrasting soil N environments. and Cristalino Colorado (LP2, LP561, LP611, LP662, and ZN6) heterotic groups (Eyhérabide et al, 2006;Hallauer et al, 1995) and represent variability in breeding eras, kernel type, canopy size, and grain yield traits (D'Andrea et al, 2006(D'Andrea et al, , 2009Rossini et al, 2020).…”

Combining xenia, male sterility, and synchronous pollination to improve maize grain yield and market value

“…Their MS counterparts, however, supported the additional kernels often resulting in a positive yield response. A second perhaps less critical issue is variation in ear morphology and silking dynamics that might limit the potential for adding kernels, even if the plants could support development of additional kernels (Kaeser et al., 2003; Rossini et al., 2020). Nonetheless, the results of our initial field study clearly indicate that hybrid plants can support additional kernels with much greater oil content without a yield penalty if multiple pollination effectors are applied together.…”