Genotype and Nitrogen Effects over Maize Kernel Hardness and Endosperm Zein Profiles

Abstract

Maize (Zea mays L.) kernel hardness is of utmost importance for dry‐milling processors. Zeins, maize prolamins, are known to be key proteins affecting this trait. We investigated the response of kernel zein profiles to N fertilization in maize hybrids with contrasting kernel hardness (measured as test weight, vitreousness, kernel density, and floaters percentage). A field experiment was done during two seasons, with three N fertilization treatments and four commercial hybrids with different hardness (two flint and two dent kernel types). We also measured yield, kernel protein concentration, and zein profiles (Z2, or γ and β, and Z1, or α and δ). Flint kernel type always yielded less and showed higher kernel hardness indicators when compared with dents (P < 0.01). N fertilization helped increase yield and kernel hardness in both kernel types. Flint kernel type had consistently more Z2 than dents, while only in 1 yr Z1 was higher in flints. Dent kernel type had a Z1/Z2 ratio similar to or higher than flints. Increasing N resulted in increased concentration of both zein types, but the effect was more pronounced on Z1. Significant correlations were observed between the different zein types (Z1 and Z2) and hardness indicators and total protein concentration, but Z2 showed the highest correlations with all kernel hardness traits. Our results expand previous knowledge on genotype and N fertilization effects over zein profiles and their involvement in kernel physical characteristics relevant for dry milling.

Heat Stress during Grain Filling Modifies Kernel Protein Composition in Field‐Grown Maize

“…Glutelins constitute the protein matrix surrounding the starch granules, and major zein sub-classes (a-, b-, and g-zeins) are accumulated and packaged in protein bodies (Khoo and Wolf, 1970;Larkins and Hurkman, 1978). Among the three major sub-classes of zeins, there is evidence supporting the positive influence of g-zeins on endosperm hardness (Abdelrahman and Hoseney, 1984;Eyhérabide et al, 1996;Gerde et al, 2016;Robutti, 1992;Wu et al, 2010). Particularly in the floury (soft) fraction of the mature endosperm tissue, the protein bodies are less abundant (i.e., content of zeins is low) and smaller (i.e., there are proportionately more band g-zeins than a-zeins) than those allocated in the vitreous (hard) fraction (Chandrashekar and Mazhar, 1999;Holding, 2014).…”

Kernel Hardness‐Related Traits in Response to Heat Stress during the Grain‐Filling Period of Maize Crops

“…In addition, we clearly detected a tendency towards differential kernel hardness loss from heat stress among genotypes of contrasting endosperm texture, which had been never reported before for such a number of kernel physical traits under fieldgrowing conditions. Because of this and the significant environment × genotype interactions previously reported for numerous hardness-related traits (Eyhérabide et al, 2004;Gerde et al, 2016;Tamagno et al, 2016;Abdala et al, 2018) differences in the stability of kernel traits related to hardness between flint and dent (or semident) genotypes could be due to genetic factors other than kernel type. This genotypic tendency is consistent with the greater response in kernel physical traits to less favorable conditions for hardness expression (as regulated by year, soil N supply, and postflowering leaf area duration) of dent (or unstable flint-type expression) genotypes as compared with flint ones (Cirilo et al, 2011;Gerde et al, 2016;Tamagno et al, 2016).…”

“…2 amplified such effects up to levels higher than those promoted by low soil water or nutrient availabilities and high stand densities (Shumway et al, 1992;Gerde et al, 2016;Tamagno et al, 2016). In this regard, the higher levels of solar radiation during the effective grain-filling period in Exp.…”

“…Gerde et al (2016) stated that band g-zeins and, to a lesser extent, aand d-zeins were positively related with kernel hardness attributes when dealing with environmental (years and soil N supply) and genetic (specific genotypes within kernel type) effects. According to several studies (Mestres and Matencio, 1996, and references cited therein; Gerde et al, 2016), genotypic differences in maize hardness variation would be accounted for by the amount of specific g-zein components. These authors also reported that a-zein content exerts influence on only certain kernel hardness-related traits, suggesting that the biochemical basis might vary between kernel hardness-related traits.…”

“…The incidence of such abiotic constraint, which is expected to become more frequent with global warming (Eyshi Rezaei et al, 2015), can provoke large grain yield losses (i.e., heat stress; Wahid et al, 2007) through kernel abortion (Rattalino Edreira et al, 2011) and/or cessation of kernel growth Rattalino Edreira et al, 2014). Given the positive influence of protein concentration and g-zeins on kernel hardness and its related traits (Fox and Manley, 2009;Gerde et al, 2016, and references cited therein), heat stress could lead to lighter but harder kernels. Given the positive influence of protein concentration and g-zeins on kernel hardness and its related traits (Fox and Manley, 2009;Gerde et al, 2016, and references cited therein), heat stress could lead to lighter but harder kernels.…”