Genetic Factors Underlying Dry‐Milling Efficiency and Flaking‐Grit Yield Examined in US Maize Germplasm

Abstract

A small but important proportion of US maize (Zea mays L.) grain is channeled to create breakfast cereals and other food products; yet, little focus has been devoted to genetic improvement of corn hybrids to meet needs of dry millers and other end users in the cereal pipeline. This study was designed to evaluate a broad range of US maize germplasm for key dry‐milling traits: dry‐milling efficiency (DME), the proportion of flaking grits produced from dry‐milled maize grain, and flaking‐grit yield (FGY), the amount of flaking grits produced per unit land. Genetic parameters for DME and FGY were characterized based on grain produced over 3 yr, and the associations between dry‐milling, agronomic, ear, and kernel traits were assessed. Means for DME among experimental hybrids ranged from 24.0 to 36.0%. The DME was negatively correlated with grain yield and positively correlated with test weight; associations with other ear and kernel traits were weak despite being statistically significant in some cases. The DME is moderately heritable (h2 = 0.53) and controlled largely by additive gene action. A moderate amount (31%) of the variation in FGY was explained by multiple linear regression of grain yield and simple physical kernel properties: test weight, kernel thickness, and 100‐kernel volume. Genetic variation for DME in US maize germplasm was demonstrated, which could be exploited to develop new maize hybrids with improved DME and, ultimately, FGY. However, more work is needed to develop indirect selection approaches to predict DME and FGY at or before harvest.

Incomplete dominance of deleterious alleles contributes substantially to trait variation and heterosis in maize

“…We found the cumulative proportion of dominance variance explained by GERP-SNPs was higher for traits showing high heterosis (Spearman correlation P value < 0.01, r = 0.9), from ≈ 0 for flowering time traits to as much as 24% for grain yield (S6 Fig). Distributions of per-SNP dominance (see Methods) across traits were consistent with the cumulative partitioning of variance components (Fig 2b) and matched well with expectations from previous studies showing a predominantly additive basis for flowering time [54] and plant height [55] but meaningful contributions of dominance to test weight and grain yield [28, 30]. Although our diallel population is relatively small, our estimated values explain as much (for traits with low dominance variance like flowering time) or more variance (for traits with substantial dominance variance like grain yield) than sets of data with randomly shuffled values of dominance (n = 10 randomizations of k per trait; S7 Fig).…”

Incomplete Dominance of Deleterious Alleles Contributes Substantially to Trait Variation and Heterosis in Maize

“…GERP-SNPs had larger average effects and explained more phenotypic variance than the same number of randomly sampled SNPs (including SNPs with GERP score < = 0) matched for allele frequency and recombination (Fig 2a). We found the cumulative proportion of dominance variance explained by GERP-SNPs was higher for traits showing high heterosis (Spearman correlation P value < 0.01, r = 0.9), from % 0 for flowering time traits to as much as 24% for grain yield (S6 Fig). Distributions of per-SNP dominance k ¼ d a (see Methods) across traits were consistent with the cumulative partitioning of variance components (Fig 2b) and matched well with expectations from previous studies showing a predominantly additive basis for flowering time [54] and plant height [55] but meaningful contributions of dominance to test weight and grain yield [28,30]. Although our diallel population is relatively small, our estimated values explain as much (for traits with low dominance variance like flowering time) or more variance (for traits with substantial dominance variance like grain yield) than sets of data with randomly shuffled values of dominance (n = 10 randomizations of k per trait; S7 Fig).…”

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

“…Kernel size, which is positively associated to hardness when addressing different crop growing conditions for a given genotype (Cirilo to enhance the separation among the pericarp, the germ, and the endosperm tissues and, thereby, to obtain flaking grits from the latter tissue (i.e., endosperm particles larger than 4 mm and smaller than 5.66 mm; Eckhoff and Paulsen, 1996;Macke et al, 2016). Kernel size, which is positively associated to hardness when addressing different crop growing conditions for a given genotype (Cirilo to enhance the separation among the pericarp, the germ, and the endosperm tissues and, thereby, to obtain flaking grits from the latter tissue (i.e., endosperm particles larger than 4 mm and smaller than 5.66 mm; Eckhoff and Paulsen, 1996;Macke et al, 2016).…”

“…Kernel samples were oven dried at 65°C during 48 h to determine plant grain yield and kernel number per plant. Kernel size, which is positively associated to hardness when addressing different crop growing conditions for a given genotype (Cirilo to enhance the separation among the pericarp, the germ, and the endosperm tissues and, thereby, to obtain flaking grits from the latter tissue (i.e., endosperm particles larger than 4 mm and smaller than 5.66 mm; Eckhoff and Paulsen, 1996;Macke et al, 2016). Conditioned kernel samples were fed into an experimental miller with a sealed chamber with adjustable stationary cutting edges and a rotating head with four cutting edges that revolve at high speed.…”