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Maize (Zea mays L.) grown in the US Midwest contains only a small fraction of the genetic diversity present in the species. Maize populations from other parts of the world may contain genetic variation that could be used to improve or increase the diversity of US germplasm. This study was conducted to assess the performance and phenotypic stability of hybrids containing diverse exotic introgressions across North American environments. Doubled haploid (DH) lines were created by the Germplasm Enhancement of Maize project from backcross 1 families that used 27 open‐pollinated populations from Latin America as donor parents and PHZ51, a non‐Stiff Stalk inbred developed in Iowa, as the recurrent parent. DH lines were testcrossed with LH195, a Stiff Stalk inbred developed in Iowa, and hybrid field trials were performed at 24 environments in the United States and Canada. Experimental hybrids had variable flowering time, plant and ear height, and test weight, but none had significantly greater yield than the PHZ51 × LH195 hybrid. The slopes of linear reaction norm models were significantly lower for the experimental hybrids than the US‐adapted reference hybrids for three traits: yield, growing degree units (GDU) to anthesis, and GDU to silking. The results suggest that unfavorable alleles and phenotypic stability should be considered when exotic open‐pollinated populations are used in US maize breeding. Core Ideas: Open‐pollinated maize populations are diverse and contain haplotypes that are rare or absent in US germplasm.Hybrids with exotic introgressions had variation in flowering time, plant height, and ear height.None of the hybrids with introgressions had significantly greater yield than the recurrent parent hybrid.Exotic‐derived hybrids and US hybrids had significantly different phenotypic stability for some traits. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is one of the most consumed grains in the world. Within the context of continuous climate change and the reduced availability of arable land, it is urgent to breed new maize varieties and screen for the desired traits, e.g., high yield and strong stress tolerance. Traditional phenotyping methods relying on manual assessment are time-consuming and prone to human errors. Recently, the application of uncrewed aerial vehicles (UAVs) has gained increasing attention in plant phenotyping due to their efficiency in data collection. Moreover, hyperspectral sensors integrated with UAVs can offer data streams with high spectral and spatial resolutions, which are valuable for estimating plant traits. In this study, we collected UAV hyperspectral imagery over a maize breeding field biweekly across the growing season, resulting in 11 data collections in total. Multiple machine learning models were developed to estimate the grain yield and flowering time of the maize breeding lines using the hyperspectral imagery. The performance of the machine learning models and the efficacy of different hyperspectral features were evaluated. The results showed that the models with the multi-temporal imagery outperformed those with imagery from single data collections, and the ridge regression using the full band reflectance achieved the best estimation accuracies, with the correlation coefficients (r) between the estimates and ground truth of 0.54 for grain yield, 0.91 for days to silking, and 0.92 for days to anthesis. In addition, we assessed the estimation performance with data acquired at different growth stages to identify the good periods for the UAV survey. The best estimation results were achieved using the data collected around the tasseling stage (VT) for the grain yield estimation and around the reproductive stages (R1 or R4) for the flowering time estimation. Our results showed that the robust phenotyping framework proposed in this study has great potential to help breeders efficiently estimate key agronomic traits at early growth stages. [ABSTRACT FROM AUTHOR]

New maize (Zea mays L.) inbred lines are commonly evaluated based on the performance of their progeny when crossed to a single tester line from a different heterotic group (testcross), making tester choice critical. An alternative progeny test is pairing new lines between heterotic groups such that every parent is observed in one hybrid combination. This approach requires half the number of hybrids to test but the general combining ability (GCA) of each parent cannot be estimated. Genomic information can be used to partition parental GCA, while potentially enabling the prediction of dominance deviations. We evaluated doubled haploid lines extracted from two six‐parent synthetic populations from the Iodent (IO) and Stiff Stalk (SS) heterotic groups using either single crosses from random pairs of inbreds or testcrosses. Hybrids were evaluated for yield and agronomic traits in 2014 and 2015 in south‐central Wisconsin. The experiment was conducted using a randomized complete block design with each population type grown in two replicates within two environments. Coincidence of selection of the 25 top performing lines based on testcross yield and single‐cross hybrid yield was 48% for the SS and 11% for the IO doubled haploid lines, increasing to 56% for the SS and 56% for the IO with genomic prediction based on an additive genomic model. Partitioning dominance deviations with the model increased coincidence to 62% for the SS population. Genomic estimates of grain yield GCA in the single‐cross hybrids were significantly more correlated than phenotypic GCA to testcross values for the IO lines, but not SS. Natural and orthogonal interaction estimates of dominance variation were insignificant for all traits, indicating that the inability to partition dominance based on testcross performance should not be a major limitation to identification of high‐performing hybrids. Genomic information improves the prospects of using single‐cross hybrids made from random pairs of new inbreds as an efficient progeny test by allowing the recovery of parental GCA information. Core Ideas: Testcross analysis may preclude detection of heterotic hybrids of two new inbred lines.We tested random crosses of new inbreds coupled with genomic selection as an approach to hybrid selection.Genomic selection of inbreds from randomly paired single‐crosses was effective.Logistic issues in seed production may preclude the value of hybrid selection using pairs. [ABSTRACT FROM AUTHOR]

SUMMARY: Single‐parent expression (SPE) is defined as gene expression in only one of the two parents. SPE can arise from differential expression between parental alleles, termed non‐presence/absence (non‐PAV) SPE, or from the physical absence of a gene in one parent, termed PAV SPE. We used transcriptome data of diverse Zea mays (maize) inbreds and hybrids, including 401 samples from five different tissues, to test for differences between these types of SPE genes. Although commonly observed, SPE is highly genotype and tissue specific. A positive correlation was observed between the genetic distance of the two inbred parents and the number of SPE genes identified. Regulatory analysis showed that PAV SPE and non‐PAV SPE genes are mainly regulated by cis effects, with a small fraction under trans regulation. Polymorphic transposable element insertions in promoter sequences contributed to the high level of cis regulation for PAV SPE and non‐PAV SPE genes. PAV SPE genes were more frequently expressed in hybrids than non‐PAV SPE genes. The expression of parentally silent alleles in hybrids of non‐PAV SPE genes was relatively rare but occurred in most hybrids. Non‐PAV SPE genes with expression of the silent allele in hybrids are more likely to exhibit above high parent expression level than hybrids that do not express the silent allele, leading to non‐additive expression. This study provides a comprehensive understanding of the nature of non‐PAV SPE and PAV SPE genes and their roles in gene expression complementation in maize hybrids. Significance Statement: Single‐parent expression (SPE) is defined as gene expression in only one of the two parents. This expression state can arise from differential expression between parental alleles, termed non‐presence/absence (non‐PAV) SPE, or the physical absence of a gene in one parent, termed PAV SPE. This study provides a comprehensive understanding of the nature of non‐PAV SPE and PAV SPE genes and their roles in gene expression complementation in maize hybrids. [ABSTRACT FROM AUTHOR]

Objectives: Advanced tools and resources are needed to efficiently and sustainably produce food for an increasing world population in the context of variable environmental conditions. The maize genomes to fields (G2F) initiative is a multi-institutional initiative effort that seeks to approach this challenge by developing a flexible and distributed infrastructure addressing emerging problems. G2F has generated large-scale phenotypic, genotypic, and environmental datasets using publicly available inbred lines and hybrids evaluated through a network of collaborators that are part of the G2F's genotype-by-environment (G × E) project. This report covers the public release of datasets for 2014–2017. Data description: Datasets include inbred genotypic information; phenotypic, climatic, and soil measurements and metadata information for each testing location across years. For a subset of inbreds in 2014 and 2015, yield component phenotypes were quantified by image analysis. Data released are accompanied by README descriptions. For genotypic and phenotypic data, both raw data and a version without outliers are reported. For climatic data, a version calibrated to the nearest airport weather station and a version without outliers are reported. The 2014 and 2015 datasets are updated versions from the previously released files [1] while 2016 and 2017 datasets are newly available to the public. [ABSTRACT FROM AUTHOR]

Plant breeders face the challenge of genotype × environment interaction (G × E) in comprehensively breeding for expanded geographic regions. An improved understanding of G × E sensitivity of traits and the environmental features that effectively discriminate among genotypes will enable more efficient breeding efforts. In this study of 31 maize (Zea mays L.) inbreds grown in 36 environments that are part of the Genomes to Fields Initiative, we measured 14 traits, including flowering date, height, and yield components (i.e., ear and kernel dimensions) to (i) identify traits that are the most sensitive indicators of G × E; (ii) determine how geographic location and weather factors influence environments' discriminability of inbreds; and (iii) detect patterns of stability in better and worse discriminating environments. Genotype × environment interaction explained between 9.0–20.4% of the phenotypic variance with greater effects in the yield‐component traits. Discriminability of environments varied by trait. Midwest locations (where 26 of the 31 inbreds were developed) were among the most discriminating environments for more traits, while environments in the West and East tended to be less discriminating. Weather factors during silking were significantly different between the most and least discriminating environments more often than average weather across the season or during the period from planting to silking. Stability of genotypes varied by trait, and performance was usually not correlated with stability. The dissection of complex traits, such as yield into component traits, appears to be a useful approach to understand how environmental factors differentially affect phenotype. [ABSTRACT FROM AUTHOR]

Publicly available maize (Zea mays L.) inbred lines with expired Plant Variety Protection certificates (ex‐PVP) constitute the elite germplasm used in hybrids grown by North American farmers during the past half century. A set of 329 ex‐PVP inbreds and eight public reference inbreds was evaluated for genetic diversity using molecular marker and pedigree‐based relationships. The majority of inbreds originated from Dekalb Genetics Corporation, Holden's Foundation Seed, Pioneer Hi‐Bred International, and Syngenta via Novartis and Northrup King. Flowering ranged from 968–1806 growing degree days to anthesis, supporting that these inbreds represent adaptation across the range of North American production environments. Admixture analysis supported eight subgroups (B14, B37, B73, Oh43, Iodent, Iodent‐Lancaster, Lancaster, and Flint), reflecting heterotic patterns and company of origin. Five diallel‐cross experiments identified primary yield heterotic patterns within early‐, intermediate‐, and late‐maturity groups. Parental pedigree information was compiled for 2392 Plant Variety Protection and/or utility patented inbreds through 2017, allowing for multigenerational analysis of progenitors and the eight heterotic subgroups across current proprietary breeding programs. Key progenitors were identified for recently merged companies, Bayer Crop Science and Corteva Agriscience. The results of this study strengthen the value of the ex‐PVP inbreds as a source of elite and relevant germplasm for breeders and researchers to exploit. This study provides information that will be logistically useful to researchers who use ex‐PVP inbreds and adds to our understanding of heterotic grouping within North American proprietary germplasm. [ABSTRACT FROM AUTHOR]

A correction for the article "Relative utility of agronomic, phenological, and morphological traits for assessing genotype-by-environment interaction in maize inbreds" is presented, which is published in the previous issue of the periodical.

Remarkable productivity has been achieved in crop species through artificial selection and adaptation to modern agronomic practices. Whether intensive selection has changed the ability of improved cultivars to maintain high productivity across variable environments is unknown. Understanding the genetic control of phenotypic plasticity and genotype by environment (G × E) interaction will enhance crop performance predictions across diverse environments. Here we use data generated from the Genomes to Fields (G2F) Maize G × E project to assess the effect of selection on G × E variation and characterize polymorphisms associated with plasticity. Genomic regions putatively selected during modern temperate maize breeding explain less variability for yield G × E than unselected regions, indicating that improvement by breeding may have reduced G × E of modern temperate cultivars. Trends in genomic position of variants associated with stability reveal fewer genic associations and enrichment of variants 0-5000 base pairs upstream of genes, hypothetically due to control of plasticity by short-range regulatory elements. [ABSTRACT FROM AUTHOR]

Developing biofortified maize (Zea mays L.) cultivars is a viable approach to combating the widespread problem of vitamin A deficiency among people for whom maize is a staple food. To enhance CIMMYT's provitamin A maize breeding efforts, this study: (i) evaluated whether separation of experimental maize lines into groups based on maximizing their molecular-markerbased genetic distances (GD) resulted in heterosis for among-group crosses, (ii) assessed genetic effects (general and specific combining ability, GCA and SCA) for grain yield and provitamin A concentrations in hybrids among 21 inbred lines representing the three proposed groups, and (iii) assessed the association between grain yield and provitamin A concentrations. The lines were crossed following a partial diallel design resulting in 156 hybrids that were evaluated at four environments with two replications of onerow plots. The first plant in each plot was selfpollinated to produce grain for provitamin A analysis. Significant but small yield advantage of among- versus within-group crosses (0.47 Mg ha-1, P < 0.05) suggested that the groups identified by maximizing GD could be a practical starting point for further breeding work to develop useful heterotic groups. Furthermore, the GDproposed heterotic groups were improved by later revising some line assignments to groups using estimates of SCA effects. General combining ability effects were significant (P < 0.01) for all traits, whereas SCA effects were weak (P < 0.05) or not significant for provitamin A carotenoid concentrations, indicating that these were controlled primarily by additive gene action. Grain yield was not significantly correlated with provitamin A concentration, indicating that both traits could be improved simultaneously. [ABSTRACT FROM AUTHOR]

Association analysis to identify genes and alleles underlying quantitative genetic variation is growing in value as the density of, genotypic data increases. Association panels are often chosen to maximize molecular and phenotypic diversity, but traits measured at harvest require restricted phenology to obtain data on plants that mature within a comparable interval. The objective of this study was to characterize a set of inbred lines that will mature reliably in the upper midwestern United States for the purpose of assessing traits relevant to grain and stover yield as well as stover quality. A total of 1411 lines from the North Central Regional Plant Introduction Station, our program, and contributed by collaborators were grown in observation plots. A set of 627 lines were chosen based on flowering within the desired interval, production of viable seed, agronomic suitability, uniformity, and pedigree information. Flowering time ranged from 944 to 1645 growing degree days (GDD). Genotypic data for the 627 lines was obtained using a 1536 Iflumina GoldenGate assay. The panel offers deep replication of most Midwest dent alleles. There is a lesser representation of tropical alleles relative to other association panels but includes some Germplasm Enhancement of Maize (GEM)-derived lines and early flowering lines of tropical origin. The information described in this manuscript is anticipated to facilitate the use of this material for association genetic studies. [ABSTRACT FROM AUTHOR]

Quantifies the difference among maize inbred lines for growth at low soil phosphorus levels and response to mycorrhizal fungi. Quantitative trait loci controlling different traits; Correlation between the percentage of root colonization and mycorrhizal responsiveness; Substantial variation among maize lines for growth at low phosphorus levels.