Maize Accessions Research Articles

Special issue in honour of Prof. Reto J. Strasser - Comparative analysis of drought stress response of maize genotypes using chlorophyll fluorescence measurements and leaf relative water content

The initial photochemical quantum efficiency of photosystem II (Fv/Fm) and performance index (PI), describing the ability of the photosynthetic apparatus to collect light energy, have been used to screen tolerance to drought stress by ten maize accessions, monitored by leaf relative water content (RWC) and soil water content (SWC). The Fv/Fm, PI, and RWC values were significantly reduced in drought-stressed plants. The analysis of chlorophyll a fluorescence induction rise from the basic dark-adapted fluorescence yield to the maximum (OJIP transient), distinguished accession Zea 1006 from Libya and Zea 612 from Italy, as the most tolerant and the least tolerant genotypes. The maize genotypes were classified using the Principal Component Analysis (PCA) and clustering methods, based on Fv/Fm and PI values, leaf RWC and SWC. Genotypes from Egypt and Libya were differentiated from genotypes from Europe, Russia and the USA.

A large-scale screening of maize germplasm for resistance to multiple diseases in multi-plot demonstration for several years under natural condition

<p indent=0mm>Disease is a major factor affecting maize production. The utilization of resistant cultivars is the most economical, safe, and effective method for controlling maize diseases. This research was finally conducted using 2000 maize germplasm accessions with extensive sources and rich genetic background to identify and evaluate the resistance to multiple diseases in multi-plot demonstration for several years under natural condition during 2016–2019. Nine diseases, including southern corn leaf blight, stalk rot, common smut, <italic>Curvularia</italic> leaf spot, southern rust, maize rough dwarf, northern corn leaf blight, gray leaf spot and head smut were investigated and evaluated in non-inoculated fields. The experimental data at 10 different sites from 2016 to 2019 showed that resistance identification under natural conditions was sensitive to environmental factors, with distinct differences among years and regions. The incidence of southern corn leaf blight was severe at multiple sites over these years and 11 maize accessions with stable resistance were screened out. Stalk rot, northern corn leaf blight, and gray leaf spot were relatively serious at several sites in four years, and 440, 356, and 423 resistant germplasm were screened out from 2000 accessions, respectively. These integrated data had considerable reference values. Curvularia leaf spot, common smut, and maize rough dwarf occurred heavily at only one plot while southern rust and head smut were not serious at all experimental sites, which should be studied further more. All in all, some maize germplasm resources with stable resistance to diverse diseases under different environments were screened out, such as JN15, 953, Shen 977, 68122, K21, SC24-1, 17MC7211, 17MC7223, Zheng 591, 161191, and so on. These results provide a significant reference for utilization and selection of germplasm for further precise inoculated identification.

Assessing the Potential of Extra-Early Maturing Landraces for Improving Tolerance to Drought, Heat, and Both Combined Stresses in Maize

Maize landrace accessions constitute an invaluable gene pool of unexplored alleles that can be harnessed to mitigate the challenges of the narrowing genetic base, declined genetic gains, and reduced resilience to abiotic stress in modern varieties developed from repeated recycling of few superior breeding lines. The objective of this study was to identify extra-early maize landraces that express tolerance to drought and/or heat stress and maintain high grain yield (GY) with other desirable agronomic/morpho-physiological traits. Field experiments were carried out over two years on 66 extra-early maturing maize landraces and six drought and/or heat-tolerant populations under drought stress (DS), heat stress (HS), combined both stresses (DSHS), and non-stress (NS) conditions as a control. Wide variations were observed across the accessions for measured traits under each stress, demonstrating the existence of substantial natural variation for tolerance to the abiotic stresses in the maize accessions. Performance under DS was predictive of yield potential under DSHS, but tolerance to HS was independent of tolerance to DS and DSHS. The accessions displayed greater tolerance to HS (23% yield loss) relative to DS (49% yield loss) and DSHS (yield loss = 58%). Accessions TZm-1162, TZm-1167, TZm-1472, and TZm-1508 showed particularly good adaptation to the three stresses. These landrace accessions should be further explored to identify the genes underlying their high tolerance and they could be exploited in maize breeding as a resource for broadening the genetic base and increasing the abiotic stress resilience of elite maize varieties.

Transcriptome and GWAS analyses reveal candidate gene for seminal root length of maize seedlings under drought stress

Water deficits are a major constraint on maize growth and yield, and deep roots are one of the major mechanisms of drought tolerance. In this study, four root and shoot traits were evaluated within an association panel consisting of 209 diverse maize accessions under well-watered (WW) and water-stressed (WS) conditions. A significant positive correlation was observed between seminal root length (SRL) under WS treatment and the drought tolerance index (DI) of maize seedlings. The transcriptome profiles of maize seminal roots were compared between four drought-tolerant lines and four drought-sensitive lines under both water conditions to identify genes associated with the drought stress response. After drought stress, 343 and 177 common differentially expressed genes (DEGs) were identified in the drought-tolerant group and drought-sensitive group, respectively. In parallel, a coexpression network underlying SRL was constructed on the basis of transcriptome data, and 10 hub genes involved in two significant associated modules were identified. Additionally, a genome-wide association study (GWAS) of the SRL revealed 62 loci for the two water treatments. By integrating the results of the GWAS, the common DEGs and the coexpression network analysis, 7 promising candidate genes were prioritized for further research. Together, our results provide a foundation for the enhanced understanding of seminal root changes in response to drought stress in maize.

VALIDACIÓN EMPÍRICA DE LA TEORÍA MULTICÉNTRICA DEL ORIGEN Y DIVERSIDAD DEL MAÍZ EN MÉXICO

Mesoamerica is considered as the center of origin and diversity of maize (Zea mays L.). The multicentric theory on the origin and diversity of maize defines five centers of origin-domestication, from which four macro regions or primary centers of diversification of this cereal were conformed, from which the different races and the concentration of diversity emerged. A center of genetic diversity is defined as the geographical area where there is morphological, genetic diversity, or both, for a certain species, characterized by harboring populations of wild relatives and constituting a genetic reserve. The objective of this study was to empirically validate the geographic regions of Mexico that conform to the definition of a center of genetic diversity for maize. Spatial analysis was used to examine the diversity and distribution of 24,126 accessions of native maize and 1,106 records of wild relatives (Teosinte: 692 and Tripsacum: 414) collected during the period 1926 2014, available at germplasm banks and herbaria of national and international agricultural research and education institutions located in Mexico and, through the use of geographic information systems and modeling. In accordance with the criteria and definitions considered in the multicentric theory on maize origin and diversity, 19 geographic regions were empirically defined and validated to be considered as centers of genetic diversity of maize native to Mexico.

Assessment of Genetic Diversity for Drought, Heat and Combined Drought and Heat Stress Tolerance in Early Maturing Maize Landraces.

Climate change is expected to aggravate the effects of drought, heat and combined drought and heat stresses. An important step in developing ‘climate smart’ maize varieties is to identify germplasm with good levels of tolerance to the abiotic stresses. The primary objective of this study was to identify landraces with combined high yield potential and desirable secondary traits under drought, heat and combined drought and heat stresses. Thirty-three landraces from Burkina Faso (6), Ghana (6) and Togo (21), and three drought-tolerant populations/varieties from the Maize Improvement Program at the International Institute of Tropical Agriculture were evaluated under three conditions, namely managed drought stress, heat stress and combined drought and heat stress, with optimal growing conditions as control, for two years. The phenotypic and genetic correlations between grain yield of the different treatments were very weak, suggesting the presence of independent genetic control of yield to these stresses. However, grain yield under heat and combined drought and heat stresses were highly and positively correlated, indicating that heat-tolerant genotypes would most likely tolerate combined drought and stress. Yield reduction averaged 46% under managed drought stress, 55% under heat stress, and 66% under combined drought and heat stress, which reflected hypo-additive effect of drought and heat stress on grain yield of the maize accessions. Accession GH-3505 was highly tolerant to drought, while GH-4859 and TZm-1353 were tolerant to the three stresses. These landrace accessions can be invaluable sources of genes/alleles for breeding for adaptation of maize to climate change.

INVINH1 Gene Alleliс Polymorphism in Maize Accessions from VIR Collection

The sequences of the apoplastic invertase inhibitor gene INVINH1 were identified in 71 maize accessions from the collection of the Vavilov All-Russian Institute of Plant Genetic Resources (VIR). In total, 35 INVINH1 allelic variants were found. In 21 maize accessions, at position –95 from the start codon, INVINH1 contained an extended insertion (143, 190, 192, or 210 bp). In INVINH1 proteins, 21 amino acid substitutions were identified, six of which (A49V, A49G, A65P, S97I, C99R, and D108Y), predicted to be radical, were localized in the PMEI functional domain.

Identifying loci with breeding potential across temperate and tropical adaptation via EigenGWAS and EnvGWAS.

Understanding the genomic basis of adaptation in maize is important for gene discovery and the improvement of breeding germplasm, but much remains a mystery in spite of significant population genetics and archaeological research. Identifying the signals underpinning adaptation are challenging as adaptation often coincided with genetic drift, and the base genomic diversity of the species in massive. In this study, tGBS technology was used to genotype 1,143 diverse maize accessions including landraces collected from 20 countries and elite breeding lines of tropical lowland, highland, subtropical/midaltitude and temperate ecological zones. Based on 355,442 high‐quality single nucleotide polymorphisms, 13 genomic regions were detected as being under selection using the bottom‐up searching strategy, EigenGWAS. Of the 13 selection regions, 10 were first reported, two were associated with environmental parameters via EnvGWAS, and 146 genes were enriched. Combining large‐scale genomic and ecological data in this diverse maize panel, our study supports a polygenic adaptation model of maize and offers a framework to enhance our understanding of both the mechanistic basis and the evolutionary consequences of maize domestication and adaptation. The regions identified here are promising candidates for further, targeted exploration to identify beneficial alleles and haplotypes for deployment in maize breeding.

Allelic polymorphism of &lt;i&gt; crtRB1 &lt;/i&gt; and &lt;i&gt; LcyE &lt;/i&gt; genes related to the β-carotene content in Vietnamese traditional maize accessions,

Maize is the third most important food crop after wheat and rice. Maize is used as food for more than a billion people around the world and is used as animal feed, especially, poultry. The concentration of carotenoids, especially, β-carotene in maize grains, is very low. Therefore, the study of increasing the amount of provitamin A carotenoids including β-carotene is important. In maize, different alleles of crtRB1 and LcyE genes have a significant effect on β-carotene content. In this paper, we present the results of the study of allele polymorphism of these two genes related to the provitamin A carotenoid content in some traditional maize accessions collected from several regions in North and Central Highlands of Vietnam. The results showed that there were polymorphisms at the 3’ and 5’ ends of the crtRB1 and LcyE genes. Among 22 maize accessions, the proportion of favorable alleles at the 3’ end of crtRB1 gene was relatively high (5/22 = 22.73%). Similar results were obtained for alleles at 3’ end of the LcyE gene. Especially, there is an accession (Northern white gold maize) that carries favorable alleles at the 3’ ends of both crtRB1 and LcyE genes. While all investigated maize accessions did not carry favorable alleles at the 5’ end of both crtRB1 and LcyE genes. The identification of traditional maize accessions that carry favorable alleles for increasing b-carotene content opens up potential to exploit indigenous genetic resources for genetic research as well as to develop maize varieties with high β- carotene content.

Allelic polymorphism of &lt;i&gt; crtRB1 &lt;/i&gt; and &lt;i&gt; LcyE &lt;/i&gt; genes related to the β-carotene content in Vietnamese traditional maize accessions,

Maize is the third most important food crop after wheat and rice. Maize is used as food for more than a billion people around the world and is used as animal feed, especially, poultry. The concentration of carotenoids, especially, β-carotene in maize grains, is very low. Therefore, the study of increasing the amount of provitamin A carotenoids including β-carotene is important. In maize, different alleles of crtRB1 and LcyE genes have a significant effect on β-carotene content. In this paper, we present the results of the study of allele polymorphism of these two genes related to the provitamin A carotenoid content in some traditional maize accessions collected from several regions in North and Central Highlands of Vietnam. The results showed that there were polymorphisms at the 3’ and 5’ ends of the crtRB1 and LcyE genes. Among 22 maize accessions, the proportion of favorable alleles at the 3’ end of crtRB1 gene was relatively high (5/22 = 22.73%). Similar results were obtained for alleles at 3’ end of the LcyE gene. Especially, there is an accession (Northern white gold maize) that carries favorable alleles at the 3’ ends of both crtRB1 and LcyE genes. While all investigated maize accessions did not carry favorable alleles at the 5’ end of both crtRB1 and LcyE genes. The identification of traditional maize accessions that carry favorable alleles for increasing b-carotene content opens up potential to exploit indigenous genetic resources for genetic research as well as to develop maize varieties with high β- carotene content.

Evaluation of Maize Varieties for Grain Yield under Water-restricted Conditions

The study sought to evaluate maize germplasm accessions from the Ifes Germplasm Bank (Ifes BAG) to identify promising lines for breeding programs to increase yield under water-restricted conditions. A competition trial was carried in two contrasting environments in the state of Espírito Santo, Brazil: municipality of Alegre and municipality of Colatina. Twenty-one maize accessions were collected and evaluated for agronomic performance in two locations (The municipalities of Alegre and Colatina) in Espírito Santo State, Brazil. Trials were conducted under water-restricted conditions from vegetative to reproductive stage in a randomized block design with five replicates. Data were subjected to analysis of variance by the F Test and to multivariate clustering analysis according to the estimate of genetic distance proposed by Mahalanobis. Genotype by environment interaction identified promising genotypes for each specific environment. Maize germplasm accessions from the Ifes BAG showed genetic variability. Among the germplasm accessions from the Ifes BAG, the populations Padrinho, Piranão 14, Aliança and Palha Roxa are promising for breeding programs with the goal of increasing grain yield under water-restricted conditions in tropical climate regions.

Population structure and association mapping studies for yield-related traits in Maize (Zea mays L.)

Association mapping is an efficient approach for dissecting the genetic architecture of yield-related traits using single nucleotide polymorphism (SNP) markers in maize. The present study was carried out with a set of 93 diverse maize accessions with the objectives of analysing the population structure and conducting association mapping between SNP markers and yield-related traits viz. number of kernel rows per ear (NKR), number of kernel columns per ear (NKC), 100 grain weight (HGW) and grain yield (GY). Illumina golden gate assay containing 1536 SNPs distributed in all the chromosomes were used for genotyping 93 maize accessions. The population structure studies depicted the presence of five subpopulations, named ZM1, ZM2, ZM3, ZM4 and ZM5, contained 21, 16, 19, 12 and 25 accessions, respectively. Association mapping analysis carried out using mixed linear model (MLM), which is identified 36 marker-trait associations (MTAs) in the two years. Of these, 26 MTAs were detected either nearby or flanking the regions where the genomic regions have been reported. While, remaining10 MTAs were detected in the novel genomic region. The number of markers associated with each trait ranged from 6 (NKC) to 13 (HGW). We also found that one trait was associated with many markers (e.g., HGW with 13 markers), and single marker was also associated with multiple traits (eg. PZB00114_1 associated with HGW and GY). Our results provide good information for genetic architecture of yield-related traits and associated SNP markers could be valuable in implementing marker assisted selection (MAS) in maize breeding programs.

Association among Agro-morphological Traits by Correlations and Path in Selection of Maize Genotypes

In the State of Espírito Santo (Brazil), family farmers have grown a number of maize varieties for decades, consisting of open-pollinated populations with valuable importance for the livelihood of smallholder farmers. The study aimed to analyze the cause and effect of associations between agro-morphological traits for increasing yields in maize populations cultivated. A total of 16 maize accessions of in vivo conservation works in eight different locations were evaluated, in a randomized complete block design with three replicates, totaling 48 experimental units. Genetic parameters, genotypic, phenotypic, and environmental correlation were estimated, and a path analysis was conducted. In general, accessions presented enough genetic variability, showing significant differences for all traits analyzed statistically (P≤0.05). The first cob insertion height with plant height and final plant stand variables presented heritability (h2) higher than 80%, suggesting that superior genotypes could be determined. Highest estimates of phenotypic correlations (rp) were found between the first cob insertion height with plant height and total number of cobs with number of cobs per plant (0.85). For estimates of genotypic correlations (rg), the highest were between (i) the first cob insertion height and plant height; (ii) number of grains per row and number of cobs per plant; (iii) total number of cobs and final plant stand. Maize final plant stand and one thousand seed weight were observed to be traits that could be determinant in grain yield increase.

Variation in Agro-morphological Traits of Some Turkish Local Pop, Flint and Dent Maize (Zea mays L.)

Turkish maize accessions collected from north of Turkey were investigated for agro-morphologic variation in three maize kernel types (flint, pop and dent) including 79 accessions. Eight agronomic and morphologic traits (ear length, ear kernel row number, ear height, leaf number, 1000 kernel weight, tassel length, leaf width and leaf length) were analysed by ANOVA and principal component analysis. Varieties and accessions were found significantly different for variance components which were made up high variance due to accessions. Positive correlations were found between agronomic and morphologic traits. Multivariate discriminant function analysis with eight traits revealed that first two of multivariate correlation covered 86.6%, and next 69% of total variation among accessions and the first multivariate discriminant function had high eigenvalue with 76.8% of total variance between varieties belonged to flint and pop maize accessions while the second multivariate variable belonged to flint and dent maize accessions. These multivariate variables correctly classify three maize varieties maintaining maize accessions for their various characteristics with agronomic and morphological traits.

ПЕРСПЕКТИВЫ ИСПОЛЬЗОВАНИЯ ЗЕИНОВЫХ МАРКЕРОВ В СЕЛЕКЦИИ ЛИНИЙ И СОРТОВ ВОСКОВИДНОГО ПОДВИДА КУКУРУЗЫ

Background. Among the numerous maize accessions in the VIR collection, Plant special attention is drawn to the lines and varieties of waxy maize due to their specific feature, that is, the content of high-quality grain starch that consists entirely of amylopectin. This amylopectin starch is of special interest to the medical, starch and syrup, and confectionary industries. One of the most important applications of amylopectin starch in medicine is its use as a component of Volekam blood plasma substitute. Besides amylopectin, the grain of other maize subspecies contains much amylose starch which makes production of purified amylopectin expensive. Therefore, the creation and study of domestic waxy maize lines and varieties is very topical, however it is insufficiently developed at present. Materials and methods . For the first time, zein electrophoresis was used to analyze waxy maize old landraces and breeding lines. Zein electrophoresis was carried out in vertical 10% PAA gels with 8 M urea. The solution for zein extraction contained 6 M urea and 0.01 M dithiothreitol. Results. The present research pursued the following aims: to use zein elecrophoretic patterns (protein markers) in screening waxy maize landraces and lines for their identification and fingerprinting; to determine the biotype composition of landraces and their polymorphism and degree of relationship; and to demonstrate the possibility of applying zein markers in the development of new waxy maize inbred lines by backcrossing the wx1 gene into the initial dent maize line. Conclusions. Zein electrophoretic patterns showed the uniqueness of each waxy maize accession. All the studied new lines are united by a decreased intensity of most zein pattern components, as well as by the presence of an intensive component 47 which is absent in the pattern of the initial lines of dent maize. Component 47 may serve as a protein marker for identifying waxy maize lines. All landraces were found to be composed of several biotypes (from two to five). Regardless of the intravarietal polymorphism, every variety has specific patterns which facilitate its identification.

Discovery of Anthocyanin Acyltransferase1 (AAT1) in Maize Using Genotyping-by-Sequencing (GBS).

The reduced acylation phenotype describes the inability of certain accessions of maize (Zea mays [L.]) to produce significant amounts of acylated anthocyanins, which are typically the most abundant pigments. Acylated anthocyanins are important for their association with stability and are therefore important for the various industries using anthocyanins as natural colorants to replace synthetic dyes. Many anthocyanin acyltransferases have been characterized in other species; however, no anthocyanin acyltransferases have been characterized in maize. Therefore, a mapping population was developed from a cross between mutant stock 707G and wild-type acylation line B73 to identify the locus associated with the reduced acylation trait. High-performance liquid chromatography was used to assay the pigment content and composition of 129 F2 lines generated in the mapping population. Recessive alleles of Colorless1, Colored1, and the reduced acylation mutant all decreased anthocyanin content while Intensifier1 increased anthocyanin content in aleurone tissue. The association of increased proportions of acylation with increased anthocyanin content indicates acylation may be important for increasing the stability of anthocyanins in vivo. Genotyping-by-sequencing was used to create SNP markers to map the reduced acylation locus. In the QTL analysis, a segment of Chromosome 1 containing transferase family protein GRMZM2G387394 was found to be significant. A UniformMu Mu transposon knockout of GRMZM2G387394 demonstrated this gene has anthocyanidin malonyltransferase activity and will therefore be named Anthocyanin Acyltransferase1 (AAT1). AAT1 is the first anthocyanin acyltransferase characterized in a monocot species and will increase our knowledge of all acyltransferase family members.

Resistance Response of Maize Germplasm to Downy Mildew [Peronosclerospora philipinensis

&lt;p&gt;Two experiments to study responses of resistance of maize germplasm to downy mildew (Peronosclerospora philipinensis) have been conducted. Both experiments were arranged in randomized block design with two replication. The treatments in each experiment (2014 and 2016) were 70 maize accessions. The accessions were planted in planting distant of 75 cm × 20 cm, in 5 m rows, resulting in 20 plants per row. In every 10 rows, two check varieties were planted, i.e. one susceptible and one resistant variety. Ten days prior to planting, the soil was fertilized with mixed fertilizers consisted of urea, ZA, SP36, and KCl at a dose of 100, 100, 100, and 100 kg/ha, respectively. Fertilization II and III was given at 30 days after planting, and 45 days after planting with a dose of 100 kg urea/ha. As a source of inoculum downy mildew, around the repeated plot was planted with varieties Anoman variety (susceptible variety) that was inoculated with a suspension of downy mildew pathogen. Observation was conducted at 25, 35, and 55 days after planting, with the standard score of resistant to downy mildew, followed: 0–10% = resistant, 11–25% = moderately resistant, 26–50% = moderately susceptible, &amp;gt;50% = susceptible. The result of the experiments showed that there were 5 accessions resistant to downy mildew (P. philipinensis), i.e. CML 440×MR4-9-30-3, 664, 60, 572, and 554 with the intensity of downy mildew infection ranged from 5 to 10%. Twelve other accessions were classified as moderately resistant, i.e. CML 440×MR4-9-98-2, 440×MR4-9-98-4 CML, CML 440×MR4-9-124-1, 66, 71, 319, 108, 73, 48, 105, 554, and 682 with intensity of infection ranged from 13 to 25%. At the same experiments, the average intensity of downy mildew infection on susceptible check varieties reached 100 percent.&lt;/p&gt;

Diversidad genética en una población de maíz criollo (Zea mays L.) evaluada mediante marcadores microsatélites en Puerto Libertador, Córdoba

Maize a plant of Mesoamerican origin, has evolved in different microenvironments, generating the great diversity of maize that exists in the world. In order to determine the genetic diversity of a population of Creole maize, twelve microsatellite markers were evaluated in 30 accessions, in Puerto Libertador, Cordoba. The DNA of each accession was extracted using the PROMEGA kit, the markers were amplified by the PCR technique and the amplicons were run on polyacrylamide gels, the gels were digitalized and the molecular sizes were determined by an exponential model. Results showed a total of 66 alleles and an average of alleles of 5.5, the expected heterozygosity was 0.655, the values of the polymorphic information content (PIC) ranged from 0.352 to 0.838, with an average of 0.592 and the Hardy-Weinberg equilibrium showed imbalance (p <0.05). This work revealed that the studied accessions of Creole maize showed a high degree of polymorphism, high genetic variability and microsatellite markers were the appropriate for the evaluation of genetic diversity. This information shows to be useful for the conservation and protection of the genetic diversity of the studied Creole Maize.

Selection Signatures Underlying Dramatic Male Inflorescence Transformation During Modern Hybrid Maize Breeding.

Inflorescence capacity plays a crucial role in reproductive fitness in plants, and in production of hybrid crops. Maize is a monoecious species bearing separate male and female flowers (tassel and ear, respectively). The switch from open-pollinated populations of maize to hybrid-based breeding schemes in the early 20th century was accompanied by a dramatic reduction in tassel size, and the trend has continued with modern breeding over the recent decades. The goal of this study was to identify selection signatures in genes that may underlie this dramatic transformation. Using a population of 942 diverse inbred maize accessions and a nested association mapping population comprising three 200-line biparental populations, we measured 15 tassel morphological characteristics by manual and image-based methods. Genome-wide association studies identified 242 single nucleotide polymorphisms significantly associated with measured traits. We compared 41 unselected lines from the Iowa Stiff Stalk Synthetic (BSSS) population to 21 highly selected lines developed by modern commercial breeding programs, and found that tassel size and weight were reduced significantly. We assayed genetic differences between the two groups using three selection statistics: cross population extended haplotype homozogysity, cross-population composite likelihood ratio, and fixation index. All three statistics show evidence of selection at genomic regions associated with tassel morphology relative to genome-wide null distributions. These results support the tremendous effect, both phenotypic and genotypic, that selection has had on maize male inflorescence morphology.

Mutator-Based Transposon Display: A Genetic Tool for Evolutionary and Crop-Improvement Studies in Maize.

Transposable elements account for up to 85% of the maize genome and have significant implications in crop-improvement and evolutionary analyses. The Mutator (Mu) transposon superfamily, a class of DNA transposons, comprises the most complex and active elements in the maize genome, suggesting a special role in plant evolution. Here, we designed a set of Mu-specific primers based on terminal invert repeats and used a transposon display (TD) method for genotyping. We analyzed the distribution pattern of Mu insertions in teosinte (wild relative), sorghum (distant relative), and domesticated maize accessions (dent, sweet, and waxy). The MU-TD analysis suggested the presence of high polymorphic insertions among the species and subspecies, indicating the utility of the method in studying genetic variation and species relationships. Furthermore, we analyzed 80 maize recombinant inbred line populations. Mu-TD generated an average of 60% Mu-anchored polymorphic fragments in which insertions appeared to be segregating in significantly high numbers. The amplification profile was highly reproducible, confirming the utility of Mu elements as a new set of TD markers for developing high-density genetic maps.