Is Flint Corn Naturally Resistant to Maize Weevil Infestation?

Sitophilus zeamais (maize weevil) is one of the most destructive pests of maize stored in tropical and subtropical regions. This study determined the resistance of flint corn and dent corn to infestation by S. zeamais (Motschulsky), the maize weevil. Improved King Philip hybrid flint corn and Fontanelle 6T-510 hybrid dent corn were used in this experiment. Two temperature conditions (10 °C and 27 °C) and two storage times (15 days and 30 days) were used. Results showed that flint corn was more resistant to insect damage than dent corn at 27 °C and 30 day storage time. After 30 days storage time and 27 ºC death rate was significantly higher in flint corn (R2 = 0.945) compared to (R2 = 0.634) in dent corn. Damaged seed was 10% higher in dent corn then in flint corn at 27 ºC and 30 days. However, no significant difference was observed for seed weight loss between flint corn and dent corn at the same storage conditions. Both dent and flint corn are extensively cultivated in developing countries. It appears that storage of flint corn may be one promising solution to reducing corn damage and infestation problems in the tropics and in developing countries, but more research is needed

The Origin of Cornbelt Maize: The Isozyme Evidence

Historical records show t hat the Midwestern dent corns of the United States originated from hybridization of two landraces, Northern Flint and Southern Dent. We examined the origin of Southern and Midwestern Dents by means of isozyme electrophoresis. Isozyme genotypes were determined for 23 loci in 12 plants each of 32 accessions of Southern Dent. Previously published isozyme data for maize landraces of Mexico and North America and for U.S. Midwestern Dents were included for comparative purposes. The data show that Northern Flint and Southern Dent are among the isozymically most divergent maize landraces. Nei’s genetic identities between populations of these two landraces are very low for conspecific populations (ca. 0.80). Southern Dent of the southeastern U.S. appears closely related to similar dent corns of southern Mexico, supporting a previously published hypothesis that U.S. Southern Dent is largely derived from the dent corns of southern Mexico. The Midwestern Dents, which resulted from crosses of Southern Dent and Northern Flint, are much more like Southern Dent than Northern Flint in their isozyme profile. Similarly, public inbreds show greater affinity to Southern Dent with the exception of sweet corn lines, which resemble Northern Flint in their isozyme allele frequencies. North American public inbreds do not contain appreciable isozymic variation beyond that found in Northern Flint and Southern Dent

The pattern and distribution of deleterious mutations in maize

Most non-synonymous mutations are thought to be deleterious because of their effect on protein sequence. These polymorphisms are expected to be removed or kept at low frequency by the action of natural selection, and rare deleterious variants have been implicated as a possible explanation for the "missing heritability" seen in many studies of complex traits. Nonetheless, the effect of positive selection on linked sites or drift in small or inbred populations may also impact the evolution of deleterious alleles. Here, we made use of genome-wide genotyping data to characterize deleterious variants in a large panel of maize inbred lines. We show that, in spite of small effective population sizes and inbreeding, most putatively deleterious SNPs are indeed at low frequencies within individual genetic groups. We find that genes showing associations with a number of complex traits are enriched for deleterious variants. Together these data are consistent with the dominance model of heterosis, in which complementation of numerous low frequency, weak deleterious variants contribute to hybrid vigor

Transcriptome-Wide Association Supplements Genome-Wide Association in Zea mays.

Modern improvement of complex traits in agricultural species relies on successful associations of heritable molecular variation with observable phenotypes. Historically, this pursuit has primarily been based on easily measurable genetic markers. The recent advent of new technologies allows assaying and quantifying biological intermediates (hereafter endophenotypes) which are now readily measurable at a large scale across diverse individuals. The usefulness of endophenotypes for delineating the regulatory landscape of the genome and genetic dissection of complex trait variation remains underexplored in plants. The work presented here illustrated the utility of a large-scale (299-genotype and seven-tissue) gene expression resource to dissect traits across multiple levels of biological organization. Using single-tissue- and multi-tissue-based transcriptome-wide association studies (TWAS), we revealed that about half of the functional variation acts through altered transcript abundance for maize kernel traits, including 30 grain carotenoid abundance traits, 20 grain tocochromanol abundance traits, and 22 field-measured agronomic traits. Comparing the efficacy of TWAS with genome-wide association studies (GWAS) and an ensemble approach that combines both GWAS and TWAS, we demonstrated that results of TWAS in combination with GWAS increase the power to detect known genes and aid in prioritizing likely causal genes. Using a variance partitioning approach in the largely independent maize Nested Association Mapping (NAM) population, we also showed that the most strongly associated genes identified by combining GWAS and TWAS explain more heritable variance for a majority of traits than the heritability captured by the random genes and the genes identified by GWAS or TWAS alone. This not only improves the ability to link genes to phenotypes, but also highlights the phenotypic consequences of regulatory variation in plants

GETTING TECHNOLOGY AND THE TECHNOLOGY ENVIRONMENT RIGHT: LESSONS FROM MAIZE DEVELOPMENT IN SOUTHERN AFRICA

This paper examines two questions: (1) what were the most important factors that led to differential rates of adoption of maize technology by farmers in Zimbabwe, Zambia, and Malawi from 1910 to 1995? and (2) what do these experiences suggest about strategic investments in institutions and organizations needed to create a sustainable environment for technology development and adoption in the future? The analysis suggests that productivity increases are facilitated by (a) technology innovations throughout the agricultural system, (b) integration of technological innovations with changes in policies, organizations, human capital and infrastructure related to extension, input and output markets and processing services, and (c) coordination of these innovations across different stages of the agricultural system.Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

Importance of appropriate selection environments for breeding maize adapted to organic farming systems

Organic farming systems, characterized by special attention to soil fertility, recycling techniques and low external inputs, gained increased significance in recent years. As a consequence, there is a growing demand for varieties adapted to organic and/or low input farming. The objectives of the present study were to (i) compare the testcross performance of segregating maize (Zea mays) populations under established organic (OF) and conventional farming (CF) systems, (ii) determine quantitative genetic parameters decisive for the selection response under OF vs CF conditions, and (iii) draw conclusions for breeding new varieties optimally adapted to OF. Testcross performance of four different material groups of preselected lines (90 lines per group) derived from early European breeding material was assessed under OF and CF in three different geographic regions in Germany in 2008. Grain yields under OF were 3 to 18% lower than under CF in the individual experiments depending on the test region and, to a lesser extent, on the genetic material. On average, grain dry matter yield under OF was 1077 g m-2 compared to 1186 g m-2 under CF. Phenotypic correlations between OF and CF were small or moderate for grain yield in each of the four material groups (0.22 to 0.45), while strong and highly significant correlations were found for dry matter content (0.89 to 0.94). Genotypes with top grain yields under OF often did not show this superiority under CF and vice versa. Despite considerable heterogeneity of the OF test sites, the heritability for grain yield was in the same order of magnitude under OF and CF. It is concluded that test sites managed by OF are indispensable for making maximum progress in developing maize varieties for these conditions

Maize open-pollinated populations physiological improvement: validating tools for drought response participatory selection

Participatory selection—exploiting specific adaptation traits to target environments—helps to guarantees yield stability in a changing climate, in particular under low-input or organic production. The purpose of the present study was to identify reliable, low-cost, fast and easy-to-use tools to complement traditional selection for an e ective participatory improvement of maize populations for drought resistance/tolerance. The morphological and eco-physiological responses to progressive water deprivation of four maize open-pollinated populations were assessed in both controlled and field conditions. Thermography and Chl a fluorescence, validated by gas exchange indicated that the best performing populations under water-deficit conditions were ‘Fandango’ and to a less extent ‘Pigarro’ (both from participatory breeding). These populations showed high yield potential under optimal and reduced watering. Under moderate water stress, ‘Bilhó’, originating from an altitude of 800 m, is one of the most resilient populations. The experiments under chamber conditions confirmed the existence of genetic variability within ‘Pigarro’ and ‘Fandango’ for drought response relevant for future populations breeding. Based on the easiness to score and population discriminatory power, the performance index (PIABS) emerges as an integrative phenotyping tool to use as a refinement of the common participatory maize selection especially under moderate water deprivationinfo:eu-repo/semantics/publishedVersio

Genes involved in barley yellow dwarf virus resistance of maize

KEY MESSAGE: The results of our study suggest that genes involved in general resistance mechanisms of plants contribute to variation of BYDV resistance in maize. ABSTRACT: With increasing winter temperatures in Europe, Barley yellow dwarf virus (BYDV) is expected to become a prominent problem in maize cultivation. Breeding for resistance is the best strategy to control the disease and break the transmission cycle of the virus. The objectives of our study were (1) to determine genetic variation with respect to BYDV resistance in a broad germplasm set and (2) to identify single nucleotide polymorphism (SNP) markers linked to genes that are involved in BYDV resistance. An association mapping population with 267 genotypes representing the world’s maize gene pool was grown in the greenhouse. Plants were inoculated with BYDV-PAV using viruliferous Rhopalosiphum padi. In the association mapping population, we observed considerable genotypic variance for the trait virus extinction as measured by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and the infection rate. In a genome-wide association study, we observed three SNPs significantly [false discovery rate (FDR) = 0.05] associated with the virus extinction on chromosome 10 explaining together 25 % of the phenotypic variance and five SNPs for the infection rate on chromosomes 4 and 10 explaining together 33 % of the phenotypic variance. The SNPs significantly associated with BYDV resistance can be used in marker assisted selection and will accelerate the breeding process for the development of BYDV resistant maize genotypes. Furthermore, these SNPs were located within genes which were in other organisms described to play a role in general resistance mechanisms. This suggests that these genes contribute to variation of BYDV resistance in maize. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00122-014-2400-1) contains supplementary material, which is available to authorized users

Variation in the grain properties of maize hybrids with different grain hardness characteristics and their response to nitrogen fertilizer in terms of milling quality : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science (Seed Technology) at Massey University

The proportion of grits and flour produced during the dry milling of maize (Zea mays L.) grain is related to the ratio of hard to soft endosperm. The quality standards required vary widely with different end uses, and for dry milling a hybrid with a 'hard' endosperm will usually yield the highest proportion of grits. The texture of the maize endosperm is variable and depends on the maize hybrid and agronomic conditions. In general the available literature showed protein concentration of the grain can be improved by nitrogen fertilizer application, and as the protein content increases, the amount of hard endosperm increases along with value to the miller. A field trial to investigate the effect of nitrogen fertilizer on grain yield and quality, especially grain protein content and hardness, was carried out at the Frewens block, Massey University in the 1994/95 season. Three maize hybrids (P3751, P3787 and A82-8 xNZ84) with three different endosperm textures (soft, intermediate and hard) were grown at two sowings (October and November) with three different nitrogen levels (0, 250, 500kg urea/ha). Urea fertilizer was applied as a side dressing and split into three application times, i.e. at the three leaf stage, at canopy closure and at the 50% silking stage. Plant growth and development were measured by counting the leaf number and leaf appearance rate, formation of the black layer and grain moisture dry down for each hybrid. Grain yields and yield components were measured for different nitrogen treatments at both sowings. Grain protein content was measured from total nitrogen percentage as determined by the Macro Kjeldhal method. Grain hardness was measured by a Stenvert Hardness Tester, while bulk density and grain moisture content were measured by a grain analysis computer. The total number of leaves per plant was greater in hybrid A82-8xNZ84 than hybrids P3787 and P3751 at both sowings, but rate of leaf appearance was faster for the November sowing than the October sowing. Formation of the 'black layer' (i.e physiological maturity) and moisture dry down rate was faster in hybrid P3787 than in hybrids P3751 and A82-8xNZ84 at both sowings. Grain yield was significantly increased at both sowings by the application of 250kg/ha urea, but not by the 500kg urea/ha treatment. Hybrid A82-8xNZ84 gave the highest yield and P3787 gave the lowest. The main yield components which differed between hybrids were number of grains per cob and 100-grain weight. Grain protein content increased progressively in response to the applied nitrogen fertilizer. Protein percentage increased from 8.81% in the control to 10.13% for 500kg urea/ha in the October sowing, and 8.72% in the control to 10.13% for 500kg urea/ha in the November sowing. At both sowings all three hybrids contained the highest amount of protein at the highest urea treatment i.e. 500kg urea/ha. Increased nitrogen application improved grain hardness. For those grains grown under higher nitrogen levels grinding resistance time, energy required for grinding and milling duration time were higher than grains grown when no urea was applied. Grain bulk density (test weight) increased as nitrogen increased. Hybrids A82-8xNZ84 and P3787 had higher grain hardness under the high nitrogen treatment than hybrid P3751. There was a strong, positive relationship between grain protein content and Stenvert Hardness Test parameters at both sowings. When nitrogen was applied grain contained a higher amount of protein (which presumably made grain harder) than the no applied nitrogen treatment. Inherent endosperm texture was not changed by the increased protein percentage as the soft endosperm hybrid did not show an improved hardness, but the intermediate and hard endosperm hybrids showed an improvement in this regard. Results from both sowings indicated grain yield, protein and hardness quality can be improved by applying nitrogen fertilizer. This has implications for dry milling, where hard grain is a necessity for higher grits recovery