Sweet Corn Populations Research Articles

Prediction of resistance, virulence, and host-by-pathogen interactions using dual-genome prediction models

Key messageIntegrating disease screening data and genomic data for host and pathogen populations into prediction models provides breeders and pathologists with a unified framework to develop disease resistance.Developing disease resistance in crops typically consists of exposing breeding populations to a virulent strain of the pathogen that is causing disease. While including a diverse set of pathogens in the experiments would be desirable for developing broad and durable disease resistance, it is logistically complex and uncommon, and limits our capacity to implement dual (host-by-pathogen)-genome prediction models. Data from an alternative disease screening system that challenges a diverse sweet corn population with a diverse set of pathogen isolates are provided to demonstrate the changes in genetic parameter estimates that result from using genomic data to provide connectivity across sparsely tested experimental treatments. An inflation in genetic variance estimates was observed when among isolate relatedness estimates were included in prediction models, which was moderated when host-by-pathogen interaction effects were incorporated into models. The complete model that included genomic similarity matrices for host, pathogen, and interaction effects indicated that the proportion of phenotypic variation in lesion size that is attributable to host, pathogen, and interaction effects was similar. Estimates of the stability of lesion size predictions for host varieties inoculated with different isolates and the stability of isolates used to inoculate different hosts were also similar. In this pathosystem, genetic parameter estimates indicate that host, pathogen, and host-by-pathogen interaction predictions may be used to identify crop varieties that are resistant to specific virulence mechanisms and to guide the deployment of these sources of resistance into pathogen populations where they will be more effective.

Effect of full‐sib and S2‐selection on a sweet corn population (Zea mays convar. saccharata)

AbstractSweet corn breeding goals differ from grain or silage corn. Sweet corn goals focus on marketable yield including several quality traits. This study explores the effect of a single cycle of full‐sib selection and S2 selection on improving the marketable yield of an open‐pollinated sweet corn population. The selected populations were subsequently compared in four environments for several plant‐, yield‐ and quality traits relative to the original population. Analysis of variance was used to detect selection progress and indirect effects of selection. Full‐sib and S2‐selection decreased total yield. Marketable yield was decreased more by S2‐selection than by full‐sib selection. Flowering time was changed by full‐sib selection, but not by S2‐selection. Full‐sib selection improved ear quality by increasing ear length, the diameter of the ear and the number of kernel rows. S2‐selection showed no effect or a negative effect on ear quality. The application of a single cycle of selection using either method seemed inadequate for increasing marketable yield. More cycles might be necessary to make significant improvements.

Assessment of frequency distribution for the morphological and yield related traits in BC1F1, BC2F1 and BC2F2 populations in sweet corn

The nature of gene action and the number of genes controlling the traits are the vital criteria for the selection of traits. The present study is to analyze the range of variations within the population and as well as the skewness and kurtosis in backcross and selfed sweet corn populations USC1-2-3-1× UMI1230β+ and SC1107×UMI1230β+. In the BC2F2 population of SC1107×UMI1230β+, most of the traits showed positive skewness and platykurtic distribution which indicated that complementary gene action  played a role and more number of genes is controlling the traits. In USC1-2-3-1× UMI1230β+, single plant yield recorded positive skewness. In some traits such as, the number of tassel branches, cob girth, and leaf breadth showed negative skewness and platykurtic distribution was also observed in both the cross combination which indicated prevalence of duplicate gene action. In order to fix an individual trait and for rapid genetic gain, duplicate gene action is required.  Keywords: Sweet corn, Skewness, Kurtosis, Gene action.&nbsp

Recurrent haploid selection in a population of sweet corn (Zea mays convar. saccharata)

AbstractRecurrent haploid selection is based on the phenotype of haploid plants. This selection method was reported to be very effective because of the high selection pressure. The aim of this study was to quantify the effect of five generations of recurrent haploid selection on a sweet corn population developed by intercrossing 40 hybrid cultivars. We compared the initial population, five cycles of recurrent haploid selection, and mass selection after five cycles in six environments. The results indicated that recurrent haploid selection had no positive effect on yield or quality. For the traits tillering, tip fill, total yield and total number of ears, significant changes from cycle to cycle were observed but in differing directions. The performance per se of single haploid plants has probably a low correlation to their combining ability in a population. Positive mass selection of the best ears resulted in no improvement of total yield, a reduction of marketable yield and about 2‐day delay of flowering. In conclusion, recurrent haploid selection based on the phenotype of individual plants was not an efficient method to improve the sweet corn population investigated.

Limited‐transpiration rate and plant conductance in a diverse sweet corn population

AbstractLimited‐transpiration rate at elevated vapor pressure deficit (VPD) can allow soil water conservation for use during late‐season drought, but it can also result in decreased crop yields under well‐watered conditions because of restricted crop gas exchange. Previous studies with sweet corn (Zea mays L.) have found the limited‐transpiration rate was quite common among commercial cultivars even though sweet corn is commonly grown under well‐watered conditions. This study was undertaken to identify possible genetic sources of sweet corn that were not encumbered by the limited‐transpiration trait. Additionally, data were obtained to compare the plant hydraulic conductance among the lines. Among the 26 sweet corn lines included in this study, only eight did not express the limited‐transpiration trait. Four of the lines not expressing the limited‐transpiration (IL395a, IL543c, P39, and SD245) had stomata vapor conductance values over the range of tested VPD similar to the values expressed by many of the limited‐transpiration lines only at low VPD. The eight lines not expressing the limited‐transpiration trait tended to have low plant hydraulic conductance. For those lines expressing the limited‐transpiration trait, there was a correlation between the VPD at initiation of limited transpiration and plant hydraulic conductance. Expression of the limited‐transpiration traits proved, however, to be temperature sensitive in 7 of 18 tested lines expressing the trait at 32 °C because they failed to express the trait at 38 °C. The genetic variation in expression of the limited‐transpiration trait and plant hydraulic conductance identified in this study offers specific candidate inbred lines that could be used as genetic resources for improving sweet corn growth and yield for well‐watered environments.

Classical and genomic prediction of synthetic open‐pollinated sweet corn performance in organic environments

AbstractOpen‐pollinated cultivars provide a number of benefits for organic and smallholder farmers, allowing them to save seed, conduct on‐farm selection, and maintain on‐farm crop genetic diversity. Synthetic open‐pollinated cultivars provide advantages over traditional open‐pollinated cultivars for such farmers. The objective of this research was to determine the usefulness of marker‐based prediction models relative to structured mating design‐based predictions for selecting untested sweet corn synthetic cultivars for organic production systems. This study used marker data and phenotypic data collected in 2015 and 2016 in 11 organic trials across six locations on 40 sweet corn (Zea mays L.) inbreds and 100 hybrid progeny formed from four disconnected North Carolina Design II (NC DII) mating blocks to predict performance of untested synthetic open‐pollinated sweet corn populations. In 2017, validation trials of 26 previously untested synthetic populations were grown in five organic environments to assess correlations between actual performance and performance predicted by genomic best linear unbiased prediction (GBLUP) or NC DII general combining abilities (GCAs). Correlations between values measured in 2017 validation trials and values predicted from the complete dataset ranged from 0.28 to 0.68 for GCA‐based predictions, from 0.25 to 0.67 for the additive GBLUP model, and from 0.28 to 0.68 for the additive plus dominance GBLUP model. In general, neither the genomic prediction model with solely additive effects nor genomic prediction with both additive and dominance effects demonstrated consistent increases in accuracy of predictions of synthetic population performance above predictions based solely on general combining ability. However, genomic prediction could be used to predict synthetic populations that shared alleles with the training set, even if the parents were never included in the training set, which is not possible with traditional general combining ability models.

Selection indices for agronomic and chemical traits in segregating populations of sweet corn

In the sweet corn breeding, the selection of superior genotypes should consider many traits simultaneously. The best strategy to select traits simultaneously is through selection indices. This study aimed to verify traits that have direct effect about grain yield (GY) in order to compose the selection indices and to compare these indices on sweet corn populations. Eighteen traits were evaluated in eight genotypes of sweet corn belonging to generation F3. The data were submitted to analyses of variance and path coefficient analyses. We compared the direct and indirect selection and the following indexes: base, classical, desired gain and genotype-ideotype distance. According to path coefficient analyses, the traits which showed a direct effect about GY were stand, number of ears, ear diameter, number of grains per row and industrial yield, which composed the indices. The base index provided the greatest total genetic gain, desired gains on all traits, uniform distribution of the gains and considerable gains on GY.

Selection indexes for agronomic and chemical traits in segregating sweet corn populations

ABSTRACT In the sweet corn breeding, the selection of superior genotypes should consider many traits simultaneously. The best strategy to select traits simultaneously is through selection indexes. This study aimed to compare the efficiency of different selection indexes based on characteristics with direct effect on grain yield in segregating sweet corn populations. Eighteen traits were evaluated in eight sweet corn genotypes on generation F3. Data were submitted to analyses of variance and path coefficient analyses. We compared the direct and indirect selection and the following indexes: base, classical, desired gains and genotype-ideotype distance. According to path coefficient analyses, the traits which showed a direct effect about grain yield (GY) were stand, number of ears, ear diameter, number of grains per row and industrial yield, which composed the indexes. The base index provided the greatest total genetic gain, desired gains on all traits, uniform distribution of the gains and considerable gains on GY.

Recurrent Full-sib Family Selection for Husk Extension in Sweet Corn

Corn earworm (Helicoverpa zea) is a costly and destructive pest in sweet corn (Zea mays) production. A recurrent selection experiment was conducted to assess the feasibility of selecting a sweet corn population for longer husks without shortening the ears and to determine whether direct selection for longer husks confers improved resistance to the corn earworm. The initial population was derived from crosses between long- and tight-husked inbred lines (A684su, A685su, and A686su) originally selected for resistance to the european corn borer (Ostrinia nubilalis) and a high-quality commercial hybrid parent (‘Super Sweet Jubilee Plus’). Three cycles of recurrent full-sib family selection were conducted from 2014 to 2016, with a selection intensity of ≈10% per cycle. In 2017, the cycles of selection were evaluated and compared with common commercial cultivars for husk extension, ear length, rate of corn earworm infestation, and extent of corn earworm damage. Ears were artificially infested with corn earworm eggs suspended in an agar solution. The population was successfully selected for longer husk extension without shortening the ears, but the increase in husk extension did not correspond to an increase in corn earworm resistance. Further evaluation is needed to determine whether long husk extension is ineffective as a source of corn earworm resistance, whether it is more effective in combination with other resistance traits, whether greater differences in husk extension are needed to confer biologically significant differences in corn earworm resistance, or whether improved inoculation methods could improve differentiation between genotypes.

Genetic damage in Mexican and South American sweet corn varieties due to the use of herbicides (Nicosulfuron and Topramezone)

In order to encourage corn production, several herbicides such as nicosulfuron and topramezone are used. Though they offer great advantages, they may affect crop productivity and may even induce DNA damage. This study evaluated genotoxic activity at two nicosulfuron concentrations (40,000 and 80, 000 ppm) and at four topramezone concentrations (1480, 148, 14.8 and 1.48 ppm) in sweet corn and hybrid populations from Mexico and South America. NCMAMD were used in 113 variety accessions from Mexico and South America and on 5 commercial hybrids for nicosulfuron and 9 accessions and a hybrid for topramezone. Both nicosulfuron concentrations induced significant genetic damage (P < 0.01) on sweet corn and on normal hybrids. Topramezone showed significant genotoxic activity (P < 0.01) on both sweet corns and normal hybrids. On both sweet corns and normal hybrids, the original situation did not provide protection from genetic damage caused by herbicides and all showed significant genetic damage (P < 0.01) compared to their corresponding negative controls. This paper clearly shows nicosulfuron and topramezone genotoxicity and the study with comet assay in SCAMCN indicated that corn can be used as an excellent biomonitor for genotoxicity assessment.

SUPER SWEET CORN BREEDING BY BACKCROSS: A NEW CHOICE FOR THE BRAZILIAN MARKET

The sweet corn market has been expanding in recent years and the trend is to maintain this growth, targeting mainly the export market. The goal was to evaluate the agronomic performance per se and hybrid backcrosses of four sweet corn populations and to estimate genetic parameters inherent in these populations, in order to achieve promising lines to obtain hybrids. The following genotypes were used for a test: the donor population sh gene, two recurring populations interpopulation hybrids of common maize, four sweet corn populations, and four sweet corn interpopulation hybrids. The traits evaluated were: plant height, stand, number of ears, prolificacy, number of grain rows, as well as average ear diameter, average diameter cobs, average husked ear length, average unhusked ear length, average unhusked ear weight, average husked ear weight, ear relationship, unhusked ear yield and husked ear yield. The backcross method was efficient for obtaining sweet corn populations with good agronomic performance. Because the sweet corn interpopulation hybrid presents agronomic performance similar toP8 x C8 interpopulation hybrid, it can be inferred that all sweet corn populations backcrossed are recommended for use in obtaining lines, in order to obtain productive hybrids, or even directly as hybrid trade after further assessments.

Recurrent Selection and Participatory Plant Breeding for Improvement of Two Organic Open-Pollinated Sweet Corn (Zea mays L.) Populations

Organic growers face unique challenges when raising sweet corn, and benefit from varieties that maintain high eating quality, germinate consistently, deter insect pests, and resist diseases. Genotype by environment rank changes can occur in the performance of cultivars grown on conventional and organic farms, yet few varieties have been bred specifically for organic systems. The objective of this experiment was to evaluate the changes made to open-pollinated sweet corn populations using recurrent selection and a participatory plant breeding (PPB) methodology. From 2008 to 2011, four cycles of two open-pollinated (OP) sweet corn populations were selected on a certified organic farm in Minnesota using a modified ear-to-row recurrent selection scheme. Selections were made in collaboration with an organic farmer, with selection criteria based on traits identified by the farmer. In 2012 and 2013, the population cycles were evaluated in a randomized complete block design in two certified organic locations in Wisconsin, with multiple replications in each environment. Significant linear trends were found among cycles of selection for quantitative and qualitative traits, suggesting the changes were due to recurrent selection and PPB methodology for these populations. However, further improvement is necessary to satisfy the requirements for a useful cultivar for organic growers.

Factors Affecting Doubled Haploid Plant Production Via Maize Technique in Bread Wheat

Abstract The effect of two in planta factors (growth conditions, genotype) and two in vitro factors (time of embryo rescue, embryo rescue medium) on doubled haploid (DH) plant production in bread wheat via maize technique was investigated in nine F1 hybrids produced after crossing four bread wheat cultivars. During the first year one group of F1 plants was grown in a field and at the proper stage pollinated with maize pollen (sweet corn popu-lation). In parallel, a second group of F1 plants was grown in a growth chamber and pollinated as in the former group. In the second growing season the experiment was repeated but only field-grown plants were used. All the produced haploid embryos were cultured in three different media and the resulting 146 haploid plants were sub-sequently treated with aqueous solution of colchicine. Finally, 86 doubled haploid plants were obtained. We noted that the growing conditions of the parental plants and the intervening time between day of pollination and day of embryo rescue influenced the percentage of haploid embryo production. Culture medium also influenced haploid and doubled haploid plant production. The two media (MS/2, B5) were found equally effective. Most of the haploid embryos originated from the Penios × Acheloos cross, whereas most of the doubled haploid plants were produced from the KVZ × Penios cross. Doubled haploid plants were produced from all crosses.

Recurrent Selection for Seedling Growth of Sweet Corn in Cool Temperatures

ABSTRACTEarly spring sweet corn producers would benefit from supersweet cultivars with improved seedling cold tolerance. We performed recurrent selection for improved seedling vigor and germination rates at cool temperatures in three sweet corn populations. The original populations were formed by crossing temperate sweet corn and High‐altitude Mexican germplasm. A sugary1 (su1) and a shrunken2 (sh2) population derived from Cacahuacintle Dulce germplasm were evaluated, as well as a sh2 population derived from ‘Maíz Dulce’. The most uniformly vigorous seedling lots were chosen by replicated visual selection and then intermated to form the next cycle. The direct effects of selection were measured through growth chamber germination tests at 10°C. The indirect effects of selection were assessed through replicated field trials. A positive significant linear response to selection for seedling length was present in the two sh2 populations (R2 = 0.92, P &lt; 0.001; R2 = 0.94, P &lt; 0.001). There was a 71% increase in seedling length over four cycles of selection in one sh2 population, and a 116% increase in the other. Significant linear decreases in the average number of dead kernels were observed in both sh2 populations (R2 = 0.91, P &lt; 0.05; R2 = 0.89, P &lt; 0.05). There were no significant changes in kernel carbohydrate composition in either of the sh2 populations. No linear changes were observed as a direct response to selection in the su1 population. While germination under field conditions improved for both of the sh2 populations, selection had a negative effect on several agronomic traits, including plant height, ear height, and ear weight, suggesting the possibility of inbreeding during recurrent selection.

Identification of a major quantitative trait locus for ear size induced by space flight in sweet corn.

The development of molecular markers has contributed to progress in identifying the gene(s) responsible for favorable variations in maize studies. In this study, quantitative trait locus (QTL) mapping was conducted using simple sequence repeat markers in an F2 sweet corn population from a cross between parental line 1132 and space flight-induced mutant line 751 to identify the loci contributing to an increase in some yield traits. A primary mutated genomic region was located on chromosome 9. In total, 26 QTL were detected for eight yield-related traits and assembled into three clusters on chromosome 9. The largest QTL cluster at bin 9.02/03, primarily contributing to >10% of the phenotypic variation in ear and cob diameters, was likely due to a major QTL. Desired alleles of these QTL were provided by the mutant line 751. The primary action of the major mutant allele was an additive effect. Another mutant locus, which was induced in bin 9.01, increased cob and ear diameters by dominant genetic action.

Agronomic performance of sweetcorn populations derived from crosses between sweetcorn and field corn

The adaptation of sweetcorn (Zea mays L.) to Spanish growing conditions needs to be improved, something that could be achieved by incorporating traits from field corn populations. The aim of the present study was to analyse the performance of sweetcorn populations carrying the genes sugary1 (su1) or shrunken2 (sh2), as well as sugary enhancer double mutants (su1 se1), produced by crosses between sweetcorn donor populations and the Spanish field corn populations Lazcano, Oroso and Rastrojero. The three field corn populations plus the su1, su1 se1 and sh2 populations derived from them, as well as the su1, su1 se1, and sh2 donor populations used in the crosses with the field corn populations, were evaluated for their agronomic performance. Several hybrids were used as controls. Assessments were made in Zaragoza (NE Spain) and Pontevedra (NW Spain) over two years. The ability of the field corn populations to improve the sweetcorn varieties was not greatly affected by the sweetcorn mutant involved. The field corn populations chosen as donors for improving sweetcorn must depend on the growing conditions in mind. Sweetcorn populations derived Oroso would appear to be the most favourable for northern Spain, while those derived from Rastrojero would appear to be the most suitable for inland Spain, although other field corn populations are still to be examined.

Divergent Selection for Vegetative Phase Change in Maize and Indirect Effects on Response to Puccinia sorghi

In maize (Zea mays L.), some experiments have indicated that early vegetative phase transition is associated with increased resistance to disease, insects, and stalk lodging. The sweet corn population Minn11 was selected over three cycles of divergent recurrent selection for early‐phase transition and late‐phase transition. Objectives were to determine the effectiveness of divergent recurrent selection and if the divergent selection program was associated with resistance to common rust (Puccinia sorghi). Selection resulted in a significant linear response for last leaf with juvenile wax in both the early and late directions of selection. The third cycle in the late direction (C3L) had two more leaves with juvenile wax than cycle zero (C0). The third cycle in the early direction (C3E) had 1.5 fewer leaves with juvenile wax than C0. To determine the effects of divergent selection for vegetative phase change on response to common rust the populations were inoculated with rust at three developmental times, vegetative stage (v) 5, v10, and v15, and rust damage was rated on leaves 7 through 13 individually, resulting in 21 potential responses for each direction of selection. Among the 21 leaf by developmental stage combinations, there were 9 significant linear trends in the late direction of selection. Most of the linear trends were detected in leaves 7 through 9. Selection for early transition did not affect response to common rust. The amount of leaf area damaged by rust in C3E never differed from the amount in C0.

Genetic Variability and Responses to Two Methods of Recurrent Selection in Two Sweet Corn (Zea mays L. Saccharata) Populations

Genetic Variability and Responses to Two Methods of Recurrent Selection in Two Sweet Corn (Zea mays L. Saccharata) Populations

Genetic variation among and within sweet corn populations detected by RAPD and SSR markers

Genetic variation among and within sweet corn populations detected by RAPD and SSR markers

Responses to Recurrent Selection Methods in Two Sweet Corn (Zea mays L. saccharata) Populations

Responses to Recurrent Selection Methods in Two Sweet Corn (Zea mays L. saccharata) Populations