Maize Breeding Research Articles

Heritability and Selection Using GGE Biplots and the Sustainability Index (SI) of Maize Mutants under Different Cropping Systems in Upland

A good maize plant breeding program must consider the effect of genotype-by-environment interactions (GEIs) and the correlation of important traits. The purpose of this study was to evaluate genetic variation, identify and investigate the implications of GEIs on breeding maize mutants in order to determine the ideal genotypes (stable and high yield), identify the best intercropping system for maize mutants, and identify the heritability and relationships of the traits tested that are important in cultivation. This research was carried out in five different intercropping systems in Upland West Java, Indonesia. A randomized block design with two replications was used in the field experiment. The measurement results revealed that the genetic diversity of maize mutants is broad, with six axes having eigenvalues ranging from 8.76 to 1.07 and a cumulative value of 76.64%. The neighbor-joining tree also showed a wide range of variation, yielding five distinct groups. The GEIs had a significant effect on the 14 traits tested, particularly yield. The environment had a significant impact on the variation of all the traits tested. The ideal cropping system for selecting the ideal maize mutant was Environment 4 (maize + rice). Superior maize mutants were successfully selected based on the GGE biplot. Thus, the sustainability index (SI) was used to successfully select maize mutants that were superior by 20.00%. These two methods selected only 15.00% of the maize mutants. One trait has a low heritability value, five traits have a moderate heritability value, and 17 traits have a high heritability value. The yields correlated positively and significantly with nine yield traits. Future maize-breeding programs can be based on data on genetic diversity, heritability, and the relationship of the traits tested. The best intercropping system can be used as an alternative for increasing maize cultivation income. Selected maize mutants can be proposed as new superior genotype candidates.

Divergent selection of KNR6 maximizes grain production by balancing the flowering-time adaptation and ear size in maize.

Divergent selection of KNR6 maximizes grain production by balancing the flowering-time adaptation and ear size in maize.

TasselLFANet: a novel lightweight multi-branch feature aggregation neural network for high-throughput image-based maize tassels detection and counting.

Accurately and rapidly counting the number of maize tassels is critical for maize breeding, management, and monitoring the growth stage of maize plants. With the advent of high-throughput phenotyping platforms and the availability of large-scale datasets, there is a pressing need to automate this task for genotype and phenotype analysis. Computer vision technology has been increasingly applied in plant science, offering a promising solution for automated monitoring of a large number of plants. However, the current state-of-the-art image algorithms are hindered by hardware limitations, which compromise the balance between algorithmic capacity, running speed, and overall performance, making it difficult to apply them in real-time sensing field environments. Thus, we propose a novel lightweight neural network, named TasselLFANet, with an efficient and powerful structure for accurately and efficiently detecting and counting maize tassels in high spatiotemporal image sequences. Our proposed approach improves the feature-learning ability of TasselLFANet by adopting a cross-stage fusion strategy that balances the variability of different layers. Additionally, TasselLFANet utilizes multiple receptive fields to capture diverse feature representations, and incorporates an innovative visual channel attention module to detect and capture features more flexibly and precisely. We conducted a series of comparative experiments on a new, highly informative dataset called MrMT, which demonstrate that TasselLFANet outperforms the latest batch of lightweight networks in terms of performance, flexibility, and adaptability, achieving an F1 measure value of 94.4%, a mAP.@5 value of 96.8%, and having only 6.0M parameters. Moreover, compared with the regression-based TasselNetV3-Seg† model, our proposed model achieves superior counting performance, with a mean absolute error (MAE) of 1.80, a root mean square error (RMSE) of 2.68, and a R2 of 0.99. The proposed model meets the accuracy and speed requirements of the vision system in maize tassel detection. Furthermore, our proposed method is reliable and unaffected by geographical changes, providing essential technical support for computerized counting in the field.

High responsiveness to nitrogen supply in modern maize cultivars is contributed to gibberellin-dependent leaf elongation

Modern maize cultivars have high nitrogen responsiveness of grain yield. However, the underlying physiological mechanism is unclear. In the present study, from 17 cultivars released from 1950 s to 2010 s in China, three maize cultivars released in 1950 s (BMY), 1970 s (ZD2), and 1990 s (ZD958) were selected according to their growth responses to nitrogen supply. Nitrogen responsiveness of shoot biomass was highest in the new cultivar ZD958, and the lowest in the old cultivar BMY, with the medium cultivar ZD2 in between. Shoot biomass was closely related to leaf elongation rate. Leaf elongation was further analyzed using kinematic analysis method. Cell division rate and cell production rate were greater and more responsive to nitrogen supply in ZD958 than in the other cultivars. In agreement, there were more cells in the elongation zone of ZD958 and they were more responsive to increasing supply, resulting a longer leaf elongation zone. The interaction effect between cultivar and nitrogen supply on leaf elongation was in consistence with the change in gibberellin (GA1 and GA3) concentration in leaf growth zone. Accordingly, the genes encoding gibberellin biosynthesis or signal transduction was more up-regulated in ZD958, which was positively correlated to the up-regulation of genes related to cell cycle and DNA replication. On the contrary, the genes related to the inactivation of gibberellin was more down-regulated in ZD958. Exogenous application of bioactive gibberellin or its biosynthesis inhibitor eliminated the interaction effect between cultivar and nitrogen supply on leaf elongation rate. In conclusion, modern maize breeding may have increased nitrogen responsiveness in maize by enhancing the gibberellins-dependent leaf elongation response to high nitrogen supply.

A New 5'-UTR <i>LcyE </i>allele Correlates with Increased Expression of the Lycopine-ε-Cyclase Gene Determining the Flow of the β-ε Branch of the Carotenoid Biosynthesis Pathway in Maize

The color of Zea mays L. kernel is determined by the content and composition of carotenoids, including provitamin A, which is a product of the β-β (β-carotene, β-cryptoxanthin) and β-ε (α-carotene) branches of carotenogenesis. The ratio of the fluxes of the branches depends on the activity of the lycopene-ε-cyclase LcyE, which determines the β-ɛ branch. In this work, we analyzed allelic variants of the LcyE gene, which are potentially effective for increasing the biosynthesis of β-carotene, in 20 maize inbred lines of domestic selection, which differ in grain color. The 5'-UTR region of the LcyE gene were amplified and sequenced. Fragment analysis showed the presence of allele “2” in four lines and a new allele “5” in 16 lines. The polymorphism of the new allele “5” was characterized – four mononucleotide polymorphisms and two deletions. The comparison of cis-regulatory elements in the analyzed region of the 5'-UTR of alleles “2” and “5” revealed a difference in binding sites with transcription factors. Expression of the LcyE gene was determined in the leaves of two lines with the allele “2” and three lines with the allele “5”. A direct relationship was shown between the presence of the allele “5” and a decrease in gene expression: the level of gene transcription in the case of the allele “2” was 10–15 times higher than in the case of the allele “5”. It has been suggested that the presence of allele “5” of the LcyE gene in the maize genome correlates with a decrease or suppression of the LcyE expression and, with stable activity of other carotenogenesis enzymes, with grain color. The use of allele “5” donors in combination with the known dark yellow or orange color of the grain can be used in the breeding of maize with increased synthesis of provitamin A in the grain.

GWAS across multiple environments and WGCNA suggest the involvement of ZmARF23 in embryonic callus induction from immature maize embryos.

Combined GWAS, WGCNA, and gene-based association studies identified the co-expression network and hub genes for maize EC induction. ZmARF23 bound to ZmSAUR15 promoter and regulated its expression, affecting EC induction. Embryonic callus (EC) induction in immature maize embryos shows high genotype dependence, which limits the application of genetic transformation in transgenic breeding and gene function elucidation in maize. Herein, we conducted a genome-wide association mapping (GWAS) for four EC induction-related traits, namely rate of embryonic callus induction (REC), increased callus diameter (ICD), ratio of shoot formation (RSF), and length of shoot (LS) across different environments. A total of 77 SNPs were significantly associated these traits under three environments and using the averages (across environments). Among these significant SNPs, five were simultaneously detected under multiple environments and 11 had respective phenotypic variation explained > 10%. A total of 257 genes were located in the linkage disequilibrium decay of these REC- and ICD-associated SNPs, of which 178 were responsive to EC induction. According to the expression values of the 178 genes, we performed a weighted gene co-expression network analysis (WGCNA) and revealed an EC induction-associated module and five hub genes. Hub gene-based association studies uncovered that the intragenic variations in GRMZM2G105473 and ZmARF23 influenced EC induction efficiency among different maize lines. Dual-luciferase reporter assay indicated that ZmARF23 bound to the promoter of a known causal gene (ZmSAUR15) for EC induction and positively regulated its expression on the transcription level. Our study will deepen the understanding of genetic and molecular mechanisms underlying EC induction and contribute to the use of genetic transformation in maize.

Assessment of the influence of soil inoculation on changes in the adaptability of maize hybrids

The aim of this paper is to present the results of the field trial carried out to collect and assess data on the interaction of maize (Zea mays L) genotypes and beneficial microorganisms. The small plot field trial consisting of untreated control plots and plots treated with biostimulants was conducted in three consecutive years (2019, 2020 and 2021). Yield is a particularly important trait from the aspect of maize breeding as well as maize production; therefore, the present study focused more closely on how it was influenced by the biostimulant treatments. The level of grain yield, grain moisture content at harvest and grain dry-matter content were observed and recorded as the components of yield. The nutritional value of kernels was also tested, and protein, oil and starch contents were analysed as the most important components of this trait. The results reflected that the treatment with biostimulants constituted from beneficial microorganisms can be listed among the factors influencing the grain yield, in addition to the seasonal effect, the genotype and the nutrient supply of the soil. The treatment with biostimulants, even on its own among the factors, had an impact on the quantity and components of yield, and on the characteristics determining the kernel nutritional value. The interaction between the genotypes and the interacting microorganisms is of specific importance. The most spectacular result was attained with the application of one of the biostimulants leading to elevated grain yield in 75% of the maize genotypes in the study, along with a kernel nutritive value equal to the control group over all of the three years of the trial.

Genome-Wide Association Study for Root Morphology and Phosphorus Acquisition Efficiency in Diverse Maize Panels.

Maximizing soil exploration through modifications of the root system is a strategy for plants to overcome phosphorus (P) deficiency. Genome-wide association with 561 tropical maize inbred lines from Embrapa and DTMA panels was undertaken for root morphology and P acquisition traits under low- and high-P concentrations, with 353,540 SNPs. P supply modified root morphology traits, biomass and P content in the global maize panel, but root length and root surface area changed differentially in Embrapa and DTMA panels. This suggests that different root plasticity mechanisms exist for maize adaptation to low-P conditions. A total of 87 SNPs were associated to phenotypic traits in both P conditions at -log10(p-value) ≥ 5, whereas only seven SNPs reached the Bonferroni significance. Among these SNPs, S9_137746077, which is located upstream of the gene GRMZM2G378852 that encodes a MAPKKK protein kinase, was significantly associated with total seedling dry weight, with the same allele increasing root length and root surface area under P deficiency. The C allele of S8_88600375, mapped within GRMZM2G044531 that encodes an AGC kinase, significantly enhanced root length under low P, positively affecting root surface area and seedling weight. The broad genetic diversity evaluated in this panel suggests that candidate genes and favorable alleles could be exploited to improve P efficiency in maize breeding programs of Africa and Latin America.

Genome-Wide Meta-Analysis of QTLs Associated with Root Traits and Implications for Maize Breeding.

Root system architecture (RSA), also known as root morphology, is critical in plant acquisition of soil resources, plant growth, and yield formation. Many QTLs associated with RSA or root traits in maize have been identified using several bi-parental populations, particularly in response to various environmental factors. In the present study, a meta-analysis of QTLs associated with root traits was performed in maize using 917 QTLs retrieved from 43 mapping studies published from 1998 to 2020. A total of 631 QTLs were projected onto a consensus map involving 19,714 markers, which led to the prediction of 68 meta-QTLs (MQTLs). Among these 68 MQTLs, 36 MQTLs were validated with the marker-trait associations available from previous genome-wide association studies for root traits. The use of comparative genomics approaches revealed several gene models conserved among the maize, sorghum, and rice genomes. Among the conserved genomic regions, the ortho-MQTL analysis uncovered 20 maize MQTLs syntenic to 27 rice MQTLs for root traits. Functional analysis of some high-confidence MQTL regions revealed 442 gene models, which were then subjected to in silico expression analysis, yielding 235 gene models with significant expression in various tissues. Furthermore, 16 known genes viz., DXS2, PHT, RTP1, TUA4, YUC3, YUC6, RTCS1, NSA1, EIN2, NHX1, CPPS4, BIGE1, RCP1, SKUS13, YUC5, and AW330564 associated with various root traits were present within or near the MQTL regions. These results could aid in QTL cloning and pyramiding in developing new maize varieties with specific root architecture for proper plant growth and development under optimum and abiotic stress conditions.

Genome‐wide association study for bacterial leaf streak resistance in maize

AbstractMaize (Zea mays L.), one of the most important crops worldwide, is affected by foliar diseases that limit its global production. Bacterial diseases have increased in Argentina during the last years. The aim of this work was to explore a maize panel provided by the International Maize and Wheat Improvement Center (CIMMYT) to identify alleles associated with resistance to bacterial leaf streak (BLS) of maize, a disease caused by Xanthomonas vasicola pv. vasculorum, in central Argentina. A diverse panel of 200 maize lines was evaluated for resistance to bacterial diseases in four environments of central Argentina in 2020 and 2021. The predictor of the genetic merit does not include environmental effects and 46,990 single‐nucleotide polymorphisms obtained by genotyping‐by‐sequencing were used in the genome‐wide association study (GWAS). The 10 lines with the lowest severity across environments belonged to different environmental adaptation programs defined by CIMMYT. The GWAS allowed us to identify 11 genomic regions associated with BLS, located in chromosomes 1, 2, 5, 7, 8, and 9. Five of those regions, located in bins 1.04, 2.01, 5.03, 8.06, and 9.03, were associated with plant defense candidate genes such as strictosidine synthase‐like 11, protein‐serine/threonine phosphatase, and a putative Leucine‐Rich repeats receptor‐like serine/threonine‐protein kinase gene. Our study provides potential resistance alleles to BLS that can be incorporated to improve maize breeding programs.

Evaluation of the growth and tolerance of maize lines under aluminum stress

Abstract. Herawati, Riadi M,MusaY, Efendi R, Azrai M. 2023. Evaluation of the growth and tolerance of maize lines under aluminum stress. Biodiversitas24: 1417-1430. Breeding and utilization of Al-tolerant maize are among the technological applications for preventing a decrease in the growth rate and grain yield of maize in suboptimal fields. This study aimed to determine the growth and production of maize lines under Al stress, obtain maize lines that are tolerant to Al stress, and determine Al absorption in the tested maize lines. This study comprised two steps. In the first step, maize lines were evaluated in acid soils with a pH of 5.12 and an Al saturation of around 22.13%, while the normal condition was carried out on soil with a pH of 6.60 and 0% Al saturation. The study was arranged in a randomized block with three replications. The maize lines used were 24 genotypes consisting of 20 maize lines and four elite lines as a check (Mal 03, CLYN 231, G102612, B11209). In the second step, maize lines were evaluated in the nutrient solution. This study was arranged in a split-plot design with three replications. The main plot was the concentration of Al at three levels, i.e., 0, 7, and 14 ppm. The subplot comprised seven maize lines representing sensitive, medium tolerant, and tolerant categories. They were Pop. A3-1, Pop. A7-1, CB.Pop 10-1-3-1-2-2, CB.Pop 15-4-2-1-1-1, CB.Pop 23-1-2-1-4-2, Mal 03, and G102612. These studies were conducted at the Indonesian Cereal Research Institute, Maros, South Sulawesi, Indonesia, from August 2021 to January 2022. This study showed that Al stress could reduce plant growth by around 10.84% to 50.51% and grain yield by around 62.23% compared to normal conditions. The traits that were significantly correlated with grain yield under Al stress (r>50%), which could be used in maize selection under Al stress, were the number of live plants, ear diameter, number of kernels per row, shelling percentage, SSI, crown Al absorption, and hematoxylin staining. There were two maize lines tolerant to Al stress, namely CB.Pop 11-2-3-4-2-1 and CB.Pop 15-4-2-1-1-1, with potential yields under Al stress conditions of 2.39 t ha-1and 1.59 t ha-1, respectively. Al absorption averages of roots and crowns of Al tolerant maize lines were 159.33 ppm and 36.33 ppm, respectively.

Pattern and variation in simple sequence repeat (SSR) at different genomic regions and its implications to maize evolution and breeding

BackgroundRepetitive DNA sequences accounts for over 80% of maize genome. Although simple sequence repeats (SSRs) account for only 0.03% of the genome, they have been widely used in maize genetic research and breeding as highly informative codominant DNA markers. The genome-wide distribution and polymorphism of SSRs are not well studied due to the lack of high-quality genome DNA sequence data.ResultsIn this study, using data from high-quality de novo-sequenced maize genomes of five representative maize inbred lines, we revealed that SSRs were more densely present in telomeric region than centromeric region, and were more abundant in genic sequences than intergenic sequences. On genic sequences, tri- and hexanucleotide motifs were more abundant in CDS sequence and some mono- and dinucleotide motifs were more abundant in UTR sequences. Median length and chromosomal density of SSRs were both narrowly range-bound, with median length of 14-18 bp and genome-wide average density of 3355.77 bp/Mbp. LTR-RTs of < 0.4 Mya had higher SSR density (4498-4992 bp/Mbp). The genome-specific and motif-specific SSR polymorphism were studied. Their potential breeding applications were discussed.ConclusionsWe found that the median length of SSR sequences of different SSR motifs was nearly constant. SSR density in genic regions was much higher than intergenic regions. In addition, SSR density at LTR-RTs of different evolutionary ages varied in a narrow range. The SSRs and their LTR-RT carriers evolved at an equal rate. All these observations indicated that SSR length and density were under control of yet unknown evolutionary forces. The chromosome region-specific and motif-specific SSR polymorphisms we observed supported the notion that SSR polymorphism was invaluable genome resource for developing highly informative genome and gene markers in maize genetic research and molecular breeding.

New Genes Identified as Modulating Salt Tolerance in Maize Seedlings Using the Combination of Transcriptome Analysis and BSA

(1) Background: Salt stress is an abiotic factor that limits maize yield and quality. A highly salt-tolerance inbred AS5 and a salt-sensitive inbred NX420 collected from Ningxia Province, China, were used to identify new genes for modulating salt resistance in maize. (2) Methods: To understand the different molecular bases of salt tolerance in AS5 and NX420, we performed BSA-seq using an F2 population for two extreme bulks derived from the cross between AS5 and NX420. Transcriptomic analysis was also conducted for AS5 and NX420 at the seedling stage after treatment with 150 mM of NaCl for 14 days. (3) Results: AS5 had a higher biomass and lower Na+ content than NX420 in the seedling stage after treatment with 150 mM NaCl for 14 days. One hundred and six candidate regions for salt tolerance were mapped on all of the chromosomes through BSA-seq using F2 in an extreme population. Based on the polymorphisms identified between both parents, we detected 77 genes. A large number of differentially expressed genes (DEGs) at the seedling stage under salt stress between these two inbred lines were detected using transcriptome sequencing. GO analysis indicated that 925 and 686 genes were significantly enriched in the integral component of the membrane of AS5 and NX420, respectively. Among these results, two and four DEGs were identified as overlapping in these two inbred lines using BSA-seq and transcriptomic analysis, respectively. Two genes (Zm00001d053925 and Zm00001d037181) were detected in both AS5 and NX420; the transcription level of Zm00001d053925 was induced to be significantly higher in AS5 than in NX420 (41.99 times versus 6.06 times after 150 mM of NaCl treatment for 48 h), while the expression of Zm00001d037181 showed no significant difference upon salt treatment in both lines. The functional annotation of the new candidate genes showed that it was an unknown function protein. (4) Conclusions: Zm00001d053925 is a new functional gene responding to salt stress in the seedling stage, which provides an important genetic resource for salt-tolerant maize breeding.

Genome-Wide Association Analysis Identified Newly Natural Variation for Photosynthesis-Related Traits in a Large Maize Panel

High-yielding cultivars with high water use efficiency are a main target in maize breeding; yet, no comprehensive study about the genetic regulation of photosynthesis, or about the ranges of variability for gas exchange-related parameters in maize has been published. Here, a large maize panel of 731 inbred lines previously genotyped was evaluated to elucidate the genetic basis of photosynthesis-related parameters, measured 15–30 days after silking, across three years. Large phenotypic and genotypic variations were observed in this panel with dramatic fluctuations in heritability for various traits. We detected 27 minor Quantitative Trait Loci (QTL), comprising 39 significant trait-Single Nucleotide Polymorphisms (SNPs), located mostly on chromosomes 5 and 8. Most candidates genes were novel, though a few of them were functionally associated with the theory of source-to-sink translocation presented in previous studies. Genomic selection of favorable alleles to enhance photosynthesis, along with other tools, could be a practical, and a promising, approach in the future. Leaf net photosynthesis and stomatal conductance are the most promising targets for breeding programs. We did not find any marker associated with intrinsic water use efficiency, which highlights that developing maize cultivars with more efficient use of water by genomic selection is not straightforward; however, given the high heritability value for this trait, phenotypic selection could be implemented.

Combining ability estimates for quality and non-quality protein maize inbred lines for grain yield, agronomic, and quality traits

IntroductionBiofortified maize varieties could contribute to the fight against hunger and malnutrition of the increasing human population and help meet the high demand of maize for human consumption, industrial use and feed for animal and poultry. The understanding of the genetic mechanisms conditioning the inheritance of grain yield and other agronomic and quality traits is essential in the development of superior maize genotypes. The main objective of this study was to determine the combining ability for grain yield and other agronomic traits of QPM and non-QPM inbred lines crossed with two QPM and two non-QPM testers.Materials and methodsA total of 130 hybrids were obtained by crossing 10 non-QPM and 23 QPM lines with four elite testers (two QPM and two non-QPM). The 130 single cross hybrids were evaluated at 13 sites in 2018 and 2019.Results and discussionThe results showed significant general combining ability (GCA) for lines and testers as well as significant specific combining ability (SCA) for hybrids for most of the measured traits. Non-additive gene action controlled the inheritance of grain yield while agronomic and quality traits were controlled by additive gene action. QPM lines 11, 14 and 28 and non-QPM tester CML444 showed desirable GCA effects for grain yield, indicating that these lines in combination with tester CML444 should be considered when targeting development of superior maize genotypes with QPM traits.ConclusionsBased on the SCA values, crosses 120, 108, 105, 99, 85, and 41 were identified as the best hybrids across the locations. It is recommended that maize breeding programs targeting the development of high yielding QPM hybrids should exploit QPM lines with high GCA values for heterosis to be realized. In addition, the identified superior hybrids may be further evaluated and consequently promoted for commercial release which could increase incomes of farmers and help to alleviate poverty, hunger and malnutrition in southern Africa and sub-Saharan Africa at large.

Assessment of Inbred Lines of Field Corn for Yield And Yield Attributes Through Line × Tester Method

A line × tester analysis comprising forty eight test-crosses generated by crossing 24 S3 inbred lines derived from commercial maize hybrid 981 with two testers. Heterosis study of these crosses against two standard checks was evaluated at Bangladesh Agricultural Research Institute, Gazipur during rabi 2015-16. The objectives of the study were to estimate general and specific combining ability effects of the inbred lines and to assess the test cross performance and estimate the amount of standard-heterosis of the hybrids for grain yield and yield related characters. Highly significant genotypic differences were observed indicated wide range of variability present among them. Five lines viz. Line 11, Line 14, Line 17, Line 24 and Line 30 were good general combiner for grain yield and possessed high means. Nine crosses showed (Line 18 × BIL22, Line 23 × BIL22, Line 27 × BIL22, Line 7 × BIL28, Line11 × BIL28, Line14 × BIL28, Line 24 × BIL28, Line 25 × BIL28 and Line 30 × BIL28) significant and positive specific combining ability effect for grain yield. The information on the nature of gene action with respective variety and characters might be used depending on the breeding objectives. These crosses, Line 24× BIL28 (11.40 t/ha), Line 18 × BIL22 (11.30 t/ha) and Line 25 × BIL28 (11.20 t/ha) showed higher yield, could be utilized in maize breeding activities. Estimation of heterosis was carried out using two commercial hybrids BARI Hybrid Maize-9 (BHM-9) and NK-40. The percent heterosis for grain yield varied from -23.39 to 4.6% against BHM-9. Among the 48 crosses, 13 crosses exhibited significant positive heterosis for grain yield.&#x0D; Bangladesh J. Agril. Res. 46(4): 469-489, December 2021

Training set designs for prediction of yield and moisture of maize test cross hybrids with unreplicated trials.

Unreplicated field trials and genomic prediction are both used to enhance the efficiency in early selection stages of a hybrid maize breeding program. No results are available on the optimal experimental design when combining both approaches. Our objectives were to investigate the effect of the training set design on the accuracy of genomic prediction in unreplicated maize test crosses. We carried out a cross validation study on basis of an experimental data set consisting of 1436 hybrids evaluated for yield and moisture for which genotyping information of 461 SNP markers were available. Training set designs of different size, implementing within environment prediction, within year prediction, across year prediction, and combinations of data sources across years and environments were compared with respect to their prediction accuracy. Across year prediction did not reach prediction accuracies that are useful for genomic selection. Within year prediction across environments provided useful correlations between observed and predicted breeding values. The prediction accuracies did not improve when adding to the training set data from previous years. We conclude that using all data available from unreplicated tests of the current breeding cycle provides a good accuracy of predicting test crosses, whereas adding data from previous breeding cycles, in which the genotypes are less related to the tested material, has only limited value for increasing the prediction accuracy.

Evaluation of source material for sweet maize by the main breeding characteristics

Topicality. The sweet maize grain differs from other maize subspecies in its high sugar content: the grain accumulates 2 times more mono- and disaccharides, 20 times more dextrins, and almost 2 times less starch, with a crude protein content of 10.4–14.9 %. The main direction of sweet maize breeding is to develop the high-yielding interline hybrids that are suitable for mechanized harvesting of cobs, and resistant to main diseases and pests, as well as characterized by high technological grain qualities. To effectively solve these challenges, it is necessary to know the morphological and biological characteristics and properly select the source material (self-pollinated lines). Purpose. To study of morphological and biological characteristics of sweet maize lines. Materials and methods. Visual phenological observations; laboratory-field method was used to determine morpho-biological characteristics of plants; measuring and weighing method – to determine yield and metric characteristics of plants; mathematical and statistical method - to determinate validity of results, variability of traits, correlational dependence of traits; analysis of variance; comprehensive assessment of morpho-biological and economically valuable characteristics of inbred lines. Results. According to analysis of sugar composition, the studied samples revealed a high content of monosaccharides (glucose, fructose, etc.) in the lines HOL-1 1411111, HOL-1 1411211, DKS346 114, DINAR346 141, HOL-19 and disaccharides (sucrose, lactose, maltose) in HOL-1 1411211, SVAN1212 123, HOL-19. These indicators are important in the deep processing of sweet maize for the food industry an individual product and as one of the components in the culinary products. These mono- and disaccharides are used to produce sweets, sweet or alcoholic drinks and sauces. The following DINAR346 141, HOL-1 1411511 lines had a low level of sucrose content: 3.7 and 4.6 %, respectively. Conclusions. According to the results of research on the breeding material of sweet maize, it was identified the self-pollinated families with high taste qualities (7 points), such as HOL-1 1411111, HOL-1 1411211, DKS346 114, HOL-4 1411141 and HOL-19, which will be involved to develop competitive high-yielding hybrids with a high sugar content in grain, increased taste and technological qualities in the sweet maize breeding programs in the future. Key words: sweet corn, line, sugar content, seed productivity, grain taste

Employing factor analytic tools for selecting high‐performance and stable tropical maize hybrids

AbstractGenotype‐by‐environment interaction (GEI) is a major concern in tropical maize breeding. Here, we used factor analytic mixed models (FAMM) to study GEI in a tropical maize dataset. Our goal was to select high‐performance and stable hybrids using factor analytic selection tools (FAST) derived from FAMM outputs. Because the dataset comprised two different planting seasons, we also investigated differences in the genetic gains between seasonal and general selection (i.e., for both seasons simultaneously). The trials were installed in a lattice design with 36 hybrids containing two replicates and blocks with six plants each. We evaluated 53 hybrids and seven checks in 48 environments, represented by a combination of locations, years and seasons. We fitted the FAMMs with distinct sets of factors. The best‐fitted FAMM was selected considering a parsimony‐explained variance balance. Using the best FAMM for both seasonal and general analyses, we estimated the following selection tools: overall performance (); root mean square deviation (), which represents general stability; and responsiveness , which represents specific stability. We selected hybrids based on an index built with and . Five and three hybrids were selected considering both general and seasonal analyses for the first and second season, respectively. Two hybrids were amongst the top eight for both seasonal analyses (i.e., only first season and only second season simultaenously). Higher genetic gains may be obtained by employing FAMM and using FAST in each season rather than analysing both seasons in a joint fashion.

EVALUACIÓN DE DAÑO POR Spodoptera frugiperda (J.E. SMITH) (LEPIDOPTERA: NOCTUIDAE) Y CARACTERIZACIÓN DE LOS RASGOS MORFOLÓGICOS FOLIARES EN POBLACIONES CRIOLLAS DE MAÍZ (Zea mays L.)

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; The fall armyworm &lt;em&gt;Spodoptera frugiperda &lt;/em&gt;is one of the most damaging pests of maize in tropical areas. &lt;strong&gt;Objective.&lt;/strong&gt; To evaluate the damage caused by &lt;em&gt;S. frugiperda&lt;/em&gt; and the leaf morphological traits in 15 populations of maize landrace. &lt;strong&gt;Methodology.&lt;/strong&gt; The leaf damage caused by &lt;em&gt;S. frugiperda&lt;/em&gt; and four-leaf morphological traits (leaf blade thickness, leaf blade hardness, specific leaf area and trichome density) were evaluated at 20, 30 and 40 days after emergence (DAE) in two seasons, dry (March and April) and rainy (June and July). Spearman correlation between the degree of leaf damage and each leaf morphological trait was also evaluated. &lt;strong&gt;Results.&lt;/strong&gt; Maize populations showed differential response to the damage caused by &lt;em&gt;S. frugiperda&lt;/em&gt; among seasons and evaluating date. The leaf morphological traits were different between seasons and among evaluating dates. The trichome density had intermediate negative correlation with the level of leaf damage in rainy season (&lt;em&gt;r&lt;sub&gt;s&lt;/sub&gt;&lt;/em&gt; = − 0.32,&lt;em&gt; p&lt;/em&gt; &amp;lt; 0.001). &lt;strong&gt;Implications.&lt;/strong&gt; The lower leaf damage may be indicator of resistance against &lt;em&gt;S. frugiperda&lt;/em&gt;. &lt;strong&gt;Conclusion.&lt;/strong&gt; The population 2020−M62 had low susceptibility to &lt;em&gt;S. frugiperda&lt;/em&gt;, this population may be candidate for maize breeding program.&lt;/p&gt;