Maize Breeding Research Articles

QTG-Miner aids rapid dissection of the genetic base of tassel branch number in maize

Genetic dissection of agronomic traits is important for crop improvement and global food security. Phenotypic variation of tassel branch number (TBN), a major breeding target, is controlled by many quantitative trait loci (QTLs). The lack of large-scale QTL cloning methodology constrains the systematic dissection of TBN, which hinders modern maize breeding. Here, we devise QTG-Miner, a multi-omics data-based technique for large-scale and rapid cloning of quantitative trait genes (QTGs) in maize. Using QTG-Miner, we clone and verify seven genes underlying seven TBN QTLs. Compared to conventional methods, QTG-Miner performs well for both major- and minor-effect TBN QTLs. Selection analysis indicates that a substantial number of genes and network modules have been subjected to selection during maize improvement. Selection signatures are significantly enriched in multiple biological pathways between female heterotic groups and male heterotic groups. In summary, QTG-Miner provides a large-scale approach for rapid cloning of QTGs in crops and dissects the genetic base of TBN for further maize breeding.

Creation of doubled haploid lines of maize <i>Zea mays</i> L. by resynthesis from a tetraploid population

The search for new, effective methods for broadening the genetic polymorphism of the original breeding material remains one of important problems of hybrid maize breeding. Globally, breeding of commercial maize varieties and hybrids is carried out using diploid genotypes, whereas tetraploid sources of initial material and wild relatives of maize are poorly involved in the breeding process. The direct heteroploid crosses between diploid and tetraploid genotypes lead to the formation of weakly fertile or completely sterile triploid hybrids, which are cytologically unstable in subsequent generations. Tetraploid maize (2n=40), as well as some wild relatives with tetraploid genome, such as Zea perennis Hitchk. (2n=40) and Tripsacum dactiloides (L.) L. (2n=72), are attractive to breeders as sources for improving economically valuable traits. The attractiveness of resynthesized diploid lines is explained by the fact that unequal crossing over between homologous chromosomes forming polyvalent associations of chromosomes, more chromosomal rearrangements occur in tetraploids than in diploid genotypes, the chromosomes of which form bivalents. Synthetic tetraploid populations of maize and its tetraploid wild relatives have great potential of variability for improving diploid maize. The authors proposed a direct method for the resynthesis of doubled haploid lines using haploid induction and an indirect method for obtaining diploid lines by heteroploid crossing and subsequent segregation of a triploid hybrid in the progeny. The method of resynthesizing the tetraploid maize genome to diploid serves as an ideal model for studying the processes of crossing over in meiosis between multivalent associations of homologous chromosomes; it is promising for obtaining diploid lines with an increased frequency of recombination between the homologous chromosomes of different genomes, combined into a common one, and can serve as a source for obtaining aneuploid series.

Genome-wide association study of maize resistance to Pythium aristosporum stalk rot.

Stalk rot, a severe and widespread soil-borne disease in maize, globally reduces yield and quality. Recent documentation reveals that Pythium aristosporum has emerged as one of the dominant causal agents of maize stalk rot. However, a previous study of maize stalk rot disease resistance mechanisms and breeding had mainly focused on other pathogens, neglecting P. aristosporum. To mitigate crop loss, resistance breeding is the most economical and effective strategy against this disease. This study involved characterizing resistance in 295 inbred lines using the drilling inoculation method and genotyping them via sequencing. By combining with population structure, disease resistance phenotype, and genome-wide association study (GWAS), we identified 39 significant single-nucleotide polymorphisms (SNPs) associated with P. aristosporum stalk rot resistance by utilizing six statistical methods. Bioinformatics analysis of these SNPs revealed 69 potential resistance genes, among which Zm00001d051313 was finally evaluated for its roles in host defense response to P. aristosporum infection. Through virus-induced gene silencing (VIGS) verification and physiological index determination, we found that transient silencing of Zm00001d051313 promoted P. aristosporum infection, indicating a positive regulatory role of this gene in maize's antifungal defense mechanism. Therefore, these findings will help advance our current understanding of the underlying mechanisms of maize defense to Pythium stalk rot.

Natural polymorphisms in ZmIRX15A affect water-use efficiency by modulating stomatal density in maize.

Stomatal density (SD) is closely related to crop drought resistance. Understanding the genetic basis for natural variation in SD may facilitate efforts to improve water-use efficiency. Here, we report a genome-wide association study for SD in maize seedlings, which identified 18 genetic variants that could be resolved to seven candidate genes. A 3-bp insertion variant (InDel1089) in the last exon of Zea mays (Zm) IRX15A (Irregular xylem 15A) had the most significant association with SD and modulated the translation of ZmIRX15A mRNA by affecting its secondary structure. Dysfunction of ZmIRX15A increased SD, leading to an increase in the transpiration rate and CO2 assimilation efficiency. ZmIRX15A encodes a xylan deposition enzyme and its disruption significantly decreased xylan abundance in secondary cell wall composition. Transcriptome analysis revealed a substantial alteration of the expression of genes involved in stomatal complex morphogenesis and drought response in the loss-of-function of ZmIRX15A mutant. Overall, our study provides important genetic insights into the natural variation of leaf SD in maize, and the identified loci or genes can serve as direct targets for enhancing drought resistance in molecular-assisted maize breeding.

Gene action and inheritance of grain yield and root morphological traits in hybrid maize grown under water deficit conditions

Evaluation of various root traits and determination of their genetic control in response to water deficit stress is crucial for improving and stabilizing grain yield worldwide. The present study aimed at evaluating the gene action, heritability and genetic variances of grain yield and root morphological traits under water deficit conditions in mature maize. Seeds of seven maize genotypes, including B73 (maternal inbred line), MO17 (paternal inbred line), F1 (SC704), F2, BC1, BC2 and F3 were sown in PVC tubes and grown under field water capacity. The maize plants were then subjected to three water regimes of 100% FC, 55% and 75% available water depletion at 5–6 leaf stage and continued to silk emergence in 2018 and 2019 (two years). The generation mean analysis results revealed that non-additive effects were greater than the additive effects. A high narrow sense heritability and additive variance were found for root dry weight and seminal root number, suggesting that selection in the parents’ inbred lines or early segregating generations could be an efficient method for genetic improvement of the traits under deficit irrigation conditions. Contrarily, selection for grain yield, root volume, primary root length, root surface area, root diameter and root fresh weight should be delayed for several generations until a high level of gene fixation is attained. Based on correlation analysis and percent change of the studied traits under deficit irrigation conditions, SC704 and MO17 could be used as a source for water deficit tolerance in maize breeding programs. Overall, the results suggested that the selection of root traits linked to better plant growth has great potential to alleviate water deficit stress, contributing to sustainable maize production in drought-prone areas.

Reciprocal testcross design for genome-wide prediction of maize single-cross performance.

A reciprocal testcross design increases the relatedness among single crosses and testcrosses, thereby increasing the effectiveness of genome-wide prediction in maize. A reciprocal testcross design uses parental inbreds in an opposite heterotic group as testers in maize (Zea mays L.) inbred development. In particular, doubled haploids from the A × B cross are testcrossed with inbreds Y and Z, and doubled haploids from Y × Z are testcrossed with inbreds A and B. Our objective was to determine if a reciprocal testcross design is superior to a traditional, non-reciprocal testcross design. A total of 700 Iowa Stiff Stalk Synthetic (BSSS) doubled haploids and 231 non-BSSS doubled haploids were developed from 10 breeding populations and had data on 11,032 single nucleotide polymorphism markers. Each doubled haploid was testcrossed to one to five testers from the opposite heterotic group, and the resulting 1642 testcrosses were evaluated in multilocation yield trials in 2019. Divergent selection for yield/moisture, on the basis of genome-wide predictions according to a reciprocal testcross design, led to significant responses (in 2020) in all 10 populations for yield/moisture and moisture and in three populations for yield. Predictive ability for yield/moisture and moisture was 0.11 to 0.26 higher with a reciprocal testcross design than with a testcross design. This higher predictive ability was attributed to a stronger relatedness between the training and test populations. No significant difference in predictive ability was found for yield, for which predictive ability was lower. Differences among genetic models that included and excluded specific combining ability were small. Overall, the empirical results supported the usefulness of a reciprocal testcross design in maize breeding.

Biochemical Characterization of Parental Inbred Lines and Hybrids of Maize (Zea mays L.) under Different Irrigation Conditions

Maize (Zea mays L.) is a significant crop with extensive agricultural and economic importance worldwide. With increasing concerns over water scarcity and climate change, understanding the responses of maize plants under water stress conditions is crucial to develop drought-tolerant cultivar (s). In present investigation, alteration in different biochemical parameters, including chlorophyll content, malondialdehyde (MDA) levels, hydrogen peroxide (H2O2) content, peroxidase, glutathione reductase (GR), and catalase activities, among 12 parental inbred lines along with 66 hybrids and two checks under irrigated and partial irrigated conditions were examined. Under irrigated conditions, the chlorophyll content was highest in the parental inbred line IL8, intimately followed by IL6, while IL5 exhibited the lowest content. MDA levels were significantly higher in the parental line IL8 and hybrid IL1 × IL6, whereas IL5 and IL3 × IL11 exhibited the lowest levels. H2O2 content was found to be highest in the parental line IL5 and hybrid IL8 × IL12, whereas IL4 and IL2 × IL5 displaying the lowest levels. Peroxidase activity was highest in IL7 and hybrid IL1 × IL7, whilst IL6 and IL4 × IL7 showed the lowest activity. Glutathione reductase activity was found highest in IL1 and IL9 × IL12, whereas IL6 and hybrid IL1 × IL3 exhibited the lowest activity. Catalase activity was highest in IL8 and IL2 × IL10, while IL4 and IL2 × IL6 displayed the lowest activity under irrigated conditions. Under partial irrigated conditions, almost similar trends were documented for the most of parameters, with slight variations in the expression levels. Notably, the drought-tolerant genotypes demonstrated higher chlorophyll content, peroxidase, glutathione reductase, and catalase activities, while drought-sensitive genotypes unveiled elevated MDA levels and H2O2 content. Phylogenetic analysis revealed five major clusters, indicating significant variability in different biochemical profiles among the genotypes. The heat map analysis supported the identification of distinct expression patterns of biochemical parameters, contributing to our understanding of the genotypic responses to varying irrigation conditions. These findings provide valuable insights for maize breeding programmes aimed to breed drought-tolerant cultivar (s) with enhanced antioxidant defences and stress tolerance.

Phenotypic and Genotypic Diversity of Puccinia sorghi in Eastern Australia: Implications for Maize Breeding Programs

Common rust of maize (CR), caused by Puccinia sorghi Schwein., is found in all maize growing regions across the globe. In recent years, an increase in the incidence and severity of CR has been observed in Australia. The challenges posed by a diverse population of P. sorghi to maize breeding programs and the strategies required to deploy durable resistance were explored. Preliminary studies of diversity were conducted by phenotyping the five most diverse isolates against maize lines carrying no resistance genes and one to four resistance genes. The results showed that further genotyping studies were required. Short reads of 17 CR isolates were collected from an array of agroecological regions in Eastern Australia, and these were mapped back against the hybrid assembly of Isolate 1. A hybrid assembly between short (Illumina paired-end) and long (PacBio) reads was conducted in MaSuRCA of the first isolate collected. A draft genome of 145,963,792 bp was obtained after QUAST analysis, with a total length of 145,815,044 bp (when removing base pairs below ≥1,000). The prediction from the BRAKER pipeline identified 20,438 gene models. All 17 isolates sequenced represented unique genotypes, and no clones were detected. The 17 isolates grouped into three clusters. The diversity observed within the population of P. sorghi in Australia suggests that monogenic resistance might not be durable. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Yellow maize breeding for higher beta-carotene: farmers’ perceptions of Vitamin-A deficiency consequences and readiness to grow improved varieties in Ghana

Vitamin A deficiency poses serious health concerns among the Ghanaian populace, particularly children and pregnant women. The production and consumption of yellow maize, which contains pro-vitamin A carotenoids such as beta carotene, is therefore encouraged. Consequently, yellow maize consumption is fast gaining acceptance. However, in the near future comensurate increases in production must be achieved to ensure food security. In this regard, the aims of the study were to: evaluate farmer willingness to cultivate yellow maize varieties with enhanced beta carotene content, ascertain extent of farmers’ knowledge on production constraints and mitigation, and evaluate farmers’ perception on nutritional benefits of yellow maize and the effects of vitamin A deficiency. The survey was conducted between January and May 2018 and it covered four districts representing the forest and guinea savanna ecological zones in Ghana. In each district, five communities with 10 participants each were covered. Most yellow maize farmers (78 %) were between 15 and 55 years, 42.5 % of the farmers had no formal education, 29 % had secondary education and only 8 % had tertiary education. The main challenges facing yellow maize (YM) farmers were pest control and low yield due to erratic rainfall. Majority (70 %) of the farmers had heard about vitamin A deficiency and also noticed stunted growth, mental retardation and poor eye sight in their communities but did not link such symptoms to vitamin A deficiency. Most respondents (70 %) were not aware that yellow maize contains beta carotene. Majority (70 %) of the respondents opined that improvement in the beta carotene content of yellow maize will greatly help to drastically minimize vitamin A deficiency and enhance food security. The information elicited from farmers will guide future development of yellow maize varieties for improved production and nutrition. Key words: maize, vitamin-A, deficiency, beta-carotene, food security, improved variety

Unraveling Prevalence and Effects of Deleterious Mutations in Maize Elite Lines across Decades of Modern Breeding.

Future breeding is likely to involve the detection and removal of deleterious alleles, which are mutations that negatively affect crop fitness. However, little is known about the prevalence of such mutations and their effects on phenotypic traits in the context of modern crop breeding. To address this, we examined the number and frequency of deleterious mutations in 350 elite maize inbred lines developed over the past few decades in China and the United States. Our findings reveal an accumulation of weakly deleterious mutations and a decrease in strongly deleterious mutations, indicating the dominant effects of genetic drift and purifying selection for the two types of mutations, respectively. We also discovered that slightly deleterious mutations, when at lower frequencies, were more likely to be heterozygous in the developed hybrids. This is consistent with complementation as a potential explanation for heterosis. Subsequently, we found that deleterious mutations accounted for more of the variation in phenotypic traits than nondeleterious mutations with matched minor allele frequencies, especially for traits related to leaf angle and flowering time. Moreover, we detected fewer deleterious mutations in the promoter and gene body regions of differentially expressed genes across breeding eras than in nondifferentially expressed genes. Overall, our results provide a comprehensive assessment of the prevalence and impact of deleterious mutations in modern maize breeding and establish a useful baseline for future maize improvement efforts.

A gibberellin-deficient maize mutant exhibits altered plant height, stem strength and drought tolerance.

The reduction in endogenous gibberellin improved drought resistance, but decreased cellulose and lignin contents, which made the mutant prone to lodging. It is well known that gibberellin (GA) is a hormone that plays a vital role in plant growth and development. In recent years, a growing number of studies have found that gibberellin plays an important role in regulating the plant height, stem length, and stressed growth surfaces. In this study, a dwarf maize mutant was screened from an EMS-induced mutant library of maize B73. The mutated gene was identified as KS, which encodes an ent-kaurene synthase (KS) enzyme functioning in the early biosynthesis of GA. The mutant was named as ks3-1. A significant decrease in endogenous GA levels was verified in ks3-1. A significantly decreased stem strength of ks3-1, compared with that of wild-type B73, was found. Significant decreases in the cellulose and lignin contents, as well as the number of epidermal cell layers, were further characterized in ks3-1. The expression levels of genes responsible for cellulose and lignin biosynthesis were induced by exogenous GA treatment. Under drought stress conditions, the survival rate of ks3-1 was significantly higher than that of the wild-type B73. The survival rates of both wild-type B73 and ks3-1 decreased significantly after exogenous GA treatment. In conclusion, we summarized that a decreased level of GA in ks3-1 caused a decreased plant height, a decreased stem strength as a result of cell wall defects, and an increased drought tolerance. Our results shed light on the importance of GA and GA-defective mutants in the genetic improvement of maize and breeding maize varieties.

Genetic structure analysis and identifying key founder inbred lines in diverse elite sub-tropical maize inbred lines

Understanding the genetic relationships between the key founder inbred lines and derived inbred lines could provide insight into the breeding history and the structure of genetic diversity of the available elite inbred lines with desirable target traits. The maize improvement program at the International Institute of Tropical Agriculture (IITA) analyzed the pedigree information of 623 sub-tropical maize inbred lines generated at the IITA maize breeding program to identify the key founder inbred lines. We also used 5032 SNP markers to assess the genetic similarities of the founder inbred lines with their progenies subsequently developed for specific target traits. The results of pedigree analysis and SNP markers-based similarity scores identified 20 key founder inbred lines with significant contributions to the development of drought tolerant, early maturing, productive, Striga resistant, provitamin A enriched, and quality protein maize inbred lines. In our breeding program, line TZMi501 belonging to a flint heterotic group (HGA), and TZMi407-S and TZMi214, representing the dent heterotic group (HGB), were identified as the most useful founder inbred lines. The 623 inbred lines were consistently separated into four clusters based on Ward’s hierarchical clustering, structure, and principal component analyses, with the 20 founder inbred lines spread into all clusters. The founder inbred lines were more genetically related to the productive inbred lines but showed genetic divergence from the provitamin A enriched inbred lines. These results provide a better understanding of the breeding history of the sub-tropical maize inbred lines to facilitate parental selection aligned to existing heterotic groups for use in breeding programs targeting the improvement of essential traits in maize.

DeepMaizeNet: A novel hybrid approach based on CBAM for implementing the doubled haploid technique

AbstractMaize (Zea mays L.) is an important cereal plant in the family of wheatgrass cultivated all over the world. With the increase in human population and environmental factors, the need for maize plants is increasing day by day. One of the efficient methods of increasing production of the maize is maize breeding. The most effective and rapid method for maize breeding is the doubled haploid (DH) technique. This technique reduces maize breeding time and increases productivity. There are different selection methods to select haploid maize seeds in the maize breeding process. Among these selection methods, the most common and most successful selection method is the visual checking of the R1‐Navajo marker. Maize seed separation by hand is a time‐consuming and error‐prone operation. It is labor‐intensive and very tiring; therefore, it is essential to develop a fast and highly accurate intelligent system that separates diploid and haploid maize seeds from each other. This study presents a pioneering approach, introducing the DeepMaizeNet, a hybrid deep learning model that showcases its prowess in accurately classifying haploid maize seeds. The classification of haploid seeds holds significant value for the DH technique, and the proposed model's success is a promising step toward enhanced efficiency. The proposed hybrid model exploits some new techniques such as convolution block attention module, hypercolumn, 2D upsampling, and residual block. For the assessment of the proposed model, the five‐fold cross‐validation technique is employed. The result shows that DeepMaizeNet provides a promising performance by achieving 94.13% accuracy, 94.91% F1‐score, and 97.27% sensitivity.

Maize kernel metabolome involved in resistance to fusarium ear rot and fumonisin contamination.

Fusarium verticillioides poses a threat to worldwide maize production due to its ability to infect maize kernel and synthesize fumonisins that can be accumulated above safety levels for humans and animals. Maize breeding has been proposed as key tool to decrease kernel contamination with fumonisins, but metabolic studies complementary to genomic approaches are necessary to disclose the complexity of maize resistance. An untargeted metabolomic study was proposed using inbreds genetically related but with contrasting levels of resistance in order to uncover pathways implicated in resistance to Fusarium ear rot (FER) and fumonisin contamination in the maize kernel and to look for possible biomarkers. Metabolite determinations were performed in kernels collected at 3 and 10 days after inoculation with F. verticillioides (dat). Discriminant metabolites between resistant and susceptible RILs were rather found at 10 than 3 dat, although metabolite differences at later stages of colonization could be driven by subtle variations at earlier stages of infection. Within this context, differences for membrane lipid homeostasis, methionine metabolism, and indolacetic acid conjugation seemed highly relevant to distinguish between resistant and susceptible inbreds, confirming the polygenic nature of resistance to FER and fumonisin contamination in the maize kernels. Nevertheless, some specific metabolites such as the polyamine spermidine and/or the alkaloid isoquinoline seemed to be promising indirect selection traits to improve resistance to FER and reduce fumonisin accumulation. Therefore, in vitro and in vivo experiments will be necessary to validate the inhibitory effects of these compounds on fumonisins biosynthesis.

A practical method to improve the efficiency of pollination in maize breeding and genetics research

AbstractSeed increase through manual pollination is a critical part of maize breeding and genetics research to advance generations in breeding programs, to create desired research crosses, and produce hybrid seed for trials. Pollination in the field and in controlled environments relies on the availability of high‐quality pollen at the time that recipient silks are receptive. Generally, pollinations are made by capturing pollen from the tassel in a paper pollinating bag placed on the tassels one day prior to pollination and newly released pollen is then transferred to silks on the target plant. In the field, maize pollen is only viable for one to four hours following dehiscence and the rate of desiccation is influenced by environmental conditions. We have developed a method which increases the lifespan of pollen and allows pollen from a single tassel to be used to pollinate many ears by mixing fresh pollen with a dilutant that can be stored for multiple days. We identified characteristics of the size of suitable substrates and selected a PEEK‐based substrate for regular utilization. We evaluated pollen viability and empirically demonstrated the capability to store pollen up to 9 days when pollen is mixed with a PEEK substrate and stored at 6°C. The pollen storage method was used to make successful pollinations across 24 maize inbred lines tested and was generally equivalent to the standard manual pollination process. This method has the potential to increase the efficiency of breeding operations and may be useful in an array of genetic studies.

Accelerated leaf appearance and flowering in maize after four decades of commercial breeding

AbstractMaize breeding programs have indirectly altered many plant traits; however, our knowledge of some important phenological traits remains unexplored. One such trait is leaf appearance rate, which is crucial for predicting maize development. We studied 40 short‐season (103‐day) and 38 long‐season (111‐day) hybrids released from 1980 to 2020 by Bayer Crop Science. Measurements included weekly counting of collared leaves across 13 experiments in the US Corn Belt. The progression of leaf number was expressed as a function of thermal time and described with a trilinear model. Results indicated that new 111‐day hybrids produce leaves faster than old hybrids throughout the vegetative phase (7.4% and 3.1% faster before and after the ninth leaf stage, respectively), whereas new 103‐day hybrids produce leaves faster only after the ninth leaf stage (9.4%). Thermal time to silking and anthesis decreased by about 1 and 0.56°C day year−1, respectively. Our data revealed that silking and anthesis can precede the final collared leaf by 96°C day (3.3 days under optimal conditions), which indicates an overlap between vegetative and reproductive phases. We concluded that maize breeding has indirectly altered the rate of vegetative development of maize hybrids without affecting the final leaf number. Present results expand our knowledge base on the genotypic variability in maize development traits, which can improve empirical and process‐based models used for crop stage and yield prediction.

Genomic selection and enablers for agronomic traits in maize (Zea mays): A review

AbstractMaize is a commodity crop providing millions of people with food, feed, industrial raw material and economic opportunities. However, maize yields in Africa are relatively stagnant and low, at a mean of 1.7 t ha−1 compared with the global average of 6 t ha−1. The yield gap can be narrowed with accelerated and precision breeding strategies that are required to develop and deploy high‐yielding and climate‐resilient maize varieties. Genomic and phenotypic selections are complementary methods that offer opportunities for the speedy choice of contrasting parents and derived progenies for hybrid breeding and commercialization. Genomic selection (GS) will shorten the crop breeding cycle by identifying and tracking desirable genotypes and aid the timeous commercialization of market‐preferred varieties. The technology, however, has not yet been fully embraced by most public and private breeding programmes, notably in Africa. This review aims to present the importance, current status, challenges and opportunities of GS to accelerate genetic gains for economic traits to speed up the breeding of high‐yielding maize varieties. The first section summarizes genomic selection and the contemporary phenotypic selection and phenotyping platforms as a foundation for GS and trait integration in maize. This is followed by highlights on the reported genetic gains and progress through phenotypic selection and GS for grain yield and yield components. Training population development, genetic design and statistical models used in GS in maize breeding are discussed. Lastly, the review summarizes the challenges of GS, including prediction accuracy, and integrates GS with speed breeding, doubled haploid breeding and genome editing technologies to increase breeding efficiency and accelerate cultivar release. The paper will guide breeders in selection and trait introgression using GS to develop cultivars preferred by the marketplace.

Genomic versus phenotypic selection to improve corn borer resistance and grain yield in maize.

The study of yield and resistance/tolerance to pest are related traits fundamental for maize breeding programs. Genomic selection (GS), which uses all marker information to calculate genomic breeding values, is presented as an emerging alternative to phenotypic and marker-assisted selections for improving complex traits controlled by many genes with small effects. Therefore, although phenotypic selection (PS) has been effective for increasing resistance and yield under high infestation with maize stem borers, higher genetic gains are expected to be obtained through GS based on the complex architecture of both traits. Our objective was to test whether GS is more effective than PS for improving resistance and/or tolerance to maize stem borers and grain yield. For this, we compared different selection programs based on phenotype and genotypic value for a single trait, resistance or yield, and for both traits together. We obtained that GS achieved the highest genetic gain for yield, meanwhile phenotypic selection for yield was the program that achieved the highest reduction of tunnel length, but was ineffective for increasing yield. However, phenotypic or genomic selection for increased resistance may be more effective in improving both traits together; although the gains per cycle would be small for both traits.

Advances in Molecular Techniques for Developing Drought-Tolerant Maize (Zea Mays L.)

Drought is one of the major limiting factors in maize (Zea mays L.) production, causing significant yield losses globally. Breeding for drought tolerance has been a key strategy in increasing maize yield in drought-prone areas. The use of molecular methods in maize breeding has facilitated the identification of genes and quantitative trait loci (QTL) associated with drought tolerance. This review summarizes the progress made in using molecular methods to identify and utilize genetic improvements in drought-tolerant maize. It covers various molecular methods used in identifying drought tolerance genes and QTLs, and the application of these findings in marker-assisted selection (MAS) and genomic selection (GS). The review also highlights the potential of CRISPR-Cas9 genome editing to improve drought tolerance in maize.

Inbred Selection for Increased Resistance to Kernel Contamination with Fumonisins.

In temperate world-wide regions, maize kernels are often infected with the fumonisin-producing fungus Fusarium verticillioides which poses food and feed threats to animals and humans. As maize breeding has been revealed as one of the main tools with which to reduce kernel contamination with fumonisins, a pedigree selection program for increased resistance to Fusarium ear rot (FER), a trait highly correlated with kernel fumonisin content, was initiated in 2014 with the aim of obtaining inbred lines (named EPFUM) with resistance to kernel contamination with fumonisins and adapted to our environmental conditions. The new released EPFUM inbreds, their parental inbreds, hybrids involving crosses of one or two EPFUM inbreds, as well as commercial hybrids were evaluated in the current study. The objectives were (i) to assess if inbreds released by that breeding program were significantly more resistant than their parental inbreds and (ii) to examine if hybrids derived from EPFUM inbreds could be competitive based on grain yield and resistance to FER and fumonisin contamination. Second-cycle inbreds obtained through this pedigree selection program did not significantly improve the levels of resistance to fumonisin contamination of their parental inbreds; however, most EPFUM hybrids showed significantly better resistance to FER and fumonisin contamination than commercial hybrids did. Although European flint materials seem to be the most promising reservoirs of alleles with favorable additive and/or dominance effects for resistance to kernel contamination with fumonisins, marketable new Reid × Lancaster hybrids have been detected as they combine high resistance and yields comparable to those exhibited by commercial hybrids. Moreover, the white kernel hybrid EPFUM-4 × EP116 exploits the genetic variability within the European flint germplasm and can be an alternative to dent hybrid cultivation because white flint grain can lead to higher market prices.