Maize Populations Research Articles

Metabolic marker-assisted genomic prediction improves hybrid breeding

Hybrid breeding is widely acknowledged as the most effective method for increasing crop yield, particularly in maize and rice. However, a major challenge in hybrid breeding is selecting desirable combinations from a vast pool of potential crosses. Genomic selection (GS) has emerged as a powerful tool to tackle this challenge, but its success in practical breeding depends on prediction accuracy. Several strategies have been explored to enhance the prediction accuracy for complex traits, such as incorporating functional markers and multi-omics data. Metabolome-wide association studies (MWAS) help identify metabolites closely linked to phenotype, known as metabolic markers. However, the use of preselected metabolic markers from parental lines to predict hybrid performance has not yet been explored. In this study, we developed a novel approach called metabolic marker-assisted genomic prediction (MM_GP) that incorporates significant metabolites identified from MWAS into GS models to improve the accuracy of genomic hybrid prediction. In maize and rice hybrid populations, MM_GP outperformed GP for all traits, regardless of the methods used (GBLUP or XGBoost). On average, MM_GP yielded 4.6% and 13.6% higher predictive abilities compared to GP in maize and rice, respectively. Additionally, MM_GP could match or even surpass the predictive ability of M_GP (integrated genomic-metabolomic prediction) for most traits. Notably, integrating only six metabolic markers significantly related to multiple traits resulted in a 5.0% and 3.1% higher average predictive ability than GP and M_GP in maize, respectively. With the advancement of high-throughput metabolomics technologies and prediction models, this approach holds great promise to revolutionize genomic hybrid breeding by enhancing its accuracy and efficiency.

Logistic and Structural Equation Fitting Analyses of the Effect of Slow-Release Nitrogen Fertilizer Application Rates on the Nitrogen Accumulation and Yield Formation Mechanism in Maize

The purpose of this study is to clarify the differential effects of the application rate of slow-release nitrogen fertilizer (SRFN) on the nitrogen (N) accumulation dynamics, nutrient organ N distribution and transportation, yield, and N utilization efficiency of maize harvested using grain-type machines. This has significant implications for the scientific application of SRFN, as well as for reducing its application rate and improving its efficiency, in the agro-pastoral transitional zone of northern China. In a long-term positioning experiment that began in 2018, five treatments consisting of different SRFN application rates were set up, namely, N120 (120 kg ha−1), N180 (180 kg ha−1), N240 (240 kg ha−1), N300 (300 kg ha−1), and N360 (360 kg ha−1), with no fertilization during the growth period used as control (CK) treatment. To explore the characteristics of nitrogen accumulation dynamics in maize populations and the main factors affecting maize yield formation under the different SRFN application rate treatments, this study adopted a combination of quantitative analyses and model fitting, including logistic models, principal component analysis, and structural equation modeling. The research results show that SRFN application increased the aboveground N accumulation of the maize population, and the fitting effect of the logistic models was significant. The maximum rate of N accumulation in both years showed a trend of first increasing and then decreasing with the increase in the SRFN application rate. Compared with CK, SRFN application reduced the proportion of N distribution in the nutrient organs during the R6 stage, and it increased the N transport from the nutrient organs to the grains after the VT-R1 stage. With the increase in the SRFN application rate, both the economic yield and biological yield showed a single peak curve change and were maximized in the N240 treatment. The economic yield reached 15,342.07 kg ha−1 in 2020 and 16,323.51 kg ha−1 in 2021, increasing by 36.2% and 61.7% compared with CK, respectively. The apparent N fertilizer recovery rate, N uptake efficiency, N agronomic efficiency, and N fertilizer partial productivity all gradually decreased with the increase in the SRFN application rate. In maize populations, an appropriate SRFN application rate can adjust the characteristic parameters during the aboveground N accumulation rapid growth period, increase the N accumulation amount in aboveground parts, promote the transport of N from nutrient organs to grains, and improve yield. An application of 180–240 kg ha−1 SRFN is recommended for maize cultivation in the agro-pastoral transitional zone of northern China, as it is beneficial for stabilizing and increasing maize yield, as well as reducing the rate and improving the efficiency of N fertilizer.

Morpho-Phenological, Chemical, and Genetic Characterization of Italian Maize Landraces from the Lazio Region.

In the framework of a Collaboration Agreement between CREA and ARSIAL, a morpho-phenological, chemical, and genetic characterization of maize populations native to the Lazio region was carried out. During 2022 and 2023, a set of 50 accessions, belonging both to ARSIAL and CREA maize collections, were multiplied in Bergamo. Morpho-phenological descriptors were recorded in the field: plant height, ear height, and male and female flowering time. The grain chemical composition in terms of protein, lipid, starch, ash and fiber was evaluated by near-infrared spectroscopy (NIRS). A double-digest restriction-site-associated DNA sequencing (ddRADseq) strategy was used to genotype the landraces. The two collections were not significantly different in terms of grain chemical composition. On the other hand, the ARSIAL and CREA germplasm showed a different distribution in the three cluster-based population structure obtained by ddRADseq, which largely corresponded to the distribution map of their collection sites. The materials from the Lazio region maintained by ARSIAL and CREA were revealed to be different. The comparison between the two groups of landraces showed the importance of characterizing germplasm collections to promote the recovery and valorization of local biodiversity.

Transgene effects vary among maize populations with implications for improving quantitative traits

AbstractThe goal of transgenesis in plant breeding is to make step‐change improvements in traits of interest. However, improving quantitative traits, such as yield in maize (Zea mays L.), with transgenes has been difficult. Traditionally, transgene testing is done on a few isogenic lines, and results are extrapolated to entire breeding populations. Testing on limited germplasm does not provide a robust estimate of a transgene's value. Incorporating transgenes directly into breeding populations could increase genetic variance and the rate of genetic gain. Here, we used a transgene that reduces ethylene as a case study and investigated event, transgene, family, and environment effects and their interactions. We also determined whether introduction of the transgene into a breeding population would result in transgenic lines being preferentially selected over nontransgenic lines for yield. We found significant variation in transgene effects across clustered environments and families for multiple traits including yield. In environmental Cluster 2, the transgenic lines yielded 0.4 Mg ha−1 more than nontransgenic lines in family KC22; yet, in family QY43, transgenic lines yielded 0.3 Mg ha−1 less. Similarly, within Cluster 4, the QY43 family had preferential selection of transgenic over nontransgenic lines, whereas in families YE41 and AY91, nontransgenic lines were selected more frequently. These results show the critical importance of evaluating transgenes across broad germplasm diversity to assess their general value to a program. Integrating transgenes, or using gene editing, directly in a breeding program can expand genetic variation for quantitative traits and potentially accelerate genetic gain.

Enhancing Across-Population Genomic Prediction for Maize Hybrids.

In crop breeding, genomic selection (GS) serves as a powerful tool for predicting unknown phenotypes by using genome-wide markers, aimed at enhancing genetic gain for quantitative traits. However, in practical applications of GS, predictions are not always made within populations or for individuals that are genetically similar to the training population. Therefore, exploring possibilities and effective strategies for across-population prediction becomes an attractive avenue for applying GS technology in breeding practices. In this study, we used an existing maize population of 5820 hybrids as the training population to predict another population of 523 maize hybrids using the GBLUP and BayesB models. We evaluated the impact of optimizing the training population based on the genetic relationship between the training and breeding populations on the accuracy of across-population predictions. The results showed that the prediction accuracy improved to some extent with varying training population sizes. However, the optimal size of the training population differed for various traits. Additionally, we proposed a population structure-based across-population genomic prediction (PSAPGP) strategy, which integrates population structure as a fixed effect in the GS models. Principal component analysis, clustering, and Q-matrix analysis were used to assess the population structure. Notably, when the Q-matrix was used, the across-population prediction exhibited the best performance, with improvements ranging from 8 to 11% for ear weight, ear grain weight and plant height. This is a promising strategy for reducing phenotyping costs and enhancing maize hybrid breeding efficiency.

ZmKTF1 promotes salt tolerance by mediating RNA-directed DNA methylation in maize.

The epigenetic process of RNA-directed DNA methylation (RdDM) regulates the expression of genes and transposons. However, little is known about the involvement of RdDM in the response of maize (Zea mays) to salt stress. Here, we isolated a salt-sensitive maize mutant and cloned the underlying gene, which encodes KOW DOMAIN-CONTAINING TRANSCRIPTION FACTOR1 (KTF1), an essential component of the RdDM pathway. Evolutionary analysis identified two homologs of KTF1 (ZmKTF1A and ZmKTF1B) with highly similar expression patterns. Whole-genome bisulfite sequencing revealed that mutations in ZmKTF1 substantially decrease genome-wide CHH (H = A, C, or T) methylation levels. Moreover, our findings suggest that ZmKTF1-mediated DNA methylation regulates the expression of multiple key genes involved in oxidoreductase activity upon exposure to salt, concomitant with increased levels of reactive oxygen species. In addition, insertion-deletion mutations (InDels) in the promoter of ZmKTF1 affect its expression, thereby altering Na+ concentrations in seedlings in a natural maize population. Therefore, ZmKTF1 might represent an untapped epigenetic resource for improving salt tolerance in maize. Overall, our work demonstrates the critical role of ZmKTF1 involved in the RdDM pathway in maize salt tolerance.

Comparative genomics of Fusarium species causing Fusarium ear rot of maize.

Fusarium ear rot (FER), caused by the fungal pathogen Fusarium verticillioides, stands as one of the most economically burdensome and pervasive diseases affecting maize worldwide. Its impact on food security is particularly pronounced due to the production of fumonisins, toxic secondary metabolites that pose serious health risks, especially for livestock. FER disease severity is complex and polygenic, with few resistance (R) genes being identified for use in breeding resistant varieties. While FER is the subject of several breeding programs, only a few studies have investigated entire populations of F. verticillioides with corresponding virulence data to better understand and characterize the pathogenomics. Here, we sequenced and compared the genomes of 50 Fusarium isolates (43 F. verticillioides and 7 other Fusarium spp.) that were used to inoculate a diverse maize population. Our objectives were to elucidate the genome size and composition of F. verticillioides, explore the variable relationship between fumonisin production and visual disease severity, and shed light on the phylogenetic relationships among the isolates. Additionally, we conducted a comparative analysis of the nucleotide variants (SNPs) and the isolates' effectoromes to uncover potential genetic determinants of pathogenicity. Our findings revealed several promising leads, notably the association of certain gene groups, such as pectate lyase, with disease severity. These genes should be investigated further as putative alleles for breeding resistant maize varieties. We suggest that, beyond validation of the alleles identified in this study, researchers validate each phenotypic dataset on an individual basis, particularly if considering fumonisin concentrations and when using diverse populations. Our study underscores the importance of genomic analysis in tackling FER and offers insights that could inform the development of resilient maize cultivars. By leveraging advances in genomics and incorporating pathogen populations into breeding programs, resistance to FER can be advanced.

Study of co-localization of QTL for drought tolerance of morphological traits in teosinte introgressed maize population

Study of co-localization of QTL for drought tolerance of morphological traits in teosinte introgressed maize population

Genome-wide association analysis of grain yield and Striga hermonthica and S. asiatica resistance in tropical and sub-tropical maize populations

BackgroundGenetic improvement for Striga hermonthica (Sh) and S. asiatica (Sa) resistance is the most economical and effective control method to enhance the productivity of maize and other major cereal crops. Hence, identification of quantitative trait loci (QTL) associated with Striga resistance and economic traits will guide the pace and precision of resistance breeding in maize. The objective of this study was to undertake a genome-wide association analysis of grain yield and Sh and Sa resistance among tropical and sub-tropical maize populations to identify putative genetic markers and genes for resistance breeding. 126 maize genotypes were evaluated under controlled environment conditions using artificial infestation of Sh and Sa. The test genotypes were profiled for grain yield (GY), Striga emergence counts at 8 (SEC8) and 10 (SEC10) weeks after planting, and Striga damage rate scores at 8 (SDR8) and 10 (SDR10) weeks after planting. Population structure analysis and genome-wide association mapping were undertaken based on 16,000 single nucleotide polymorphism (SNP) markers.ResultsA linkage disequilibrium (LD) analysis in 798,675 marker pairs revealed that 21.52% of pairs were in significant linkage (P < 0.001). Across the chromosomes, the LD between SNPs decayed below a critical level (r2 = 0.1) at a map distance of 0.19 Mbp. The genome-wide association study identified 50 significant loci associated with Sh resistance and 22 significant loci linked to Sa resistance, corresponding to 39 and 19 candidate genes, respectively.ConclusionThe study found non-significant QTL associated with dual resistance to the two examined Striga species Some of the detected genes reportedly conditioned insect and pathogen resistance, plant cell development, variable senescence, and pollen fertility. The markers detected in the present study for Sa resistance were reported for the first time. The gene Zm00001eb219710 was pleiotropic, and conditioned GY and SEC10, while Zm00001eb165170 affected SDR8 and SDR10, and Zm00001eb112030 conditioned SDR8 and SDR10 associated with Sh resistance. The candidate genes may facilitate simultaneous selection for Sh and Sa resistance and grain yield in maize after further validation and introgression in breeding pipelines. Overall, we recommend breeding maize specifically for resistance to each Striga species using germplasm adapted to the endemic region of each parasite.

Caracterización morfoagronómica de poblaciones de maíz criollo (Zea mays L.), provincia de Manabí, Ecuador

Ecuador is a country with a wide genetic diversity of maize and there are populations of native maize conserved by farmers that have not yet been characterized. These genetic resources could be conserved and used in plant breeding programs. The objective of this research was to characterize the morpho-agronomic diversity of 38 populations of native maize from the province of Manabí, Ecuador, using 19 quantitative and 11 qualitative morpho-agronomic descriptors. During the dry season of 2022 (July - December) at the Portoviejo Experimental Station of the National Institute of Agricultural Research (INIAP), plots of 8 m2 were established for each population of native maize, with 0.3 m between plants and 0.8 m between furrows and each furrow was 5 m long. Cluster analysis showed the formation of four groups, where the populations of hard kernels with large ears and soft kernels with short ears were separated into different groups. The quantitative variables ear height, panicle length, percentage of lodging, number of kernels per row and biomass of the inflorescence rachis recorded "D" indices of 0.75, showing themselves as discriminant variables in the formation of the groups, while the most discriminating qualitative variables were kernel type (χ2 = 49.09***, P= 0.742, V= 0.64), kernel color (χ2= 51.955***, P= 0.75, V=0.64), row arrangement (χ2= 18.11*, P=0.56, V=0.39), and kernel surface shape (χ2 = 20.52*, P=0.58, V=0.41). The native maize races identified were Candela, Cubano, Tuxpeño, Tusilla, and Uchima, observing significant genetic diversity in the populations studied. It was concluded that the characterized native maize populations were a valuable genetic resource for the conservation and use of this cereal. Keywords: genotypes, landraces, genetic variability, conservation of genetic resources.

Trait association and prediction through integrative k-meranalysis.

Genome-wide association study (GWAS) with single nucleotide polymorphisms (SNPs) has been widely used to explore genetic controls of phenotypic traits. Alternatively, GWAS can use counts of substrings of length k from longer sequencing reads, k-mers, as genotyping data. Using maize cob and kernel color traits, we demonstrated that k-mer GWAS can effectively identify associated k-mers. Co-expression analysis of kernel color k-mers and genes directly found k-mers from known causal genes. Analyzing complex traits of kernel oil and leaf angle resulted in k-mers from both known and candidate genes. A gene encoding a MADS transcription factor was functionally validated by showing that ectopic expression of the gene led to less upright leaves. Evolution analysis revealed most k-mers positively correlated with kernel oil were strongly selected against in maize populations, while most k-mers for upright leaf angle were positively selected. In addition, genomic prediction of kernel oil, leaf angle, and flowering time using k-mer data resulted in a similarly high prediction accuracy to the standard SNP-based method. Collectively, we showed k-mer GWAS is a powerful approach for identifying trait-associated genetic elements. Further, our results demonstrated the bridging role of k-mers for data integration and functional gene discovery.

Identification of Transposon Insertion Sites in MaizeMu-Tagged Mutants Using Mu-Seq

Mutator(Mu) transposons facilitate untargeted insertional mutagenesis in maize by moving within the genome and disrupting genes. Such an approach has been used to generate collections such as theBonnMuresource, aMu-tagged maize population for functional genomics studies. Mutant-Seq (Mu-Seq) is a sequencing-based method for the high-throughput identification and mapping ofMuinsertion sites. The approach involves the construction of multiplexed sequencing libraries (known as Mu-Seq libraries) fromMu-tagged populations, followed by high-throughput sequencing and data processing using the Mu-Seq Workflow Utility (MuWU) tool, to determine the location ofMuinsertions. Here, we provide a detailed protocol for Mu-Seq, from the generation of the maizeMu-tagged mutant population to data analysis. Researchers can use this approach to develop mutant collections customized to specific genetic backgrounds of interest, which can aid in characterizing genotype-specific mutations and identifying candidate genes linked to visible mutant phenotypes.

Influence of Mating Systems on Trait Associations in Segregating Populations of Maize (Zea mays L.) Double Cross

In the present challenging scenario of climate change, it is essential to breed maize cultivars that withstand stress especially abiotic stresses in a broader sense. Diversification of existing germplasm is invariable to harness the actual potential of maize hybrids which are bred for specific agroecosystems. Double crosses interact less with environment compared to single crosses and their broad parentage enables better performance under varied situations of cultivation. In the present study, impact of mating systems ie., self pollination, sib mating and open pollination was studied in a high yielding double cross of maize so as to identify robust and diverse recombinants. The double cross, (BML-32 x BML-6) x (BML-10 x BML-7) was imposed with the three types of mating systems for three consecutive seasons and the resultant S3 (F4) populations were evaluated for trait interrelationssips. It was observed that sib mating established stronger and highest number of positive correlations with seven and twelve additional positive correlations than self and open pollinations respectively among the yield and its attributing traits in its progenies. Therefore deploying sib mating cycles during line development may result in more effective selection processes. Results of path analysis, however, did not significantly vary with the mating type though sib mating showed lowest residual effect.

Genetic diversity analysis of tropical and sub-tropical maize germplasm for Striga resistance and agronomic traits with SNP markers.

Striga hermonthica (Sh) and S. asiatica (Sa) are major parasitic weeds limiting cereal crop production and productivity in sub-Saharan Africa (SSA). Under severe infestation, Striga causes yield losses of up to 100%. Breeding for Striga-resistant maize varieties is the most effective and economical approach to controlling the parasite. Well-characterized and genetically differentiated maize germplasm is vital to developing inbred lines, hybrids, and synthetic varieties with Striga resistance and desirable product profiles. The objective of this study was to determine the genetic diversity of 130 tropical and sub-tropical maize inbred lines, hybrids, and open-pollinated varieties germplasm using phenotypic traits and single nucleotide polymorphism (SNP) markers to select Striga-resistant and complementary genotypes for breeding. The test genotypes were phenotyped with Sh and Sa infestations using a 13x10 alpha lattice design with two replications. Agro-morphological traits and Striga-resistance damage parameters were recorded under a controlled environment. Further, high-density Diversity Array Technology Sequencing-derived SNP markers were used to profile the test genotypes. Significant phenotypic differences (P<0.001) were detected among the assessed genotypes for the assessed traits. The SNP markers revealed mean gene diversity and polymorphic information content of 0.34 and 0.44, respectively, supporting the phenotypic variation of the test genotypes. Higher significant variation was recorded within populations (85%) than between populations using the analysis of molecular variance. The Structure analysis allocated the test genotypes into eight major clusters (K = 8) in concordance with the principal coordinate analysis (PCoA). The following genetically distant inbred lines were selected, displaying good agronomic performance and Sa and Sh resistance: CML540, TZISTR25, TZISTR1248, CLHP0303, TZISTR1174, TZSTRI113, TZDEEI50, TZSTRI115, CML539, TZISTR1015, CZL99017, CML451, CML566, CLHP0343 and CML440. Genetically diverse and complementary lines were selected among the tropical and sub-tropical maize populations that will facilitate the breeding of maize varieties with Striga resistance and market-preferred traits.

Maize Anthesis-Silking Interval Estimation via Image Detection under Field Rail-Based Phenotyping Platform

The Anthesis-Silking Interval (ASI) is a crucial indicator of the synchrony of reproductive development in maize, reflecting its sensitivity to adverse environmental conditions such as heat stress and drought. This paper presents an automated method for detecting the maize ASI index using a field high-throughput phenotyping platform. Initially, high temporal-resolution visible-light image sequences of maize plants from the tasseling to silking stage are collected using a field rail-based phenotyping platform. Then, the training results of different sizes of YOLOv8 models on this dataset are compared to select the most suitable base model for the task of detecting maize tassels and ear silks. The chosen model is enhanced by incorporating the SENetv2 and the dual-layer routing attention mechanism BiFormer, named SEBi-YOLOv8. The SEBi-YOLOv8 model, with these combined modules, shows improvements of 2.3% and 8.2% in mAP over the original model, reaching 0.989 and 0.886, respectively. Finally, SEBi-YOLOv8 is used for the dynamic detection of maize tassels and ear silks in maize populations. The experimental results demonstrate the method’s high detection accuracy, with a correlation coefficient (R2) of 0.987 and an RMSE of 0.316. Based on these detection results, the ASI indices of different inbred lines are calculated and compared.

Potential of Tropically-Adapted Exotic Acid Tolerance White Maize Donor Lines in Sub-tropical Breeding Programmes for Low pH Adaptation

Low pH in soils is attributed as the main contributor to the low yields characteristic in maize production regions of Angola. Here, eight white-kernel acid soil tolerant donor lines (ASTDLs) sourced from CIMMYT-Colombia (testers) were crossed with eight white elite lines adapted to the mid-altitude climatic conditions from CIMMYT-Zimbabwe, in order to identify donor lines, which can be potential sources of acid tolerance genes in breeding programmes in Angola. The two groups of parents were crossed using a line by tester (L&amp;times;T) mating design, yielding 47 crosses with sufficient seed, which were evaluated alongside eight acid tolerant commercial hybrids, during the 2014-16 cropping seasons at nine sites, representing acid and non-acid soils in Angola and Zimbabwe. Effects of general combining ability (GCA) due to lines and testers, as well as specific combining ability (SCA) on grain yield were significant (P &amp;lt; 0.05) under acid soils. From the CIMMYT-Zimbabwe breeding programme, inbred lines identified as ZW1, ZW4 and ZW5 together with the CIMMYT-Colombia ASTDLs (i.e., CW4 and CW8) seemed to be ideal parents for crosses that can do well under both the acid and non-acid soils. The best specific cross for acid soils was identified as ZW1 &amp;times; CW8 (CH142512), whereas for non-acid soils, ZW3 &amp;times; CW4 (CH142500) was identified. Interestingly, the cross ZW1 &amp;times; CW8 was also observed as stable under both acid and non-acid soil conditions. Overall, data showed potential of exotic acid tolerance donor lines for enhancing low-pH adaptation in sub-tropical maize populations.

Effects of Planting Density and Nitrogen Management on Light and Nitrogen Resource Utilization Efficiency and Yield of Summer Maize in the Sichuan Hilly Region

The low efficiency of light and nitrogen resources, poor yield and profit, and environmental pollution of maize production are main problems in many areas of China. We hypothesized that optimizing nitrogen fertilizer density management strategies could alleviate the above issues. To address this, a 3-year on-site experiment with three planting densities and four nitrogen rates was conducted in the Sichuan Hilly Region. The results indicated that increasing the planting density could increase the extinction coefficient and solar radiation interception of maize populations as well as enhance the utilization efficiency of light and nitrogen resources and yield. For every 100 kg ha−1 increase in nitrogen fertilizer, RUE increased by 0.16%, NUE decreased by 25.0%, and soil apparent nitrogen loss quantity increased by 67.8 kg ha−1. There was a certain interaction between planting density and nitrogen rate. The appropriate planting density and nitrogen rate combination was 67,500 plants ha−1 with 180 kg N ha−1 under the experimental condition. Excessive close planting in weak-light areas and excessive nitrogen reduction after densification are not advisable. This study indicated that nitrogen–density strategies should be matched with the local natural resources such as sunlight. The results provide a theoretical for high-yield and high-quality maize production in these areas.

Damage and Entomophagy in Natural Infestations of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Maize Landraces in Oaxaca, Mexico1

Abstract The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), seriously damages maize (Zea mays L.) crops in tropical, subtropical, and temperate zones of Mexico and around the world. This study was conducted to evaluate the damage caused by S. frugiperda to six native maize populations and the natural parasites of S. frugiperda in three localities from Oaxaca, Mexico. Two native maize populations each of the Zapalote Chico, Bolita, and Conico-Chalqueño races were used. Plantings were done at Coatecas Altas, Santa Lucia Miahuatlan, and Villa de Zaachila under a randomized complete block design with four replications. The agroecological conditions of cultivation influenced the damage caused by S. frugiperda and influenced its natural parasitism. The ordered weighted mean damage in the localities was Villa de Zaachila (1.40–4.92) &amp;gt; Coatecas Altas (1.33–4.06) &amp;gt; Santa Lucia Miahuatlan (0.53–1.00). The order of parasitism rates in the localities was Villa de Zaachila (56.16%) ≈ Santa Lucia Miahuatlan (37.59%) &amp;gt; Coatecas Altas (14.27%). Zapalote Chico populations were less damaged by S. frugiperda larvae and flowered earlier than did the Conico-Chalqueño and Bolita populations. Thirteen parasitoid species and nematodes were recorded attacking S. frugiperda. Chelonus insularis Cresson was the most abundant parasitoid species across the locations. Members of 17 families of predators and 12 families of parasitoids also were identified as potential natural enemies of S. frugiperda. The population dynamics of this armyworm were determined by the environmental conditions of the location, maize population, transition from the vegetative to the reproductive stage, and presence of natural enemies, whereas natural parasitism was influenced only by location.

Genomic loci associated with grain yield under well-watered and water-stressed conditions in multiple bi-parental maize populations

Smallholder maize farming systems in sub-Saharan Africa (SSA) are vulnerable to drought-induced yield losses, which significantly impact food security and livelihoods within these communities. Mapping and characterizing genomic regions associated with water stress tolerance in tropical maize is essential for future breeding initiatives targeting this region. In this study, three biparental F3 populations composed of 753 families were evaluated in Kenya and Zimbabwe and genotyped with high-density single nucleotide polymorphism (SNP) markers. Quantitative trait loci maping was performed on these genotypes to dissect the genetic architecture for grain yield (GY), plant height (PH), ear height (EH) and anthesis-silking interval (ASI) under well-watered (WW) and water-stressed (WS) conditions. Across the studied maize populations, mean GY exhibited a range of 4.55–8.55 t/ha under WW and 1.29–5.59 t/ha under WS, reflecting a 31–59% reduction range under WS conditions. Genotypic and genotype-by-environment (G × E) variances were significant for all traits except ASI. Overall broad sense heritabilities for GY were low to high (0.25–0.60). For GY, these genetic parameters were decreased under WS conditions. Linkage mapping revealed a significant difference in the number of QTLs detected, with 93 identified under WW conditions and 41 under WS conditions. These QTLs were distributed across all maize chromosomes. For GY, eight and two major effect QTLs (&amp;gt;10% phenotypic variation explained) were detected under WW and WS conditions, respectively. Under WS conditions, Joint Linkage Association Mapping (JLAM) identified several QTLs with minor effects for GY and revealed genomic region overlaps in the studied populations. Across the studied water regimes, five-fold cross-validation showed moderate to high prediction accuracies (−0.15–0.90) for GY and other agronomic traits. Our findings demonstrate the polygenic nature of WS tolerance and highlights the immense potential of using genomic selection in improving genetic gain in maize breeding.

Cardinal temperatures of populations developed from native maize (Zea mays L.) from central and southern, Tamaulipas, Mexico

Objective: To estimate the cardinal temperatures of native maize populations from Tamaulipas. Design/Methodology/Approach: Ten genotypes developed from native germplasms were established in Güémez, Tamaulipas, on 12 planting dates (2019 and 2020). The cardinal temperatures (Tb, To, and Tu) of each of the cultivars were estimated through the decomposition of a quadratic model, using the days from sowing to tasseling and the average temperature of each sowing date from that period. Results: From sowing to tasseling, the evaluated cultivars recorded 15.7-18.1 °C base temperatures (Tb), 28.3-30.1 °C optimum temperatures (To), and 32.3-34.4 °C threshold temperatures (Tu). The Tb and To values represent the high thermal requirement of the germplasm, while Tu stands for its resistance to high temperatures. The L3, L4, L5, and VHA cultivars stood out for their broader adaptation range (16.2 to 34.4 °C), while the L3, L4, and L6 cultivars have a higher resistance to high temperatures (average Tu: 34.5 °C). Study Limitations/Implications: The cardinal temperatures determined in this study depended on the evaluated genotypes and the environment in which they developed. Findings/Conclusions: The maize germplasm evaluated in this study was resistant to high temperatures. As a result of its adaptation to the conditions of central and southern Tamaulipas, this germplasm is a source of variation for the characteristics that provide resistance to the stress caused by high temperatures.