Maize Improvement Research Articles

Dynamic physiological and transcriptomic changes reveal memory effects of salt stress in maize

BackgroundPre-exposing plants to abiotic stresses can induce stress memory, which is crucial for adapting to subsequent stress exposure. Although numerous genes involved in salt stress response have been identified, the understanding of memory responses to salt stress remains limited.ResultsIn this study, we conducted physiological and transcriptional assays on maize plants subjected to recurrent salt stress to characterize salt stress memory. During the second exposure to salt stress, the plants exhibited enhanced salt resistance, as evidenced by increased proline content and higher POD and SOD activity, along with decreased MDA content, indicative of physiological memory behavior. Transcriptional analysis revealed fewer differentially expressed genes and variations in response processes during the second exposure compared to the first, indicative of transcriptional memory behavior. A total of 2,213 salt stress memory genes (SMGs) were identified and categorized into four response patterns. The most prominent group of SMGs consisted of genes with elevated expression during the first exposure to salt stress but reduced expression after recurrent exposure to salt stress, or vice versa ([+ / −] or [− / +]), indicating that a revised response is a crucial process in plant stress memory. Furthermore, nine transcription factors (TFs) (WRKY40, WRKY46, WRKY53, WRKY18, WRKY33, WRKY70, MYB15, KNAT7, and WRKY54) were identified as crucial factors related to salt stress memory. These TFs regulate over 53% of SMGs, underscoring their potential significance in salt stress memory.ConclusionsOur study demonstrates that maize can develop salt stress memory, and the genes identified here will aid in the genetic improvement of maize and other crops.

DEFECTIVE KERNEL 56 functions in mitochondrial RNA editing and maize seed development.

Proper seed development is essential for achieving grain production, successful seed germination, and seedling establishment in maize (Zea mays). In the past few decades, pentatricopeptide repeat (PPR) proteins have been proven to play an essential role in regulating the development of maize kernels through posttranscriptional RNA modification of mitochondrial genes. However, the underlying mechanisms remain largely unknown. Here, we characterized a mutant of DEFECTIVE KERNEL 56 (DEK56) with defective kernels that exhibited arrested development of both the embryo and endosperm. Accordingly, we isolated DEK56 through a map-based cloning strategy and found that it encoded an E subgroup PPR protein located in the mitochondria. Dysfunction of DEK56 resulted in altered cytidine (C)-to-uridine (U) editing efficiency at 48 editing sites across 21 mitochondrial transcripts. Notably, the editing efficiency of the maturase-related (matR)-1124 site was substantially reduced or abolished in the dek56 mutant. Furthermore, we found that the splicing efficiency of NADH dehydrogenase subunit 4 (nad4) Introns 1 and 3 was substantially reduced in dek56 kernels, which might be a consequence of the defective MatR function. Through a protein-protein interaction test, we hypothesized that DEK56 carries out its function by recruiting the PPR-DYW protein PPR motif, coiled-coil, and DYW domain-containing protein 1 (PCW1). This interaction is facilitated by Multiple Organellar RNA Editing Factors (ZmMORFs) and Glutamine-Rich Protein 23 (ZmGRP23). Based on these findings, we developed a working model of PPR-mediated mitochondrial processing that plays an essential role in the development of maize kernels. The present study will further broaden our understanding of PPR-mediated seed development and provide a theoretical basis for maize improvement.

Genome wide association analysis reveals multiple QTLs controlling root development in maize

Maize root system plays a crucial role in the development of the aboveground plant and determines the yield via the uptake of water and nutrients in the field. However, the genetic architecture of the maize root system is largely unknown mainly due to the complexity of maize root system and the interaction between genotype and environment. Using a high-throughput semi-automatic hydroponic platform with stable conditions, we comprehensively characterized the root system in a core population of 518 diverse inbred lines of maize. Population structure analysis revealed that the panel has a stratification and linkage disequilibrium decay distance was less than 50 Kb. Based on the genotyping with the high density of 600 K SNPs, we conducted a genome wide association analysis (GWAS) and identified nine SNPs and seven candidate genes significantly associated with 24 traits. A candidate gene GRMZM2G400533 located at the upstream 5 Kb region from the leading SNP (AX-91771718) was significantly associated with primary root length and preferentially expressed in primary root and crown root. The expression of GRMZM2G400533 increased as the primary root developed but negatively correlated with primary root elongation. We also identified three functional variants and eight allelic haplotypes based on candidate gene analysis of GRMZM2G400533. The present study will broaden our understanding of maize root development and provide a theoretical basis for maize improvement through optimizing root system.

Uncovering microsatellite markers associated with agronomic traits of South Sudan landrace maize.

Maize has great importance in South Sudan as the most cultivated cereal after sorghum; however, numerous challenges are encountered in its production. To raise maize production, it is critical to exploit the wealth of its genetic variation for grain yield enhancement. This study aimed to conduct association analysis to identify specific simple sequence repeat (SSR) markers associated with quantitative agronomic traits. Genetic variation and population structure were investigated among 31 maize accessions by association analysis using 50 SSR markers and seven quantitative agronomic traits. The genotypes exhibited abundant genetic variation, and 418 alleles were detected with an average of 8.4 alleles per locus. The average genetic diversity, major allele frequency, and polymorphic information content were 0.754, 0.373, and 0.725, respectively. The population structure based on 50 SSR markers divided the maize accessions into two main groups and an admixed group without considering their descent. Association analysis was performed using a general linear model (Q GLM) and a mixed linear model (Q + K MLM). Q GLM detected 44 trait-marker associations involving 23 SSR markers. Q + K MLM detected four marker-trait associations involving three SSR markers (umc2286, umc1303, umc1429) associated with days to tasseling, days to silking, leaf length, and leaf width. The detected significant SSR markers related to agronomic traits could be useful for future genetic studies. Additionally, markers affecting several agronomic traits and overlapped SSR markers require further testing on a wide range of genotypes prior to their consideration as candidate markers for marker assisted selection for South Sudan maize improvement.

Heterotic grouping of provitamin A-enriched maize inbred lines for increased provitamin A content in hybrids

BackgroundThe establishment of heterotic groups of inbred lines is crucial for hybrid maize breeding programs. Currently, there is no information on the heterotic patterns of the Provitamin A (PVA) inbred lines developed in the maize improvement program of the International Institute of Tropical Agriculture (IITA) to form productive PVA enriched hybrids for areas affected by vitamin A deficiency. This study assessed the feasibility of classifying PVA-enriched inbred lines into heterotic groups based on PVA content without compromising grain yield in hybrids. Sixty PVA inbred lines were crossed to two testers representing two existing heterotic groups. The resulting 120 testcrosses hybrids were evaluated for two years at four locations in Nigeria.ResultsThe two testers effectively classified the inbred lines into two heterotic groups. The PVA-based general combining ability and specific combining ability (HSGCA) method assigned 31 and 27 PVA enriched maize inbred lines into HGB and HGA, respectively, leaving two inbred lines not assigned to any group. The yield-based HSGCA method classified 32 inbred lines into HGB and 28 inbred lines into HGA. Both PVA and yield-based heterotic grouping methods assigned more than 40% of the inbred lines into the same heterotic groups. Even though both PVA and yield-based heterotic grouping of the inbred lines differed from the clusters defined by the DArTag SNP markers, more than 40% of the inbred lines assigned to HGA were present in Cluster-1 and 60% of the inbred lines assigned to HGB were present in Cluster-3. Interestingly, the inbred lines assigned to the same heterotic groups based on PVA content and grain yield were distributed across the three Ward’s clusters. The PVA-based HSGCA was identified as the most effective heterotic grouping method for breeding programs working on PVA biofortification.ConclusionsSelecting PVA enriched maize inbred lines with diverse genetic backgrounds from the three marker-based clusters may facilitate the development of productive hybrids with high PVA content and for generating source populations to develop more vigorous maize inbred lines with much higher concentrations of PVA.

Unveiling the potential of acidified cow dung in combination with plant growth promoting endophytes on growth, physiology, and yield improvement of maize in salt-affected soil

Unveiling the potential of acidified cow dung in combination with plant growth promoting endophytes on growth, physiology, and yield improvement of maize in salt-affected soil

Genetic Variability, Heritability and Genetic Advance for Yield and its Related Traits in Maize (Zea mays L.) Inbred Lines as Influenced by Drought and Heat Stress Conditions in Sudan Savannah of Nigeria

The experiments were conducted during the dry seasons of 2021 and 2022 at research farm of Kano University of Science and Technology Wudil and Farmers field at Dambatta Local Government Area, to evaluate the genetic analysis of maize inbred lines under combined drought and heat stress conditions. The parental materials comprise of eight inbred lines that were crossed in a partial diallel pattern. The 64 genotypes were arranged in a 99 lattice design with three replications at each location. Each plot consists of two rows 4 m long, with inter and intra row spacing of 75 cm x 25 cm respectively. Sowing was done manually in February 2022; two seeds per hill were sown 0.25 x 0.75m, with a seed bed of 2.5 x 2.5m (6.25m2) and later thinned to one plant per hill. Irrigation water was applied to field capacity once every week to all the conditions during the first 5 weeks (35 days) after sowing. The well- watered and stress conditions were separated from each other by 2.5m alley to prevent spill-over at the water stress sites during the period of imposed water and drought stress and at the beginning and end of each replication; non experimental lines were raised to minimize the edge border effects. The results of analysis of variance revealed that the genotypes exhibited highly significant differences for plant aspect, ear aspect, grain weight and grain yield across the two locations indicated the existence of sufficient genetic variability among the selected materials and scope for improvement in maize. High GCV and PCV was recorded in anthesis silking interval and grain yield showing high variability of the trait, while moderate GCV and PCV was observed for ear height, ears per plant, plant aspect and ear aspect indicating moderate variability among the genotypic trait. Other trait recorded low GCV and PCV. The result shows high heritability accompanied by high genetic advance as percent of mean (GAM) for as to 50% flowering and days to 50% silking which indicated the preponderance of additive gene action in controlling the traits. Hence direct selection of such characters would be effective in improving for the inheritance of the affected traits. Therefore trait could be improved through breeding method such as simple selection, single seed decent. Low heritability and GAM observed for other traits were influenced by non-additive gene effects for the inheritance of the trait and could be dependable for their improvement in maize.

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.

Genetic Variances, Heritability and Traits Association of Early Maturing Maize Hybrids under Induced Drought at Seedling and Flowering Stages

Aims: Information on traits association and inheritance are crucial to designing appropriate breeding strategies for improving maize production and productivity in drought-prone ecologies. The objectives of this study were to investigate inter-trait relationships among maize hybrids and estimate genetic variances and heritability of drought tolerance parameters under seedling and flowering drought conditions.
 Methodology: Sixty-six single cross hybrids generated using diallel mating design plus nine hybrid checks were evaluated using a 5 x 15 alpha lattice and randomized complete block designs in three replicates on the field and in the screenhouse respectively, during 2015 cropping season. Data were collected on grain yield, ears per plant, anthesis-silking interval, seedling aspect, chlorophyll content and leaf area and these data were subjected to analysis of variance as well as correlation and path coefficient analyses.
 Results: Significant mean squares (P = .05) were observed for all measured traits except leaf area and shoot fresh weight. Narrow-sense heritability estimate for grain yield was moderate (33.4%) on the field and low (0 – 25%) for all the seedling traits. The low narrow-sense heritability estimates observed for most seedling traits implied that the scope for improvement of these traits in the genotypes is limited. Seedling traits under drought stress were not directly correlated with grain yield on the field except number of dead leaves relative to the total number of leaves. Results of the path analysis revealed that number of leaves, number of dead leaves and chlorophyll content under the screenhouse conditions had significant direct effects on grain yield on the field.
 Conclusion: Number of leaves, and chlorophyll content under drought at seedling stage could therefore be used as indicator traits for grain yield improvement in maize exposed to drought stress at flowering stage.

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.

Morpho-physiological traits and SSR markers-based analysis of relationships and genetic diversity among fodder maize landraces in India.

Maize is an excellent fodder crop due to its high biomass, better palatability, succulency, and nutrition. Studies on morpho-physiological and biochemical characterization of fodder maize are limited. The present study aimed to explore the genetic variation in fodder maize landraces for various morpho-physiological traits and estimation of genetic relationship and population structure. The study on 47 fodder maize landraces revealed significant variation for all morpho-physiological traits except leaf-stem ratio. Plant height, stem girth, leaf-width and number of leaves showed positive correlation with green fodder yield. Morpho-physiological traits-based clustering grouped the landraces into three major clusters, whereas neighbour joining cluster and population structure analysis using 40 SSR markers revealed four and five major groups, respectively. Most landraces of Northern Himalaya-Kashmir and Ludhiana fall into a single group, whereas rest groups mainly had landraces from North-Eastern Himalaya. A total of 101 alleles were generated with mean polymorphic information content value of 0.36 and major allele frequency of 0.68. The pair wise genetic dissimilarity between genotypes ranged from 0.21 to 0.67. Mantel test revealed weak but significant correlation between morphological and molecular distance. Biochemical characterisation of superior landraces revealed significant variation for neutral detergent fibre, acid detergent fibre, cellulose and lignin content. Interestingly, significant, and positive correlation of SPAD with lignin content can be explored to bypass the costly affair of invitro quality assessment for digestibility parameters. The study identified superior landraces and demonstrated the use of molecular markers in genetic diversity assessment and grouping of genotypes for fodder maize improvement.

Productivity and profitability improvement of fodder maize under combined application of indigenously prepared panchagavya with organic and inorganic sources of nutrient

Irrational use of chemical fertilizers creates harmful effects on soil health and thus, led to a drop in crop productivity in the Indo-Gangetic Plains region (IGPR) of India. Organic nutrient sources such as Panchagavya and PGPR can be used to replace some proportion of chemical fertilizers to sustain productivity and soil health in the IGPR belt. This study was undertaken to determine the effect of integrated use of chemical fertilizers, organic manures and bio-fertilizers such as Panchagavya and PGPR on the productivity and economic feasibility of different maize cultivars. Results indicated that the J-1006 cultivar showed significantly higher fodder yield, nutrient use efficiencies and profitability than P-3396 and African Tall during both years. Though, nutrient content and accumulation were statistically at par with J-1006 and P-3396, but superior over African Tall. Among nutrient management, the maize fertilized with 75% RDF + PGPR +Panchagavya spray showed significantly higher fodder yield, nutrient content, accumulation, nutrient use efficiencies and net returns compared to control and 100% RDF. Overall, the growing of maize cv. J-1006 with the application of 75% RDF + PGPR + Panchagavya spray can be recommended to enhance fodder productivity, nutrient accumulation and profitability in the IGPR belt of India.

Will future maize improvement programs leverage the canopy light-interception, photosynthetic, and biomass capacities of traditional accessions?

Maize germplasm has greater latent potential to address the global food and feed crisis because of its high radiation, water and nutrient efficiencies. Photosynthetic and canopy architectural traits in maize are important in determining yield. The present study aimed to screen a subset of local maize accessions in Sri Lanka to evaluate their photosynthetic, biomass and yield related traits and to identify resource efficient germplasm. Experiments were carried out in the Ampara district of Sri Lanka. Eight maize accessions viz; SEU2, SEU6, SEU9, SEU10, SEU14, SEU15, SEU17 and SEU17 and two elite F1 cultivars (cv. Pacific-999 and cv. Bhadra) were analyzed under field conditions. Our results showed that maize genotypes produced a lower leaf area index (LAI) at the third and tenth week after field planting (WAP). However, the LAI was significantly increased in six WAP by Pacific-999, SEU2, SEU9, and SEU15. A similar trend was observed for percentage of light interception at three WAP (47%), six WAP (>64%), and decreased at 10 WAP. In addition, LAI maximum values were between 3.0 and 3.5, allowing 80% of the incident light to be intercepted by maize canopies. The estimated light extinction coefficient (k) remained lower (<0.5), suggesting that maize leaves are eractophilic canopies. Although fractional interception (f) varies, SEU2 and SEU9 had the highest values (0.57), and quantum yields of PSII (>0.73) in dark-adapted leaves. In addition, Pacific-999, SEU2, SEU9, and SEU17 had significantly higher rates of photosynthesis with minimal stomatal conductance and transpiration rates. As a result, they outperformed the control plants in terms of biomass, cob weight and grain yield. This suggests that native maize germplasm could be introduced as novel, less resource-intensive cultivars to sustain global food security.

QTL-seq and transcriptomic integrative analyses reveal two positively regulated genes that control the low-temperature germination ability of MTP–maize introgression lines

Two candidate genes (ZmbZIP113 and ZmTSAH1) controlling low-temperature germination ability were identified by QTL-seq and integrative transcriptomic analyses. The functional verification results showed that two candidate genes positively regulated the low-temperature germination ability of IB030. Low-temperature conditions cause slow maize (Zea mays L.) seed metabolism, resulting in slow seedling emergence and irregular seedling emergence, which can cause serious yield loss. Thus, improving a maize cultivar's low-temperature germination ability (LTGA) is vital for increasing yield production. Wild relatives of maize, such as Z. perennis and Tripsacum dactyloides, are strongly tolerant of cold stress and can thus be used to improve the LTGA of maize. In a previous study, the genetic bridge MTP was constructed (from maize, T. dactyloides, and Z. perennis) and used to obtain a highly LTGA maize introgression line (IB030) by backcross breeding. In this study, IB030 (Strong-LTGA) and Mo17 (Weak-LTGA) were selected as parents to construct an F2 offspring. Additionally, two major QTLs (qCS1-1 and qCS10-1) were mapped. Then, RNA-seq was performed using seeds of IB030 and the recurrent parent B73 treated at 10°C for 27 days and 25°C for 7 days, respectively, and two candidate genes (ZmbZIP113 and ZmTSAH1) controlling LTGA were located using QTL-seq and integrative transcriptomic analyses. The functional verification results showed that the two candidate genes positively regulated LTGA of IB030. Notably, homologous cloning showed that the source of variation in both candidate genes was the stable inheritance of introgressed alleles from Z. perennis. This study was thus able to analyze the LTGA mechanism of IB030 and identify resistance genes for genetic improvement in maize, and it proved that using MTP genetic bridge confers desirable traits or phenotypes of Z. perennis and tripsacum essential to maize breeding systems.

Genetic dissection of crown root traits and their relationships with aboveground agronomic traits in maize

The crown root system is the most important root component in maize at both the vegetative and reproductive stages. However, the genetic basis of maize crown root traits (CRT) is still unclear, and the relationship between CRT and aboveground agronomic traits in maize is poorly understood. In this study, an association panel including 531 elite maize inbred lines was planted to phenotype the CRT and aboveground agronomic traits in different field environments. We found that root traits were significantly and positively correlated with most aboveground agronomic traits, including flowering time, plant architecture and grain yield. Using a genome-wide association study (GWAS) coupled with resequencing, a total of 115 associated loci and 22 high-confidence candidate genes were identified for CRT. Approximately one-third of the genetic variation in crown root was co-located with 46 QTLs derived from flowering and plant architecture. Furthermore, 103 (89.6%) of 115 crown root loci were located within known domestication- and/or improvement-selective sweeps, suggesting that crown roots might experience indirect selection in maize during domestication and improvement. Furthermore, the expression of Zm00001d036901, a high-confidence candidate gene, may contribute to the phenotypic variation in maize crown roots, and Zm00001d036901 was selected during the domestication and improvement of maize. This study promotes our understanding of the genetic basis of root architecture and provides resources for genomics-enabled improvements in maize root architecture.

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.

STUDY OF AGRONOMIC AND IMMUNOLOGICAL TRAITS OF NEW FACULTATIVE AND WINTER WHEAT CULTIVAR SAMPLES

This study presents the research on economically valuable traits of 70 varieties of Facultative and Winter Wheat Observation Nursery for Semiarid Environments (FAWWON-SA) received from the International Wheat and Maize Improvement Center (CIMMYT). The study of agronomic and immunological characteristics of plants under field conditions is of great importance in breeding since it allows a selection of the best genotypes more effectively, identifies and uses the sources of valuable traits and increases the accuracy of breeding. The results showed that 57 cultivar samples were winter-hardy, and the days to maturation ranged from 242 to 247. The mass of 1000 kernel ranged from 45.00 to 97.33 grams being coarse and fulfilled. Under artificial infection background of rusts, 15 cultivar samples were resistant to stem, leaf and yellow rusts. Based on the results, wheat cultivar samples were grouped by agronomic and immunological traits, resulting in the identification of 41 cultivar samples with valuable characteristics which recommended as donors in breeding.

Estimating the genetic parameters of yield-related traits under different nitrogen conditions in maize.

Understanding the genetic basis responding to nitrogen (N) fertilization in crop production is a long-standing research topic in plant breeding and genetics. Albeit years of continuous efforts, the genetic architecture parameters, such as heritability, polygenicity, and mode of selection, underlying the N responses in maize remain largely unclear. In this study, about n = 230 maize inbred lines were phenotyped under high N (HN) and low N (LN) conditions for 2 consecutive years to obtain 6 yield-related traits. Heritability analyses suggested that traits highly responsive to N treatments were less heritable. Using publicly available SNP genotypes, the genome-wide association study (GWAS) was conducted to identify n = 237 and n = 130 trait-associated loci under HN and LN conditions, n = 164 for N-responsive (NR) traits, and n = 31 for genotype by N interaction (G × N). Furthermore, genome-wide complex trait Bayesian (GCTB) analysis, a method complementary to GWAS, was performed to estimate genetic parameters, including genetic polygenicity and the mode of selection (S). GCTB results suggested that the NR value of a yield component trait was highly polygenic and that 4 NR traits exhibited negative correlations between SNP effects and their minor allele frequencies (or the S value <0)-a pattern consistent with negative selection to purge deleterious alleles. This study reveals the complex genetic architecture underlying N responses for yield-related traits and provides candidate genetic loci for N resilient maize improvement.