Rind Penetrometer Resistance Research Articles

An integrated QTL mapping and transcriptome sequencing provides further molecular insights and candidate genes for stem strength in rapeseed (Brassica napus L.).

We detected the major QTL- qSR.A07, which regulated stem strength and was fine-mapped to 490 kb. BnaA07G0302800ZS and BnaA07G0305700ZS as the candidate functional genes were identified at qSR.A07 locus. The stem's mechanical properties reflect its ability to resist lodging. In rapeseed (Brassica napus L.), although stem lodging negatively affects yield and generates harvesting difficulties, the molecular regulation of stem strength remains elusive. Hence, this study aimed to unravel the main loci and molecular mechanisms governing rapeseed stem strength. A mapping population consisting of 267 RILs (recombinant inbred lines) was developed from the crossed between ZS11 (high stem strength) and 4D122 (low stem strength), and two mechanical properties of stems including stem breaking strength and stem rind penetrometer resistance were phenotyped in four different environments. Four pleiotropic QTLs that were stable in at least two environments were detected. qSR.A07, the major one, was fine-mapped to a 490kb interval between markers SA7-2711 and SA7-2760 on chromosome 7. It displayed epistatic interaction with qRPR.A09-2. Comparative transcriptome sequencing and analysis unveiled methionine/S-adenosylmethionine cycle (Met/SAM cycle), cytoskeleton organization, sulfur metabolism and phenylpropanoid biosynthesis as the main pathways associated with high stem strength. Further, we identified two candidate genes, BnaA07G0302800ZS and BnaA07G0305700ZS, at qSR.A07 locus. Gene sequence alignment identified a number of InDels, SNPs and amino acid variants in sequences of these genes between ZS11 and 4D122. Finally, based on these genetic variants, we developed three SNP markers of these genes to facilitate future genetic selection and functional studies. These findings offer important genetic resources for the molecular-assisted breeding of novel rapeseed stem lodging-resistant varieties.

Genome-wide association study for stalk lodging resistance related traits in maize (Zea mays L.)

BackgroundThe stalk traits stalk diameter, stalk length, rind penetrometer resistance and dry matter content are important indicators for measuring lodging resistance.ResultsIn this study, 377 inbred lines were used as the basic materials, and four stalk-related traits including stalk diameter, stalk length, rind penetrometer resistance and dry matter content of the third segment of maize, were investigated at the tasseling, grain filling, and maturity stages. 461,053 high-quality SNPs which were obtained by whole genome resequencing were used for genome-wide association study. As a result of mixed linear model analysis (P < 9.77 × 10–6), 29 significant SNPs related to traits were detected, accounting for 7.19% -15.03% of phenotypic variation, among which 4, 1, 4 and 20 SNPs were found related to rind penetrometer resistance, stalk diameter, stalk length, and dry matter content respectively. Most candidate genes are related to plant element structure, signal transduction mechanisms, inorganic ion transport and metabolism, nucleotide transport and metabolism, and transporter enzyme families. Comparing mixed linear model with generalized linear model, a total of 12 candidate genes were detected repeatedly, during which the candidate gene Zm00001d014449 were detected 5 times, with a phenotypic variation interpretation rate of 9.95% -10.84%. This gene is mainly expressed in cells with active cell division and tissue differentiation, and is involved in the formation of stalk vascular bundles and the synthesis of cell walls. Another candidate gene, Zm00001d005300, encodes the transcription factor MYB44, which regulates the dependence of salt stress signal phosphorylation, can effectively inhibit the accumulation of destructive reactive oxygen species, and has a certain resistance to non-biotic stress. In addition, this study also found that 10 unknown functional genes can be further Functional verification.ConclusionsThis study helps to deepen the understanding of the genetic basis of traits related to maize stalk lodging resistance, and provides theoretical guidance for future maize lodging resistance breeding.

Genetic basis of maize stalk strength decoded via linkage and association mapping.

Stalk lodging is a severe problem that limits maize production worldwide, although little attention has been given to its genetic basis. Here we measured rind penetrometer resistance (RPR), an effective index for stalk lodging, in a multi-parent population of 1948 recombinant inbred lines (RILs) and an association population of 508 inbred lines (AMP508). Linkage and association mapping identified 53 and 29 single quantitative trait loci (QTLs) and 50 and 19 pairs of epistatic interactions for RPR in the multi-parent population and AMP508 population, respectively. Phenotypic variation explained by all identified epistatic QTLs (up to ~5%) was much less than that explained by all single additive QTLs (up to ~33% in the multi-parent population and ~ 60% in the AMP508 population). Among all detected QTLs, only eight single QTLs explained >10% of phenotypic variation in single RIL populations. Alleles that increased RPR were enriched in tropical/subtropical (TST) groups from the AMP508 population. Based on genome-wide association studies in both populations, we identified 137 candidate genes affecting RPR, which were assigned to multiple biological processes, such as the biosynthesis of cell wall components. Sixty-six candidate genes were cross-validated by multiple methods or populations. Most importantly, 23 candidate genes were upregulated or downregulated in high-RPR lines relative to low-RPR lines, supporting the associations between candidate genes and RPR. These findings reveal the complex nature of the genetic basis underlying RPR and provide loci or candidate genes for developing elite varieties that are resistant to stalk lodging via molecular breeding.

A high-throughput phenotyping method for sugarcane rind penetrometer resistance and breaking force characterization by near-infrared spectroscopy

BackgroundSugarcane (Saccharum spp.) is the core crop for sugar and bioethanol production over the world. A major problem in sugarcane production is stalk lodging due to weak mechanical strength. Rind penetrometer resistance (RPR) and breaking force are two kinds of regular parameters for mechanical strength characterization. However, due to the lack of efficient methods for determining RPR and breaking force in sugarcane, genetic approaches for improving these traits are generally limited. This study was designed to use near-infrared spectroscopy (NIRS) calibration assay to accurately assess mechanical strength on a high-throughput basis for the first time.ResultsBased on well-established laboratory measurements of sugarcane stalk internodes collected in the years 2019 and 2020, considerable variations in RPR and breaking force were observed in the stalk internodes. Following a standard NIRS calibration process, two online models were obtained with a high coefficient of determination (R2) and the ratio of prediction to deviation (RPD) values during calibration, internal cross-validation, and external validation. Remarkably, the equation for RPR exhibited R2 and RPD values as high as 0.997 and 17.70, as well as showing relatively low root mean square error values at 0.44 N mm−2 during global modeling, demonstrating excellent predictive performance.ConclusionsThis study delivered a successful attempt for rapid and precise prediction of rind penetrometer resistance and breaking force in sugarcane stalk by NIRS assay. These established models can be used to improve phenotyping jobs for sugarcane germplasm on a large scale.

Integrating biochemical and anatomical characterizations with transcriptome analysis to dissect superior stem strength of ZS11 (Brassica napus).

Stem lodging resistance is a serious problem impairing crop yield and quality. ZS11 is an adaptable and stable yielding rapeseed variety with excellent resistance to lodging. However, the mechanism regulating lodging resistance in ZS11 remains unclear. Here, we observed that high stem mechanical strength is the main factor determining the superior lodging resistance of ZS11 through a comparative biology study. Compared with 4D122, ZS11 has higher rind penetrometer resistance (RPR) and stem breaking strength (SBS) at flowering and silique stages. Anatomical analysis shows that ZS11 exhibits thicker xylem layers and denser interfascicular fibrocytes. Analysis of cell wall components suggests that ZS11 possessed more lignin and cellulose during stem secondary development. By comparative transcriptome analysis, we reveal a relatively higher expression of genes required for S-adenosylmethionine (SAM) synthesis, and several key genes (4-COUMATATE-CoA LIGASE, CINNAMOYL-CoA REDUCTASE, CAFFEATE O-METHYLTRANSFERASE, PEROXIDASE) involved in lignin synthesis pathway in ZS11, which support an enhanced lignin biosynthesis ability in the ZS11 stem. Moreover, the difference in cellulose may relate to the significant enrichment of DEGs associated with microtubule-related process and cytoskeleton organization at the flowering stage. Protein interaction network analysis indicate that the preferential expression of several genes, such as LONESOME HIGHWAY (LHW), DNA BINDING WITH ONE FINGERS (DOFs), WUSCHEL HOMEOBOX RELATED 4 (WOX4), are related to vascular development and contribute to denser and thicker lignified cell layers in ZS11. Taken together, our results provide insights into the physiological and molecular regulatory basis for the formation of stem lodging resistance in ZS11, which will greatly promote the application of this superior trait in rapeseed breeding.

Identification of quantitative trait loci for related traits of stalk lodging resistance using genome-wide association studies in maize (Zea mays L.)

BackgroundStalk lodging is one of the main factors affecting maize (Zea mays L.) yield and limiting mechanized harvesting. Developing maize varieties with high stalk lodging resistance requires exploring the genetic basis of lodging resistance-associated agronomic traits. Stalk strength is an important indicator to evaluate maize lodging and can be evaluated by measuring stalk rind penetrometer resistance (RPR) and stalk buckling strength (SBS). Along with morphological traits of the stalk for the third internodes length (TIL), fourth internode length (FIL), third internode diameter (TID), and the fourth internode diameter (FID) traits are associated with stalk lodging resistance.ResultsIn this study, a natural population containing 248 diverse maize inbred lines genotyped with 83,057 single nucleotide polymorphism (SNP) markers was used for genome-wide association study (GWAS) for six stalk lodging resistance-related traits. The heritability of all traits ranged from 0.59 to 0.72 in the association mapping panel. A total of 85 significant SNPs were identified for the association mapping panel using best linear unbiased prediction (BLUP) values of all traits. Additionally, five candidate genes were associated with stalk strength traits, which were either directly or indirectly associated with cell wall components.ConclusionsThese findings contribute to our understanding of the genetic basis of maize stalk lodging and provide valuable theoretical guidance for lodging resistance in maize breeding in the future.

Characterization and Fine Mapping of qRPR1-3 and qRPR3-1, Two Major QTLs for Rind Penetrometer Resistance in Maize.

Stalk strength is one of the most important traits in maize, which affects stalk lodging resistance and, consequently, maize harvestable yield. Rind penetrometer resistance (RPR) as an effective and reliable measurement for evaluating maize stalk strength is positively correlated with stalk lodging resistance. In this study, one F2 and three F2:3 populations derived from the cross of inbred lines 3705I (the low RPR line) and LH277 (the high RPR line) were constructed for mapping quantitative trait loci (QTL), conferring RPR in maize. Fourteen RPR QTLs were identified in four environments and explained the phenotypic variation of RPR from 4.14 to 15.89%. By using a sequential fine-mapping strategy based on the progeny test, two major QTLs, qRPR1-3 and qRPR3-1, were narrowed down to 4-Mb and 550-kb genomic interval, respectively. The quantitative real-time PCR (qRT-PCR) assay was adopted to identify 12 candidate genes responsible for QTL qRPR3-1. These findings should facilitate the identification of the polymorphism loci underlying QTL qRPR3-1 and molecular breeding for RPR in maize.

Genome-wide association study identifies novel candidate loci or genes affecting stalk strength in maize

Stalk strength increases resistance to stalk lodging, which causes maize (Zea mays L.) production losses worldwide. The genetic mechanisms regulating stalk strength remain unclear. In this study, three stalk strength-related traits (rind penetrometer resistance, stalk crushing strength, and stalk bending strength) and four plant architecture traits (plant height, ear height, stem diameter, stem length) were measured in three field trials. Substantial phenotypic variation was detected for these traits. A genome-wide association study (GWAS) was conducted using general and mixed linear models and 372,331 single-nucleotide polymorphisms (SNPs). A total of 94 quantitative trait loci including 241 SNPs were detected. By combining the GWAS data with public gene expression data, 56 candidate genes within 50 kb of the significant SNPs were identified, including genes encoding flavonol synthase (GRMZM2G069298, ZmFLS2), nitrate reductase (GRMZM5G878558, ZmNR2), glucose-1-phosphate adenylyltransferase (GRMZM2G027955), and laccase (GRMZM2G447271). Resequencing GRMZM2G069298 and GRMZM5G878558 in all tested lines revealed respectively 47 and 2 variants associated with RPR. Comparison of the RPR of the zmnr2 EMS mutant and the wild-type plant under high- and low-nitrogen conditions verified the GRMZM5G878558 function. These findings may be useful for clarifying the genetic basis of stalk strength. The identified candidate genes and variants may be useful for the genetic improvement of maize lodging resistance.

Genetic Architecture of Maize Stalk Diameter and Rind Penetrometer Resistance in a Recombinant Inbred Line Population.

Stalk lodging presents a major constraint on maize (Zea mays L.) quantity and quality and hampers mechanized grain harvesting. Stalk diameter (SD) and rind penetrometer resistance (RPR) are crucial indicators of stalk lodging. To dissect the genetic architecture of these indicators, we constructed a recombinant inbred line (RIL) population derived from a cross between maize inbred lines LDC-1 and YS501 to identify quantitative trait loci (QTLs) controlling SD and RPR. Corresponding phenotypes of basal second, third, and fourth internodes in four environments were determined. By integrating QTL mapping results based on individual environments and best linear unbiased prediction (BLUP) values, we identified 12, 12, and 13 QTLs associated with SD and 17, 14, and 17 associated with RPR. Each QTL accounted for 3.83–21.72% of phenotypic variation. For SD-related QTLs, 30 of 37 were enriched in 12 QTL clusters; similarly, RPR-related QTLs had 38 of 48 enriched in 12 QTL clusters. The stable QTL qSD9-2 for SD on chromosome 9 was validated and delimited within a physical region of 9.97 Mb. Confidence intervals of RPR-related QTLs contained 169 genes involved in lignin and polysaccharide biosynthesis, with 12 of these less than 500 kb from the peak of the corresponding QTL. Our results deepen our understanding of the genetic mechanism of maize stalk strength and provide a basis for breeding lodging resistance.

Transcriptome analysis reveals the mechanism of internode development affecting maize stalk strength

BackgroundThe stalk rind is one of the important factors affecting maize stalk strength that is closely related to stalk lodging. However, the mechanism of rind development in maize is still largely unknown.ResultsIn this study, we analyzed the mechanical, anatomical, and biochemical properties of the third basal internode in one maize non-stiff-stalk (NSS) line and two stiff-stalk (SS) lines. Compared with the NSS line, the two SS lines had a significantly higher rind penetrometer resistance, thicker rind, and higher dry matter, hemicellulose, cellulose, and lignin weights per unit length. RNA-seq analysis was used to compare transcriptomes of the third basal internode of the two SS lines and the NSS line at the ninth leaf and tasseling stages. Gene Ontology (GO) enrichment analysis revealed that genes involved in hydrolase activity (hydrolyzing O-glycosyl compounds) and cytoskeleton organization were significantly up-regulated in the two SS lines at the ninth leaf stage and that microtubule process-related genes were significantly up-regulated in the two SS lines at the tasseling stage. Moreover, the two SS lines had enhanced expression of cell wall metabolism-related genes at the tasseling stage.ConclusionsThe synthesis of cell wall polysaccharides and the cytoskeleton might play important roles in internode development. Our results can be applied for screening lodging-resistant inbred lines and breeding lodging-resistant cultivars in maize.

Genetic Architecture of Maize Rind Strength Revealed by the Analysis of Divergently Selected Populations.

The strength of the stalk rind, measured as rind penetrometer resistance (RPR), is an important contributor to stalk lodging resistance. To enhance the genetic architecture of RPR, we combined selection mapping on populations developed by 15 cycles of divergent selection for high and low RPR with time-course transcriptomic and metabolic analyses of the stalks. Divergent selection significantly altered allele frequencies of 3,656 and 3,412 single- nucleotide polymorphisms (SNPs) in the high and low RPR populations, respectively. Surprisingly, only 110 (1.56%) SNPs under selection were common in both populations, while the majority (98.4%) were unique to each population. This result indicated that high and low RPR phenotypes are produced by biologically distinct mechanisms. Remarkably, regions harboring lignin and polysaccharide genes were preferentially selected in high and low RPR populations, respectively. The preferential selection was manifested as higher lignification and increased saccharification of the high and low RPR stalks, respectively. The evolution of distinct gene classes according to the direction of selection was unexpected in the context of parallel evolution and demonstrated that selection for a trait, albeit in different directions, does not necessarily act on the same genes. Tricin, a grass-specific monolignol that initiates the incorporation of lignin in the cell walls, emerged as a key determinant of RPR. Integration of selection mapping and transcriptomic analyses with published genetic studies of RPR identified several candidate genes including ZmMYB31, ZmNAC25, ZmMADS1, ZmEXPA2, ZmIAA41 and hk5. These findings provide a foundation for an enhanced understanding of RPR and the improvement of stalk lodging resistance.

Identification of traits and genes associated with lodging resistance in maize

Lodging is a major problem limiting maize yield worldwide. However, the mechanisms of lodging resistance remain incompletely understood for maize. Here, we evaluated 443 maize accessions for lodging resistance in the field. Five lodging-resistant accessions and five lodging-sensitive accessions were selected for further research. The leaf number, plant height, stem diameter, and rind penetrometer resistance were similar between lodging-resistant and -sensitive inbred lines. The average thickness of sclerenchymatous hypodermis layer was thicker and the vascular area was larger in the lodging-resistant lines compared with lodging-sensitive lines. Although total lignin content in stem tissue did not significantly differ between lodging-resistant and -sensitive lines, phloroglucinol staining revealed that the lignin content of the cell wall in the stem cortex and in the stem vascular tissue near the cortex was higher in the lodging-resistant lines than in the lodging-sensitive lines. Analysis of strand-specific RNA-seq transcriptome showed that a total of 793 genes were up-regulated and 713 genes were down-regulated in lodging-resistant lines relative to lodging-sensitive lines. The up-regulated genes in lodging-resistant lines were enriched in cell wall biogenesis. These results indicated that modification of cell wall biosynthesis would contribute to lodging resistance of maize.

Selection for yield and its component traits in interspecific recombinant inbred lines of tef

Forty recombinant inbred lines (RILs) of interspecific cross of Eragrostis tef x E. pilosa were evaluated to study variability and interrelationships among agronomic traits using randomized complete block design. The RILs were evaluated for 17 traits. The result showed panicle length, rind penetrometer resistance of the first and the second basal internodes, 100-kernel weight, kernel weight per panicle, plant height and grain yield per plant had high estimates of genetic coefficient of variation, broad sense heritability and genetic advance. Thus, improvement of these traits could be attained through direct selection without the masking effect of the environment. The correlation study showed positive and significant (p&lt;0.01) phenotypic and genotypic associations of grain yield per plant with days to heading and maturity, panicle length, 100-kernel weight, kernel weight per panicle, biomass yield per plant and harvest index. Genotypic path coefficient analysis revealed that panicle length, biomass yield per plant, crushing strength of the second basal internode, harvest index, days to heading and kernel weight per panicle exerted appreciable positive direct effect on grain yield per plant. These traits could, therefore, be considered as indirect selection criteria while selecting lines in order to improve grain yield of the interspecific population.

Genome-wide prediction in a hybrid maize population adapted to Northwest China

Genome-wide prediction is a promising approach to boost selection gain in hybrid breeding. Our main objective was to evaluate the potential and limits of genome-wide prediction to identify superior hybrid combinations adapted to Northwest China. A total of 490 hybrids derived from crosses among 119 inbred lines from the Shaan A and Shaan B heterotic pattern were used for genome-wide prediction of ten agronomic traits. We tested eight different statistical prediction models considering additive (A) effects and in addition evaluated the impact of dominance (D) and epistasis (E) on the prediction ability. Employing five-fold cross validation, we show that the average prediction ability ranged from 0.386 to 0.794 across traits and models. Six parametric methods, i.e. ridge regression, LASSO, Elastic Net, Bayes B, Bayes C and reproducing kernel Hilbert space (RKHS) approach, displayed a very similar prediction ability for each trait and two non-parametric methods (random forest and support vector machine) had a higher prediction performance for the trait rind penetrometer resistance of the third internode above ground (RPR_TIAG). The models of A + D RKHS and A + D + E RKHS were slightly better for predicting traits with a relatively high non-additive variance. Integrating trait-specific markers into the A + D RKHS model improved the prediction ability of grain yield by 3%, from 0.528 to 0.558. Of all 6328 potential hybrids, selection of the top 44 hybrids would lead to a 6% increase in grain yield compared with Zhengdan 958, a commercially successful hybrid variety. In conclusion, our results substantiate the value of genome-wide prediction for hybrid breeding and suggest dozens of promising single crosses for developing high-yielding hybrids for Northwest China.

Genetic mapping and genomic selection for maize stalk strength

BackgroundMaize is one of the most important staple crops and is widely grown throughout the world. Stalk lodging can cause enormous yield losses in maize production. However, rind penetrometer resistance (RPR), which is recognized as a reliable measurement to evaluate stalk strength, has been shown to be efficient and useful for improving stalk lodging-resistance. Linkage mapping is an acknowledged approach for exploring the genetic architecture of target traits. In addition, genomic selection (GS) using whole genome markers enhances selection efficiency for genetically complex traits. In the present study, two recombinant inbred line (RIL) populations were utilized to dissect the genetic basis of RPR, which was evaluated in seven growth stages.ResultsThe optimal stages to measure stalk strength are the silking phase and stages after silking. A total of 66 and 45 quantitative trait loci (QTL) were identified in each RIL population. Several potential candidate genes were predicted according to the maize gene annotation database and were closely associated with the biosynthesis of cell wall components. Moreover, analysis of gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway further indicated that genes related to cell wall formation were involved in the determination of RPR. In addition, a multivariate model of genomic selection efficiently improved the prediction accuracy relative to a univariate model and a model considering RPR-relevant loci as fixed effects.ConclusionsThe genetic architecture of RPR is highly genetically complex. Multiple minor effect QTL are jointly involved in controlling phenotypic variation in RPR. Several pleiotropic QTL identified in multiple stages may contain reliable genes and can be used to develop functional markers for improving the selection efficiency of stalk strength. The application of genomic selection to RPR may be a promising approach to accelerate breeding process for improving stalk strength and enhancing lodging-resistance.

Stalk Bending Strength is Strongly Associated with Maize Stalk Lodging Incidence Across Multiple Environments

Stalk lodging in maize results in substantial yield losses worldwide. These losses could be prevented through genetic improvement. However, breeding efforts and genetics studies are hindered by lack of a robust and economical phenotyping method for assessing stalk lodging resistance. A field-based phenotyping platform that induces failure patterns consistent with natural stalk lodging events and measures stalk bending strength in field-grown plants was recently developed. Here we examine the association between data gathered from this new phenotyping platform with counts of stalk lodging incidence on 47 maize hybrids representing a subset of genetic diversity. For comparative purposes, we examine four additional predictive phenotypes commonly assumed to be related to stalk lodging resistance; namely, rind penetrometer resistance (a.k.a. rind puncture resistance), cellulose, hemicellulose, and lignin. Lodging incidence data were gathered on 47 hybrids, grown in 98 distinct environments, spanning four years and 41 unique geographical locations in North America. Using Bayesian generalized linear mixed effects models, we show that stalk lodging incidence is associated with each of the five predictive phenotypes. Further, based on a joint analysis we demonstrate that, among the phenotypes considered, stalk bending strength measured by the new phenotyping platform is the strongest predictive phenotype of naturally occurring stalk lodging incidence in maize, followed by rind penetrometer resistance and cellulose content. This study demonstrates that field-based measurements of stalk bending strength provide a reliable estimate of stalk lodging incidence. The stalk bending strength data acquired from the new phenotyping platform will be valuable for phenotypic selection in breeding programs and for generating mechanistic insights into the genetic regulation of stalk lodging resistance.

Genetic dissection of stalk lodging-related traits using an IBM Syn10 DH population in maize across three environments (Zea mays L.).

Stalk lodging severely limits the grain yield of maize (Zea mays L.). Mechanical stalk strength can be reflected by the traits of stalk diameter (SD), stalk bending strength (SBS), and lodging rind penetrometer resistance (RPR). To determine the genetic basis of maize stalk lodging, quantitative trait loci (QTLs) were mapped for these three traits using the IBM Syn10 DH population in three environments. The results indicated that there were strong genetic correlations among the three traits, and the analyses of phenotypic variations for SD, SBS, and RPR across the three environments showed high broad-sense heritability (0.6843, 0.5175, and 0.7379, respectively). In total, 44 significant QTLs were identified control the above traits across the 3 environments. A total of 14, 14, and 16 QTLs were identified for SD, SBS, and RPR across single-environment mapping, respectively. Notably, ten QTLs were stably expressed across multiple-environments, including two QTLs for SD, three for SBS, and five for RPR. Three major QTLs each accounting for over 10% of the phenotypic variation were qSD6-2 (10.03%), qSD8-2 (13.73%), and qSBS1-2 (11.89%). Comprehensive analysis of all QTLs in this study revealed that 5 QTL clusters including 12 QTLs were located on chromosomes 1, 3, 7, and 8, respectively. Among these 44 QTLs, 9 harbored 13 stalk lodging-associated SNPs that were detected by our recently published work, with 1 SNP successfully validated in the IBM Syn10 DH population. These chromosomal regions will be useful for marker-assisted selection and fine mapping of stalk lodging-related traits in maize.

Multi-Locus Genome-Wide Association Study Reveals the Genetic Architecture of Stalk Lodging Resistance-Related Traits in Maize.

Stalk lodging resistance, which is mainly measured by stem diameter (SD), stalk bending strength (SBS), and rind penetrometer resistance (RPR) in maize, seriously affects the yield and quality of maize (Zea mays L.). To dissect its genetic architecture, in this study multi-locus genome-wide association studies for stalk lodging resistance-related traits were conducted in a population of 257 inbred lines, with tropical, subtropical, and temperate backgrounds, genotyped with 48,193 high-quality single nucleotide polymorphisms. The analyses of phenotypic variations for the above traits in three environments showed high broad-sense heritability (0.679, 0.720, and 0.854, respectively). In total, 423 significant Quantitative Trait Nucleotides (QTNs) were identified by mrMLM, FASTmrEMMA, ISIS EM-BLASSO, and pLARmEB methods to be associated with the above traits. Among these QTNs, 29, 34, and 48 were commonly detected by multiple methods or across multiple environments to be related to SD, SBS, and RPR, respectively. The superior allele analyses in 30 elite lines showed that only eight lines contained more than 50% of the superior alleles, indicating that stalk lodging resistance can be improved by the integration of more superior alleles. Among sixty-three candidate genes of the consistently expressed QTNs, GRMZM5G856734 and GRMZM2G116885, encoding membrane steroid-binding protein 1 and cyclin-dependent kinase inhibitor 1, respectively, possibly inhibit cell elongation and division, which regulates lodging resistance. Our results provide the further understanding of the genetic foundation of maize lodging resistance.

MicroRNA528 Affects Lodging Resistance of Maize by Regulating Lignin Biosynthesis under Nitrogen-Luxury Conditions

Lodging under nitrogen (N)-luxury conditions substantially reduces crop yield and seed quality. However, the molecular mechanisms of plant lodging resistance remain largely unclear, especially in maize. We report here that the expression of ZmmiR528, a monocot-specific microRNA, is induced by N luxury but reduced by N deficiency. We show by the thioacidolysis and acetyl bromide analysis that N luxury significantly reduces the generation of H, G, and S monomers of the lignin as well as its total content in maize shoots. We further demonstrate that ZmLACCASE3 (ZmLAC3) and ZmLACCASE5 (ZmLAC5), which encode the copper-containing laccases, are the targets of ZmmiR528. In situ hybridization showed that ZmmiR528 is mainly expressed in maize vascular tissues. Knockdown of ZmmiR528 or overexpression of ZmLAC3 significantly increased the lignin content and rind penetrometer resistance of maize stems. In contrast, transgenic maize plants overexpressing ZmmiR528 had reduced lignin content and rind penetrometer resistance and were prone to lodging under N-luxury conditions. RNA-sequencing analysis revealed that ZmPAL7 and ZmPAL8 are upregulated in transgenic maize lines downregulating ZmmiR528. Under N-luxury conditions, the expression levels of ZmPALs were much higher in ZmmiR528-knockdown lines than in the wild type and transgenic maize lines overexpressing ZmmiR528. Taken together, these results indicate that, by regulating the expression of ZmLAC3 and ZmLAC5, ZmmiR528 affects maize lodging resistance under N-luxury conditions.

Ploidy effect and genetic architecture exploration of stalk traits using DH and its corresponding haploid populations in maize

BackgroundDoubled haploid (DH) lines produced via in vivo haploid induction have become indispensable in maize research and practical breeding, so it is important to understand traits characteristics in DH and its corresponding haploids which derived from each DH lines. In this study, a DH population derived from Zheng58 × Chang7-2 and a haploid population, were developed, genotyped and evaluated to investigate genetic architecture of eight stalk traits, especially rind penetrometer resistance (RPR) and in vitro dry matter digestion (IVDMD), which affecting maize stalk lodging-resistance and feeding values, respectively.ResultsPhenotypic correlation coefficients ranged from 0.38 to 0.69 between the two populations for eight stalk traits. Heritability values of all stalk traits ranged from 0.49 to 0.81 in the DH population, and 0.58 to 0.89 in the haploid population. Quantitative trait loci (QTL) mapping study showed that a total of 47 QTL for all traits accounting for genetic variations ranging from 1.6 to 36.5 % were detected in two populations. One or more QTL sharing common region for each trait were detected between two different ploidy populations. Potential candidate genes predicated from the four QTL support intervals for RPR and IVDMD were indirectly or directly involved with cellulose and lignin biosynthesis, which participated in cell wall formation. The increased expression levels of lignin and cellulose synthesis key genes in the haploid situation illustrated that dosage compensation may account for genome dosage effect in our study.ConclusionsThe current investigation extended understanding about the genetic basis of stalk traits and correlations between DH and its haploid populations, which showed consistence and difference between them in phenotype, QTL characters, and gene expression. The higher heritabilities and partly higher QTL detection power were presented in haploid population than in DH population. All of which described above could lay a preliminary foundation for genetic architecture study with haploid population and may benefit selection in haploid-stage to reduce cost in DH breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0742-3) contains supplementary material, which is available to authorized users.