Allopolyploidization increases genetic recombination in the ancestral diploid D genome during wheat evolution

Genetic recombination produces new allelic combinations,thereby introducing variation for domestication.Allopolyploidization has increased the evolutionary potential of hexaploid common wheat by conferring the advantages of heterosis and gene redundancy,but whether a relationship exists between allopolyploidization and genetic recombination is currently unknown.To study the impact of allopolyploid ization on genetic recombination in the ancestral D genome of wheat,we generated new synthetic hexaploid wheats by crossing tetraploid Triticum turgidum with multiple diploid Aegilops tauschii accessions,with subsequent chromosome doubling,to simulate the evolutionary hexaploidization process.Using the DArT-Seq approach,we determined the genotypes of two new synthetic hexaploid wheats with their parents,F;plants in a diploid population(2 x,D_(1)D_(1)×D_(2)D_(2))and its new synthetic hexaploid wheatderived population(6 x,AABBD_(1)D_(1)×AABBD_(2)D_(2)).About 11%of detected SNP loci spanning the D genome of Ae.tauschii were eliminated after allohexaploidization,and the degree of segregation distortion was increased in their hexaploid offspring from the F_(1) generation.Based on codominant genotypes,the mean genetic interval length and recombination frequency between pairs of adjacent and linked SNPs on D genome of the hexaploid F;population were 2.3 fold greater than those in the diploid F_(2) population,and the recombination frequency of Ae.tauschii was increased by their hexaploidization with T.turgidum.In conclusion,allopolyploidization increases genetic recombination of the ancestral diploid D genome of wheat,and DNA elimination and increased segregation distortion also occur after allopolyploidization.Increased genetic recombination could have produced more new allelic combinations subject to natural or artificial selection,helping wheat to spread rapidly to become a major global crop and thereby accelerating the evolution of wheat via hexaploidization.

Integrated Weed Management Through Tillage and Herbicides for Wheat Production in Rice-Wheat Cropping System in Northwestern Pakistan

Conservational tillage （CT） in combination with broad spectrum herbicide may be more efficient and economical in controlling weeds, reducing cost of cultivation, and enhancing wheat yield. Field experiments were carried out to evaluate the effect of tillage and herbicides on weeds and wheat yield under rice-wheat cropping system （RWCS）. The results indicated that broad spectrum herbicides particularly, carfentrazone ethyl ester＋ isoproturon （Affinity 50 WDG） reduced weeds density by 93 and 95% compared to control and also produced the maximum grain yield （6 818 and 6 996 kg ha-l） and HI （harvest index, 44.7 and 44.6%） in 2007-2008 and 2008-2009 growing seasons, respectively. The maximum weeds infestation and the lowest yield were recorded in control. Tillage methods significantly influenced grain yield and HI, while no significant effect on all other parameters. The overall mean yield was significantly higher in zero tillage （5 575 kg ha-l） and reduced tillage （5 584 kg ha-l） compared to CT （5 479 kg ha-^-1）. Besides increasing wheat yield, Affinity 50 WDG and zero tillage are important weed management practices that can be integrated into wheat production in RWCS. However, in case of perennial weeds or insect pests＇ infestation, CT in combination with Affinity 50 WDG would be more productive than conservation tillage.

Sensitivity of durum wheat (Triticum turgidum) to various postemergence herbicides

There are a limited number of herbicide options available for durum wheat production in Ontario, Canada. Four field studies were conducted in Ontario, Canada over a three year period (2008, 2009 and 2010) to evaluate the sensitivity of spring planted durum wheat to post-emergence (POST) applications of dichlorprop/2,4-D, dicamba/ MCPA/mecoprop, clopyralid, bromoxynil/MCPA, pyrasulfotole/bromoxynil, thifensulfuron/tribenuron + MCPA amine, fluroxypyr + MCPA ester, tralkoxydim and fenoxaprop-p-ethyl/safener at the manufacturers’ recommended dose and twice that dose. Visible injury in durum wheat were 0 to 2.4% with dichlorprop/2,4-D, 0 to 6% with dicamba/MCPA/mecoprop, 0 to 0.4% injury with clopyralid, 0 to 1.4% injury with bromoxynil/MCPA, 0 to 3.5% with pyrasulfotole/bromoxynil, 0 to 5% with thifensulfuron/tribenuron + MCPA amine, 0 to 2.6% with fluroxypyr + MCPA ester, 0 to 5% with tralkoxydim and 0.4% to 8% with fenoxaprop-pethyl/safener at various evaluation dates (1, 2, 3 and 4 weeks after treatment). Durum wheat height was decreased as much as 5% with dicamba/ MCPA/mecoprop, 4% with pyrasulfotole/bromoxynil and 6% with fenoxaprop-pethyl/safener but was not affected with other herbicides evaluated. There was no decrease in durum wheat yield with the herbicides evaluated.

Comparative Efficacy of Different Herbicides for Weed Management and Yield Attributes in Wheat

Weed competes with crops for water, nutrients and light so weed infestation is one of the major threats to crop. Present investigation was aimed to asses the comparative efficacy of different herbicides for weed management in wheat crop under agro-climatic conditions of Pakistan. This experiment was laid out in a randomized complete block design (RCBD) design with five replications. Different herbicides were used for weed management in wheat crop. The post emergence application of herbicides included Aim 40 DF @ 0.02 kg a.i. ha-1, Agritop 500 GL-1 @ 0.43 kg a.i. ha-1, Isoproturon 50 WP @ 1 kg a.i. ha-1, Puma super 75 EW @ 0.75 kg, Topik 15 WP @ 0.04 kg and Buctril super 60 EC @ 0.45 kg. For comparison hand weeding and weedy check were also included. In each replication six treatments of these six herbicides were kept. The significantly affected parameters were fresh weed biomass (kg·ha-1), thousand grain weight (g), number of tillers m-2, weed control efficiency (%) and grain yield (kg·ha-1). Statistical analysis showed that maximum weed efficiency (84%) was recorded for Isoproturon 50 WP whereas minimum value (37%) was for Aim 40 DF. Similarly maximum number of tillers m-2 (250) was recorded for Isoproturon 50 WP and minimum (133) in weedy check. The herbicide Isoproturon 50 WP @ 1.0 kg a.i. ha-1 was applied at post emergence performed well and exhibited effectively weed control and better yield in wheat.

Study on the Evolution of Agronomic Traits of Wheat Varieties in Shandong Province in Different Ages

In this study,50 wheat varieties promoted since the founding of the People’s Republic of China in Shandong Province were used as materials to analyze the differences in the agronomic traits between main wheat varieties promoted in different ages.The results showed that in variety replacement process,the plant height decreased significantly,the 1 000-grain weight increased extremely significantly,and the single-stem economic yield and biological yield decreased first and then increased;the economic coefficient increased significantly,and the ear length,number of grains per ear,total number of spikelets and number of fertile spikelets had no obvious trends in the past few decades;and the changes in single-stem biological yield and economic yield were not consistent with the trend in yield per unit area,indicating that coordinating the relationship between population yield and individual yield is an important direction to improve yield.

Genome sequencing reveals the evolution and pathogenic mechanisms of the wheat sharp eyespot pathogen Rhizoctonia cerealis

The necrotrophic fungus Rhizoctonia cerealis is the causal agent of devastating diseases of cereal crops including wheat(Triticum aestivum).We present a high-quality genome assembly of R.cerealis Rc207,a virulent strain causing wheat sharp eyespot.The assembly(56.36 Mb)is composed of 17.87%repeat sequences and 14,433 predicted protein-encoding genes.The Rc207 genome encodes a large and diverse set of genes involved in pathogenicity,especially rich in those encoding secreted proteins,carbohydrateactive enzymes(CAZymes),peptidases,nucleases,cytochrome P450,and secondary metabolismassociated enzymes.Most secretory protein-encoding genes,including CAZymes,peroxygenases,dehydrogenases,and cytochrome P450,were up-regulated during fungal infection of wheat.We identified 831 candidate secretory effectors and validated the functions of 10 up-regulated candidate effector proteins.Of them,nine were confirmed as necrotrophic pathogen’s effectors promoting fungal infection.Abundant potential mobile or plastic genomic regions rich in repeat sequences suggest their roles in fungal adaption and virulence-associated genomic evolution.This study provides valuable resources for further comparative and functional genomics on important fungal pathogens,and provides essential tools for development of effective disease control strategies.

Analysis on evolution of wheat variety in Henan

The essential factor that affects wheat production is variety. The paper reviews the history of fifty seven years since establishment of China about evolution of wheat variety in Henan and divides it into four periods according to historical background and nine generations in terms of developing trend of wheat variety evolution. The analysis on characteristics and influence of wheat variety evolution to wheat production indicates the regulation and contribution of wheat variety evolution, which provides reference for breeding, extending and updating of wheat variety in Henan.

Assessing climate effects on wheat yield heterogeneity in the North China Plain and evolution from 1960 to 2020

This study quantified climate effects on wheat yield heterogeneity in the North China Plain from 1960 to 2020,by integrating the Agricultural Production Systems sIMulator,Optimal Parameters–based Geographical Detector model,and Ensemble Empirical Mode Decomposition model.The factors dominating yield heterogeneity varied by growth stage.For sowing to anthesis,anthesis to maturation,and the entire growth season,minimum temperature,radiation,and vapor pressure deficit has the greatest effect on yield heterogeneity.Interannual periodic oscillations govern the long–term evolution of climate effects on yield heterogeneity from 1960 to 2020.

Study on Genomic Changes in Partial Amphiploids of Common Wheat_Wheatgrass

According to conventional theory, little genomic changes should occur in homozygous and stable amphiploids of the grass family, particularly those involving polyploid wheat as a parent. In the present study, however, extensive genomic changes were detected in two octoploid partial amphiploids of common wheat (Triticum aestivum L.)_wheatgrass (Agropyron intermedium (Host) P.B.=Elytrigia intermedia (Host) Nevski=Thinopyrum intermedium (Host) Barkworth and Dewey), namely Zhong 3 and Zhong 5, by RFLP analysis using 10 low_copy, wheat chromosome_specific sequences and 33 representative homoeologous group_specific sequences as probes. Genomic changes involved loss of wheat hybridization fragment(s) and/or acquisition of new fragment(s). Uniformity of the RFLP patterns among 5 individual plants taken respectively from Zhong 3 and Zhong 5 in two successive generations, suggested that genomic changes probably had occurred in the early few generations after octoploid amphiploid formation, and remained essentially static thereafter. The highly similar RFLP patterns between Zhong 3 and Zhong 5, which had identical genomic constitution but differed from each other due to involvement of different wheat varieties as parents imply that genomic changes were probably not at random. Possible causes for the extensive and rapid genomic changes in the newly formed plant amphiploids, as well as their implications for polyploid genome evolution and breeding application are discussed.

Response of Underseeded Red Clover(Trifolium pratense L.)to Winter Wheat(Triticum aestivum L.)Herbicides as Affected by Application Timing

Underseeding red clover in winter wheat is a beneficial agronomic practice. Still, many growers tend to forgo this approach. One reason is that herbicides used on winter wheat may injure underseeded red clover, reducing its biomass and the subsequent benefits it provides. Therefore, the effect of winter wheat herbicides on underseeded red clover needs to be evaluated. The objectives of this research were to assess the crop tolerance of underseeded red clover to ten winter wheat herbicides used in Ontario, Canada and determine if red clover tolerance differed when the herbicides were applied at various winter wheat growth stages. Experiments were conducted in 2009 and 2010 at four different Ontario locations. Each herbicide treatment was either applied at an early, normal or late timing. Overall, red clover was not affected by herbicides applied at the early timing. The likelihood of herbicides causing injury and reducing biomass of underseeded red clover increased when they were applied at the more advanced winter wheat growth stages. If timing is a constraint, the three herbicides bromoxynil/MCPA, tralkoxydim, and fenoxaprop-pethyl are the safest to use on red clover underseeded to winter wheat. The remaining herbicides 2,4-D, dicamba/MCPA/mecoprop, dichlorprop/2,4-D, thifensulfuron/ tribenuron + MCPA, fluroxypyr + MCPA, pyrasulfotole/bromoxynil, and prosulfuron + bromoxynil are more injurious, with the last two being the most harmful. By having identified the least damaging herbicides on underseeded red clover in winter wheat and the optimal timing for herbicide application, growers are more likely to adopt this beneficial agronomic practice, save on fertilizer costs and improve soil quality.

On the evolution and genetic diversity of the bread wheat D genome

Bread wheat(Triticum aestivum)became a globally dominant crop after incorporating the D genome from the donor species Aegilops tauschii,but the evolutionary history that shaped the D genome during this process remains to be clarified.Here,we propose a renewed evolutionary model linking Ae.tauschii and the hexaploid wheat D genome by constructing an ancestral haplotype map covering 762 Ae.tauschii and hexaploid wheat accessions.We dissected the evolutionary trajectories of Ae.tauschii lineages and reported a few independent intermediate accessions,demonstrating that low-frequency intersublineage gene flow had enriched the diversity of Ae.tauschii.We discovered that the D genome of hexaploid wheat was inherited from a unified ancestral template,but with a mosaic composition that was highly mixed and derived mainly from three Ae.tauschii L2 sublineages located in the Caspian coastal region.This result suggests that early agricultural activities facilitated innovations in D-genome composition and finalized the success of hexaploidization.We found that the majority(51.4%)of genetic diversity was attributed to novel mutations absent in Ae.tauschii,and we identified large Ae.tauschii introgressions from various lineages,which expanded the diversity of the wheat D genome and introduced beneficial alleles.This work sheds light on the process of wheat hexaploidization and highlights the evolutionary significance of the multi-layered genetic diversity of the bread wheat D genome.

A Unique Aegilops tauschii Genotype Needless to Immature Embryo Culture in Cross with Wheat

Common or bread wheat ( Triticum aestivum L., AABBDD, 2n=42) originated ca. 8 000 years ago from hybridization of tetraploid wheat ( Triticum turgidum L., AABB, 2n=28) and diploid Aegilops tauschii Coss. (DD, 2n=14). An essential prerequisite for this evolutionary step is that the natural hybrids between tetraploid wheat and diploid Aegilops tauschii can produce relatively many filled seeds which germinated well. In this study, without special techniques, e.g. immature embryo culture, out of 22 Ae. tauschii accessions, the genotype AS60 produced relatively many filled seeds which germinated well. The seed germination percentages in the crosses of Ae. tauschii ×tetraploid wheat, tetraploid wheat× Ae. tauschii and Ae. tauschii ×common wheat were, respectively, 50.0%, 57.1% and 45.5%. It seems that Ae. tauschii accession AS60 has a unique genotype which facilitate hybrid seed development and viability, and which meets with the prerequisite for wheat evolutionary. Furthermore, the significance of this finding for common wheat improvement and evolution was discussed.

Genetic Differentiation of A and B Chromosomes Between Common Wheat and Wild Emmer as Revealed by RFLP Analysis

To investigate chromosome differentiation of genome A and B between common wheat and wild emmer wheat (Triticum turgidum var. dicoccoides (Koern.) Bowden), the authors conducted a RFLP analysis of the two species using 153 genomic, cDNA and chromosome_specific probes. 75.8% of the probes had detected hybridization polymorphism in at least one of the five restriction enzymes. However, the polymorphic probes were unevenly distributed among different homoeologous groups, between different genomes and in different regions of a single chromosome. Homoeologous group 1 possessed the highest level of polymorphism (96.2%), followed by group 6 and 2 (84.6% and 82.1% respectively). In contrast, only 60%-67% of probes of the other four groups was polymorphic. In most groups the number of probes capable of detecting B chromosome polymorphism was slightly higher than that revealing A chromosome difference (totally 51.8% vs 43.1%). In a single chromosome, RFLP was predominant in the distal region (65.1%) and showed a decreasing trend from the proximal (46.2%) to the pericentric (42.4%) regions. The results suggest that there exists a substantial amount of DNA polymorphism between the A and B chromosomes of common wheat and those of wild emmer wheat, indicating that a considerable degree of genetic differentiation has taken place in the A and B genoms of two species during evolution from wild emmer to common wheat. The extent of the genetic differentiation may vary among different homoeologous groups, between A and B chromosomes and in different regions of individual chromosome.

Characterization of Two Groups of Low_copy and Specific DNA Sequences Isolated from Chromosome 7B of Common Wheat

Recent work revealed that, in the genomes of polyploid wheat, there exists a class of low_copy and chromosome_specific sequences that are labile upon polyploid formation. This class of sequences was proposed to play a critical role in the stabilization and establishment of nascent plant polyploids as new species. To further study this issue, five wheat chromosome 7B_specific sequences, isolated from common wheat (Triticum aestivum L.) by chromosome microdissection, were characterized. The sequences were studied by genomic Southern hybridizations on a collection of polyploid wheats and their diploid progenitors. Four sequences hybridized to all polyploid species, but at the diploid level to only species closely related to the B_genome of polyploid wheat. This indicates that these sequences originated with the divergence of the diploid species, and was then vertically transmitted to polyploids. One sequence hybridized to all species at both the diploid and polyploid levels, suggesting its elimination after the polyploid wheat formation. The hybridization of this sequence to two synthetic polyploid wheats indicated that sequence elimination is a rapid event and probably related to methylation status of the sequence. Based on the above results, we suggest that selective changes of low_copy sequences occur rapidly after polyploid formation, which may contribute to the differentiation of chromosomes in newly formed allopolyploid wheats.

Changes in Root Hydraulic Conductivity During Wheat Evolution

Abstract: A better understanding of the mechanisms of water uptake by plant roots should be vital for improving drought resistance and water use efficiency (WUE). In the present study, we have demonstrated correlations between root system hydraulic conductivity and root characteristics during evolution using six wheat evolution genotypes (solution culture) with different ploidy chromosome sets (Triticum boeoticum Bioss., T. monococcum L.: 2n=2x=14; T. dicoccides Koern., T. dicoccon (Schrank) Schuebl.: 2n = 4x = 28; T. vulgare Vill., T. aestivum L. cv. Xiaoyan No. 6: 2n = 6x = 42). The experimental results showed that significant correlations were found between root system hydraulic conductivity and root characteristics of the materials with the increase in ploidy chromosomes (2x→6x) during wheat evolution. Hydraulic conductivity of the wheat root system at the whole-plant level was increased with chromosome ploidy during evolution, which was positively correlated with hydraulic conductivity of single roots, whole plant biomass, root average diameter, and root growth (length, area), whereas the root/shoot ratio had an inverse correlation with the hydraulic conductivity of root system with increasing chromosome ploidy during wheat evolution. Therefore, it is concluded that that the water uptake ability of wheat roots was strengthened from wild to modern cultivated species during evolution, which will provide scientific evidence for genetic breeding to improve the WUE of wheat by genetic engineering.

Ethylene and Spermidine in Wheat Grains in Relation to Starch Content and Granule Size Distribution Under Water Deficit

Two wheat cultivars （Triticum aestivum L.） were used to evaluate the effects ofpost-anthesis severe water deficit （SD） on starch content and granule size distribution and their relations with ethylene and spermidine （Spd）. Comparison to the well-watered （WW） treatment, SD led to lower Spd and higher 1-aminocylopropane-l-carboxylic acid （ACC） concentrations and ethylene evolution rate （EER） in grains at the critical stage of forming starch granules. Application of Spd or aminoethoxyvinylglycine （AVG） significantly reduced ACC concentration and EER and increased Spd concentration, while ethephon or methylglyoxal-bis （MGBG） had an opposite impact. The volume and surface area distribution of starch granules showed a bimodal curve, while the number distribution exhibited a unimodal curve. SD caused a marked drop in grain weight, grain number and starch content, also led to a significant reduction in the proportion （both by volume and by surface area） of B-type starch granules （〈10 Ixm）, with an increase in those of A-type starch granules （〉10 ~tm）. Application of Spd or AVG increased the proportion （both by volume and by surface area） of B-type starch granules under SD. Correlation analysis suggested that ethylene and Spd showed an antagonism relation in the formation of B-type granules. These results suggested that it would be good for the formation of B-type starch granules to have the physiological traits of higher Spd and lower ACC concentrations and ethylene emission under SD.

Deciphering the evolution and complexity of wheat germplasm from a genomic perspective

Bread wheat provides an essential fraction of the daily calorific intake for humanity.Due to its huge and complex genome,progress in studying on the wheat genome is substantially trailed behind those of the other two major crops,rice and maize,for at least a decade.With rapid advances in genome assembling and reduced cost of high-throughput sequencing,emerging de novo genome assemblies of wheat and whole-genome sequencing data are leading to a paradigm shift in wheat research.Here,we review recent progress in dissecting the complex genome and germplasm evolution of wheat since the release of the first high-quality wheat genome.New insights have been gained in the evolution of wheat germplasm during domestication and modern breeding progress,genomic variations at multiple scales contributing to the diversity of wheat germplasm,and complex transcriptional and epigenetic regulations of functional genes in polyploid wheat.Genomics databases and bioinformatics tools meeting the urgent needs of wheat ge-nomics research are also summarized.The ever-increasing omics data,along with advanced tools and well-structured databases,are expected to accelerate deciphering the germplasm and gene resources in wheat for future breeding advances.

Centromere repositioning and shifts in wheat evolution

The centromere is the region of a chromosome that directs its separation and plays an important role in cell division and reproduction of organisms.Elucidating the dynamics of centromeres is an alternative strategy for exploring the evolution of wheat.Here,we comprehensively analyzed centromeres from the de novoassembled common wheat cultivar Aikang58(AK58),Chinese Spring(CS),and all sequenced diploid and tetraploid ancestors by chromatin immunoprecipitation sequencing,whole-genome bisulfite sequencing,RNA sequencing,assay for transposase-accessible chromatin using sequencing,and comparative genomics.We found that centromere-associated sequences were concentrated during tetraploidization and hexaploidization.Centromeric repeats of wheat(CRWs)have undergone expansion during wheat evolution,with strong interweaving between the A and B subgenomes post tetraploidization.We found that CENH3 prefers to bind with younger CRWs,as directly supported by immunocolocalization on two chromosomes(1A and 2A)of wild emmer wheat with dicentromeric regions,only one of which bound with CENH3.In a comparison of AK58 with CS,obvious centromere repositioning was detected on chromosomes 1B,3D,and 4D.The active centromeres showed a unique combination of lower CG but higher CHH and CHG methylation levels.We also found that centromeric chromatin was more open than pericentromeric chromatin,with higher levels of gene expression but lower gene density.Frequent introgression between tetraploid and hexaploid wheat also had a strong influence on centromere position on the same chromosome.This study also showed that active wheat centromeres were genetically and epigenetically determined.

Change of water use efficiency and its relation with root system growth in wheat evolution

Raising crop water use efficiency (WUE) is the physiological basis to implement crop high efficiently using water. The present soil column and field experiments are designed to investigate the change of wheat WUE (Triticum aestivum L.) at whole plant level and root system growth in evolution and the relationship between WUE and its root system growth using 10 wheat evolution genotypes with different ploidy chromosomes sets. Results show that in wheat evolution from 2n→6n, WUE at whole plant level increases with the increase of ploidy chromosomes, and root system growth (root weight, root length) and root/shoot ratio of wheat decrease with the increase of ploidy chromosomes under dry and irrigated conditions. WUE is negatively correlated with root weight and root/shoot ratio of wheat in evolution, significantly. Root system growth has an adverse redundancy for WUE in wheat evolution, and the root redundancy reduces with the increase of ploidy chromosomes, which result in the increase of wheat WUE at

Herbicide resistance: Development of wheat production systems and current status of resistant weeds in wheat cropping systems

Herbicide resistance in crops has extended the scope of herbicide applications to control weeds. The introduction of herbicide resistant crops resulted in a major shift in the way that herbicides are used in many crops, but not necessarily increased the prevalence of herbicide use, especially in wheat. Wheat is one of the most widely grown crops in the world and currently only two major herbicide-resistant wheat groups have been commercialized to manage weeds in a cost-effective manner. However, sustainable wheat production is threatened by the expanding occurrence of herbicide-resistant weed populations with limited efforts to discover new herbicide molecules. Selective control of certain problematic weeds in wheat was impossible until development and introduction of the technologies, Clearfield and Co AXium Production Systems. However, the current limitations of reliance on specific herbicides and evolution of resistant weeds mandate precautions and considerations when using these systems to prevent the loss of existing herbicide resources and continue sustainable wheat production. The focus of this review is to provide an overview of natural pre-existing herbicide resistance and development of herbicide-resistant technologies in wheat. The mechanisms of resistance to herbicides in wheat as well as the weed populations in wheat cropping systems, and implications for weed management are discussed.