Level ofFusarium infection in wheat spikelets related to location and number of inoculated spores

The flowering time is the most susceptible period for primary infection of wheat heads byFusarium spp. During this period spores can be deposited into the opened wheat florets where they may later cause infections. We quantitatively explored the relationship between variables related to the flowering process and the infection level byFusarium graminearum in single spikelets. We imitated open (chasmogamous) and closed (cleistogamous) flowering by injecting well-defined amounts of spores into and between wheat florets. Applying the spores between the florets resulted in weaker disease symptoms and significantly lower amounts ofFusarium mycotoxins. With larger numbers of spores, the disease symptoms became more pronounced and the mycotoxin amounts per spikelet increased significantly. Our results indicate that the probability of primary infection is approximately proportional to the number of spores reaching the open florets during the flowering process. The breeding of wheat lines which flower partially or completely cleistogamously might reduce theFusarium susceptibility in wheat.     

Genes WHEAT FRIZZY PANICLE and SHAM RAMIFICATION 2 independently regulate differentiation of floral meristems in wheat

Background

Inflorescences of wheat species, spikes, are characteristically unbranched and bear one sessile spikelet at a spike rachis node. Development of supernumerary spikelets (SSs) at rachis nodes or on the extended rachillas is abnormal. Various wheat morphotypes with altered spike morphology, associated with the development of SSs, present an important genetic resource for studies on genetic regulation of wheat inflorescence development.

Results

Here we characterized diploid and tetraploid wheat lines of various non-standard spike morphotypes, which allowed for identification of a new mutant allele of the WHEAT FRIZZY PANICLE (WFZP) gene that determines spike branching in diploid wheat Ttiticum monococcum L. Moreover, we found that the development of SSs and spike branching in wheat T. durum Desf. was a result of a wfzp-A/TtBH-A1 mutation that originated from spontaneous hybridization with T. turgidum convar. сompositum (L.f.) Filat. Detailed characterization of the false-true ramification phenotype controlled by the recessive sham ramification 2 (shr2) gene in tetraploid wheat T. turgidum L. allowed us to suggest putative functions of the SHR2 gene that may be involved in the regulation of spikelet meristem fate and in specification of floret meristems. The results of a gene interaction test suggested that genes WFZP and SHR2 function independently in different processes during spikelet development, whereas another spike ramification gene(s) interact(s) with SHR2 and share(s) common functions.

Conclusions

SS mutants represent an important genetic tool for research on the development of the wheat spikelet and for identification of genes that control meristem activities. Further studies on different non-standard SS morphotypes and wheat lines with altered spike morphology will allow researchers to identify new genes that control meristem identity and determinacy, to elucidate the interaction between the genes, and to understand how these genes, acting in concert, regulate the development of the wheat spike.

     

Phenotypic and genetic analysis of spike and kernel characteristics in wheat reveals long-term genetic trends of grain yield components

Key message

Phenotypic and genetic analysis of six spike and kernel characteristics in wheat revealed geographic patterns as well as long-term trends arising from breeding progress, particularly in regard to spikelet fertility, i.e. the number of kernels per spikelet, a grain yield component that appears to underlie the increase in the number of kernels per spike.

Abstract

Wheat is a staple crop of global relevance that faces continuous demands for improved grain yield. In this study, we evaluated a panel of 407 winter wheat cultivars for six characteristics of spike and kernel development. All traits showed a large genotypic variation and had high heritabilities. We observed geographic patterns for some traits in addition to long-term trends showing a continuous increase in the number of kernels per spike. This breeding progress is likely due to the increase in spikelet fertility, i.e. the number of kernels per spikelet. While the number of kernels per spike and spikelet fertility were significantly positively correlated, both traits showed a significant negative correlation with thousand-kernel weight. Genome-wide association mapping identified only small- and moderate-effect QTL and an effect of the phenology loci Rht-D1 and Ppd-D1 on some of the traits. The allele frequencies of some QTL matched the observed geographic patterns. The quantitative inheritance of all traits with contributions of additional small-effect QTL was substantiated by genomic prediction. Taken together, our results suggest that some of the examined traits were already the basis of grain yield progress in wheat in the past decades. A more targeted exploitation of the available variation, potentially coupled with genomic approaches, may assist wheat breeding in continuing to increase yield levels globally.

     

The chromosome region including the earliness per se locus Eps-Am1 affects the duration of early developmental phases and spikelet number in diploid wheat

Earliness per se genes are those that regulate flowering time independently of vernalization and photoperiod, and are important for the fine tuning of flowering time and for the wide adaptation of wheat to different environments. The earliness per se locus Eps-A(m)1 was recently mapped within a 0.8 cM interval on chromosome 1A(m)L of diploid wheat Triticum monococcum L., and it was shown that its effect was modulated by temperature. In this study, this precise mapping information was used to characterize the effect of the Eps-A(m)1 region on both duration of different developmental phases and spikelet number. Near isogenic lines (NILs) carrying the Eps-A(m)1-l allele from the cultivated accession DV92 had significantly longer vegetative and spike development phases (P<0.0001) than NILs carrying the Eps-A(m)1-e allele from the wild accession G3116. These differences were paralleled by a significant increase in the number of spikelets per spike, in both greenhouse and field experiments (P<0.0001). Significant interactions between temperature and Eps-A(m)1 alleles were detected for heading time (P<0.0001) but not for spikelet number (P=0.67). Experiments using NILs homozygous for chromosomes with recombination events within the 0.8 cM Eps-A(m)1 region showed that the differences in number of spikelets per spike were linked to the differences in heading time controlled by the Eps-A(m)1 locus. These results indicate that the differences in these two traits are either pleiotropic effects of a single gene or the effect of closely linked genes. A similar effect on spikelet number was detected in the distal region of chromosome 1AL in common wheat (T. aestivum L.).     

Premature progression of anther early developmental programs accompanied by comprehensive alterations in transcription during high-temperature injury in barley plants

Kernel number per spike is one of the most important yield components of wheat. To map QTLs related to kernel number including spike length (SPL), spikelet number per spike (SPN), fertile spikelet number (FSPN), sterile spikelet number (SSPN) and compactness, and to characterize the inheritance modes of the QTLs and two-locus interactions, 136 recombinant inbred lines (RILs) derived from ‘Nanda2419’ x ‘Wangshuibai’ and an immortalized F₂ population (IF₂) generated by randomly permutated intermating of these RILs were investigated. QTL mapping made use of the previously constructed over 3300 cM linkage map of the RIL population. Three, five, two, two and six chromosome regions were identified, respectively, for their association with SPL, SPN, FSPN, SSPN, and compactness in at least two of the three environments examined. All compactness QTLs but one shared the respective intervals of QSpn.nau-5A and the SPL QTLs. Xcfd46–Xwmc702 interval on chromosome 7D was related to all traits but SSPN and had consistently the largest effects. The fact that not all the compactness QTL intervals were related to both SPL and SPN indicates that compactness is regulated by different mechanisms. Interval coincidence between QTLs of SPL and SPN and between QTLs of FSPN and SSPN was minimal. For all the traits, favorable alleles exist in both parents. Inheritance modes from additiveness to overdominance of the QTLs were revealed and two-locus interactions were detected, implying that the traits studied are under complex genetic control. The results could contribute to wheat yield improvement and better use of Wangshuibai and Nanda2419 the two special germplasms in wheat breeding program.     

Changes in duration of developmental phases of durum wheat caused by breeding in Spain and Italy during the 20th century and its impact on yield

Background and Aims

Although the apical development of wheat has been widely described, studies analysing how genetic breeding over the 20th century influenced the developmental phases and its consequences on yield generation are lacking, especially for durum wheat under field conditions in Mediterranean environments. The aims of this study were to analyse the effects of breeding in Spain and Italy on crop development during the last century, to determine whether or not breeding significantly altered the developmental phases between sowing and maturity, and to evaluate the importance of each phase in determining the number of grains per spike of durum wheat (Triticum durum) cultivars representing the germplasm grown throughout the 20th century in Spain and Italy.

Methods

Eight field experiments were carried out during 4 years in two contrasting latitudes (Lleida and Granada, Spain). Plant material consisted of 24 durum wheat cultivars (12 Italian and 12 Spanish) grown throughout the 20th century in Spain and Italy.

Key Results

In Spanish materials, breeding reduced the duration of the period from sowing to anthesis, placing the grain-filling period in better conditions. In those cultivars, the sub-phase sowing–terminal spikelet formation was reduced while the duration of the period from booting to anthesis was increased. The number of grains per spike increased by 23 % from old to modern cultivars, by changes in the number of grains per spikelet in both Spanish and Italian cultivars. Floral abortion from booting to anthesis diminished by 24 % from old to modern cultivars, and grain setting increased by 13 %.

Conclusions

The results suggest that breeding reduced not only plant height, but also the time to anthesis. By extending the duration of the phase from booting to anthesis, which was associated with an increase in spike dry weight and grains per spike, it suggests that future increases in spike fertility could be achieved by enlarging that phase.     

Sink-limitation to yield and biomass: a summary of some investigations in spring wheat

Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m‐2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag‐leaf photosynthetic rate during grain‐filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post‐anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain‐filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag‐leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi‐ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.     

A intervarietal genetic map and QTL analysis for yield traits in wheat

A new genetic linkage map was constructed based on recombinant inbred lines (RILs) derived from the cross between the Chinese winter wheat (Triticum aestivum L.) varieties, Chuang 35050 and Shannong 483 (ChSh). The map included 381 loci on all the wheat chromosomes, which were composed of 167 SSR, 94 EST-SSR, 76 ISSR, 26 SRAP, 15 TRAP, and 3 Glu loci. This map covered 3636.7 cM with 1327.7 cM (36.5%), 1485.5 cM (40.9%), and 823.5 cM (22.6%) for A, B, and D genome, respectively, and contained 13 linkage gaps. Using the RILs and the map, we detected 46 putative QTLs on 12 chromosomes for grain yield (GY) per m², thousand-kernel weight (TKW), spike number (SN) per m², kernel number per spike (KNS), sterile spikelet number per spike (SSS), fertile spikelet number per spike (FSS), and total spikelet number per spike (TSS) in four environments. Each QTL explained 4.42–70.25% phenotypic variation. Four QTL cluster regions were detected on chromosomes 1D, 2A, 6B, and 7D. The most important QTL cluster was located on chromosome 7D near the markers of Xwmc31, Xgdm67, and Xgwm428, in which 8 QTLs for TKW, SN, SSS and FSS were observed with very high contributions (27.53–67.63%).     

Successful crossings with early flowering transgenic poplar: interspecific crossings,but not transgenesis,promoted aberrant phenotypes in offspring

In forest tree species, the reproductive phase is reached only after many years or even decades of juvenile growth. Different early flowering systems based on the genetic transfer of heat‐shock promoter driven flowering‐time genes have been proposed for poplar; however, no fertile flowers were reported until now. Here, we studied flower and pollen development in both HSP::AtFT and wild‐type male poplar in detail and developed an optimized heat treatment protocol to obtain fertile HSP::AtFT flowers. Anthers from HSP::AtFT poplar flowers containing fertile pollen grains showed arrested development in stage 12 instead of reaching phase 13 as do wild‐type flowers. Pollen grains could be isolated under the binocular microscope and were used for intra‐ and interspecific crossings with wild‐type poplar. F1‐seedlings segregating the HSP::AtFT gene construct according to Mendelian laws were obtained. A comparison between intra‐ and interspecific crossings revealed that genetic transformation had no detrimental effects on F1‐seedlings. However, interspecific crossings, a broadly accepted breeding method, produced 47% seedlings with an aberrant phenotype. The early flowering system presented in this study opens new possibilities for accelerating breeding of poplar and other forest tree species. Fast breeding and the selection of transgene‐free plants, once the breeding process is concluded, can represent an attractive alternative even under very restrictive regulations.     

The wheat AGL6-like MADS-box gene is a master regulator for floral organ identity and a target for spikelet meristem development manipulation

The AGAMOUS-LIKE6 (AGL6)-like genes are ancient MADS-box genes and are functionally studied in a few model plants. The knowledge of these genes in wheat remains limited. Here, by studying a ‘double homoeolog mutant’ of the AGL6 gene in tetraploid wheat, we showed that AGL6 was required for the development of all four whorls of floral organs with dosage-dependent effect on floret fertility. Yeast two-hybrid analyses detected interactions of AGL6 with all classes of MADS-box proteins in the ABCDE model for floral organ development. AGL6 was found to interact with several additional proteins, including the G protein β and γ (DEP1) subunits. Analysis of the DEP1-B mutant showed a significant reduction in spikelet number per spike in tetraploid wheat, while overexpression of AGL6 in common wheat increased the spikelet number per spike and hence the grain number per spike. RNA-seq analysis identified the regulation of several meristem activity genes by AGL6, such as FUL2 and TaMADS55. Our work therefore extensively updated the wheat ABCDE model and proposed an alternative approach to improve wheat grain yield by manipulating the AGL6 gene.     

Analysis of DNA methylation polymorphism in a set of stable chromosome translocation lines

Interspecific hybridization is associated with the origin of novel traits and confers increased vigor compared with the parent lines, although its molecular basis is poorly understood. We report here the identification of genetic and epigenetic changes in a set of wheat–rye translocation lines (R59, R57, and R25) which exhibited novel heritable morphological characteristics compared with the parent lines (MY11 and L155). Genome in situ hybridization and amplified fragment length polymorphism analyses revealed no obvious variations in the primary structure of the genome in different translocation lines, with the exception of the same 1RS chromosome translocation. Global assessment of the extent and pattern of cytosine methylation alterations by methylation-sensitive amplified polymorphism (MSAP) analyses revealed differences in the extent of genomic DNA methylation between the rye and wheat parent lines. Fully-methylated sites were significantly increased and hemi-methylated sites were markedly decreased in the genome of translocation lines compared with the wheat parental cultivar MY11. Comparisons of different MSAP patterns revealed both monomorphic and polymorphic sites between translocation lines and wheat parents. Sequencing of 44 isolated fragments that showed methylation alterations indicated that cellular genes and especially transposable elements were targets for methylation alterations in translocation lines. The present study provides further understanding of the rules governing the distribution and existence of DNA methylation variations induced in the wheat genome during alien germplasm introduction. Furthermore, our study provides insights into the relationship between DNA methylation and hybrid vigor as well as a theoretical basis for further fundamental research and breeding application.     

Chromosomal Localization of Genes Conferring Desirable Agronomic Traits from Wheat-Agropyron cristatum Disomic Addition Line 5113

Creation of wheat-alien disomic addition lines and localization of desirable genes on alien chromosomes are important for utilization of these genes in genetic improvement of common wheat. In this study, wheat-Agropyron cristatum derivative line 5113 was characterized by genomic in situ hybridization (GISH) and specific-locus amplified fragment sequencing (SLAF-seq), and was demonstrated to be a novel wheat-A. cristatum disomic 6P addition line. Compared with its parent Fukuhokomugi (Fukuho), 5113 displayed multiple elite agronomic traits, including higher uppermost internode/plant height ratio, larger flag leaf, longer spike length, elevated grain number per spike and spikelet number per spike, more kernel number in the middle spikelet, more fertile tiller number per plant, and enhanced resistance to powdery mildew and leaf rust. Genes conferring these elite traits were localized on the A. cristatum 6P chromosome by using SLAF-seq markers and biparental populations (F₁, BC₁F₁ and BC₁F₂ populations) produced from the crosses between Fukuho and 5113. Taken together, chromosomal localization of these desirable genes will facilitate transferring of high-yield and high-resistance genes from A. cristatum into common wheat, and serve as the foundation for the utilization of 5113 in wheat breeding.     

Comprehensive genome and epigenome characterization of CHO cells in response to evolutionary pressures and over time

The most striking characteristic of CHO cells is their adaptability, which enables efficient production of proteins as well as growth under a variety of culture conditions, but also results in genomic and phenotypic instability. To investigate the relative contribution of genomic and epigenetic modifications towards phenotype evolution, comprehensive genome and epigenome data are presented for six related CHO cell lines, both in response to perturbations (different culture conditions and media as well as selection of a specific phenotype with increased transient productivity) and in steady state (prolonged time in culture under constant conditions). Clear transitions were observed in DNA‐methylation patterns upon each perturbation, while few changes occurred over time under constant conditions. Only minor DNA‐methylation changes were observed between exponential and stationary growth phase; however, throughout a batch culture the histone modification pattern underwent continuous adaptation. Variation in genome sequence between the six cell lines on the level of SNPs, InDels, and structural variants is high, both upon perturbation and under constant conditions over time. The here presented comprehensive resource may open the door to improved control and manipulation of gene expression during industrial bioprocesses based on epigenetic mechanisms. Biotechnol. Bioeng. 2016;113: 2241–2253. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.     

A Pyramid Breeding of Eight Grain-yield Related Quantitative Trait Loci Based on Marker-assistant and Phenotype Selection in Rice （Oryza sativa L.）

1000-Grain weight and spikelet number per panicle are two important components for rice grain yield.In our previous study,eight quantitative trait loci(QTLs)conferring spikelet number per panicle and 1000-grain weight were mapped through sequencing-based genotyping of 150 rice recombinant inbred lines(RILs).In this study,we validated the effects of four QTLs from Nipponbare using chromosome segment substitution lines(CSSLs),and pyramided eight grain yield related QTLs.The new lines containing the eight QTLs with positive effects showed increased panicle and spikelet size as compared with the parent variety 93-11.We further proposed a novel pyramid breeding scheme based on marker-assistant and phenotype selection(MAPS).This scheme allowed pyramiding of as many as 24 QTLs at a single hybridization without massive cross work.This study provided insights into the molecular basis of rice grain yield for direct wealth for high-yielding rice breeding.     

基于MAS的小麦抗赤霉病育种材料抗性评价

为了提高黄淮海麦区小麦育种材料的赤霉病抗性,采用分子标记辅助选择的方法,将来自望水白的4个抗赤霉病主效QTL 3B-QTL、4B-QTL、5A-QTL和6B-QTL导入不同的感病背景中,在后代BC1F3和BC1F4株系中评价它们的抗病效应和农艺性状回复情况。结果表明:(1)导入4个抗病QTL株系的平均病小穗率和病粒率分别为12.2%和6.3%,而受体亲本则分别达到59.1%和44.2%,抗病性显著提高;(2)病小穗数和病粒率与穗长及株高极显著负相关,但与可育小穗数、百粒重、旗叶长和旗叶宽等农艺性状指标没有显著相关性。因此,通过导入抗病主效QTL可以显著改善感病材料的抗性,为进一步选育高产抗病品种提供基础材料。不良农艺性状的紧密连锁阻碍着抗赤霉病主效QTL的高效利用,需要通过继续回交或与其他品种杂交来打破这种遗传连锁关系。     

The introgression of chromosome 6P specifying for increased numbers of florets and kernels from Agropyron cristatum into wheat

A wheat (Triticum aestivum L.) line 4844 with superior numbers of florets and grains per spike was derived from the cross between Fukohokomugi wheat and Agropyron cristatum (L.) Gaertn. In order to determine the genetic control of floret and kernel number per spike in this line, chromosome addition and substitution lines that were derived from line 4844 were characterized by means of in situ hybridization, microsatellite (SSR), and gliadin analyses. Genomic in situ hybridization analysis with biotinylated P genomic DNA of A. cristatum as a probe demonstrated that the increased number of florets and grains in a spike was associated with the introgression of an A. cristatum chromosome. Fluorescence in situ hybridization, using a repetitive sequence, pAs1, derived from Aegilops squarrosa L., indicated the replacement of chromosome 6D of wheat in the wheat-A. cristatum chromosome substitution lines. This was confirmed by microsatellite analyses with wheat SSR markers specific for chromosome 6D, suggesting that the A. cristatum chromosome was homoeologous to group 6 and was therefore designated as 6P. This conclvsion was further confirmed by amplification using EST-SSR markers and gliadin analysis. The increased number of florets and kernels within a spike of the wheat-A. cristatum hybrids thus was controlled by gene(s) located on A. cristatum chromosome 6P.