Genetic dissection of yield-related traits in a recombinant inbred line population created using a key breeding parent in China’s wheat breeding

Understanding the genetics underlying yield formation of wheat is important for increasing wheat yield potential in breeding programs. Nanda2419 was a widely used cultivar for wheat production and breeding in China. In this study, we evaluated yield components and a few yield-related traits of a recombinant inbred line (RIL) population created by crossing Nanda2419 with the indigenous cultivar Wangshuibai in three to four trials at different geographical locations. Negative and positive correlations were found among some of these evaluated traits. Five traits had over 50 % trial-wide broad sense heritability. Using a framework marker map of the genome constructed with this population, quantitative trait loci (QTL) were identified for all traits, and epistatic loci were identified for seven of them. Our results confirmed some of the previously reported QTLs in wheat and identified several new ones, including QSn.nau-6D for effective tillers, QGn.nau-4B.2 for kernel number, QGw.nau-4D for kernel weight, QPh.nau-4B.2 and QPh.nau-4A for plant height, and QFlw.nau-5A.1 for flag leaf width. In the investigated population, Nanda2419 contributed all QTLs associated with higher kernel weight, higher leaf chlorophyll content, and a major QTL associated with wider flag leaf. Seven chromosome regions were related to more than one trait. Four QTL clusters contributed positively to breeding goal-based trait improvement through the Nanda2419 alleles and were detected in trials set in different ecological regions. The findings of this study are relevant to the molecular improvement of wheat yield and to the goal of screening cultivars for better breeding parents.     

Fine mapping Fhb4, a major QTL conditioning resistance to Fusarium infection in bread wheat (Triticum aestivum L.)

Qfhi.nau-4B is a major quantitative trait locus (QTL) against Fusarium graminearum infection identified in the Fusarium head blight-resistant germplasm Wangshuibai. To fine map this QTL, a recombinant inbred line (RIL) population of 530 lines derived from Nanda2419 × Wangshuibai and the BC₃F₂ population derived from the cross of a Qfhi.nau-4B near isogenic line (NIL) with susceptible cultivar Mianyang 99-323 as the recurrent parent were screened for recombinants occurred between microsatellite markers Xbarc20 and Xwmc349 that flank Qfhi.nau-4B. A total of 95 recombinants were obtained, including 45 RIL recombinants obtained through reverse-selection of Qfhi.nau-5A and 50 NIL recombinants from the BC₃F₂ population. Genotyping these recombinant lines with 22 markers mapping to the Xbarc20 and Xwmc349 interval revealed fourteen genotypes of the RIL recombinants as well as of the NIL recombinants. Two-year field evaluation of their resistance to Fusarium infection showed that these lines could be clearly classified into two groups according to percentage of infected spikes. The more resistant class had over 60% less infection than the susceptible class and were common to have Wangshuibai chromatin in the 1.7-cM interval flanked by Xhbg226 and Xgwm149. None of the susceptible recombinants had this Wangshuibai chromatin. Qfhi.nau-4B was thus confined between Xhbg226 and Xgwm149 and named Fhb4. The interval harboring Fhb4 was mapped to 4BL5-0.86–1.00 bin using Chinese Spring deletion lines, a region with about 5.7 times higher recombination rate than the genome average. This study established the basis for map-based cloning of Fhb4.     

Fine mapping TaFLW1, a major QTL controlling flag leaf width in bread wheat (Triticum aestivum L.)

Introduction

Flag leaf width (FLW) is directly related to photosynthetic capacity and yield potential in wheat. In a previous study, Qflw.nau-5A controlling FLW was detected on chromosome 5A in the interval possessing Fhb5 for type I Fusarium head blight (FHB) resistance using a recombinant inbred line population derived from Nanda2419 × Wangshuibai.

Materials and methods

Qflw.nau-5A near-isogenic line (NIL) with the background of Mianyang 99-323 and PH691 was developed and evaluated. FLW inheritance was investigated using two F₂ populations developed from crossing the Qflw.nau-5A NILs with their recurrent parents. One hundred ten and 28 recombinants, which included 10 and 5 types of recombinants, were identified from 2816 F₂ plants with Mianyang 99-323 background and 1277 F₂ plants with PH691 background, respectively, and phenotyped in field trials for FLW and type I FHB resistance. Deletion bin mapping was applied to physically map Qflw.nau-5A.

Results and conclusions

The introduction of Wangshuibai Qflw.nau-5A allele reduced the FLW up to 3 mm. In the F₂ populations, Qflw.nau-5A was inherited like a semi-dominant gene, and was therefore designated as TaFLW1. The FLW of the recombinant lines displayed a distinct two-peak distribution. Recombinants with wider leaves commonly have Mianyang 99-323 or PH691 chromatin in the 0.2 cM Xwmc492-Xwmc752 interval that resided in the 5AL12-0.35–0.57 deletion bin, and recombinants with narrow leaves were Wangshuibai genotype in this interval. Phenotypic recombination between FLW and type I FHB resistance was identified, implying TaFLW1 was in close linkage with Fhb5. These results should aid wheat breeders to break the linkage drag through marker-assisted selection and assist in the map-based cloning of TaFLW1.     

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.     

Precise mapping Fhb5, a major QTL conditioning resistance to Fusarium infection in bread wheat (Triticum aestivum L.)

Qfhi.nau-5A is a major quantitative trait locus (QTL) against Fusarium graminearum infection in the resistant wheat germplasm Wangshuibai. Genetic analysis using BC(3)F(2) and BC(4)F(2) populations, derived from selfing two near-isogenic lines (NIL) heterozygous at Qfhi.nau-5A that were developed, respectively, with Mianyang 99-323 and PH691 as the recurrent parent, showed that Qfhi.nau-5A inherited like a single dominant gene. This QTL was thus designated as Fhb5. To fine map it, these two backcross populations and a recombinant inbred line (RIL) population derived from Nanda2419?×?Wangshuibai were screened for recombinants occurring between its two flanking markers Xbarc56 and Xbarc100. Nineteen NIL recombinants were identified from the two backcross populations and nine from the RIL population. In the RIL recombinant selection process, selection against Fhb4 present in the RIL population was incorporated. Genotyping these recombinant lines with ten markers mapping to the Xbarc56-Xbarc100 interval revealed four types of Mianyang 99-323-derived NIL recombinants, three types of PH691-derived NIL recombinants, and four types of RIL recombinants. In different field trials, the percentage of infected spikes of these lines displayed a distinct two-peak distribution. The more resistant class had over 55% less infection than the susceptible class. Common to these resistant genotypes, the 0.3-cM interval flanked by Xgwm304 and Xgwm415 or one of these two loci was derived from Wangshuibai, while none of the susceptible recombinants had Wangshuibai chromatin in this interval. This interval harboring Fhb5 was mapped to the pericentromeric C-5AS3-0.75 bin through deletion bin mapping. The precise localization of Fhb5 will facilitate its utilization in marker-assisted wheat breeding programs.     

Marker-assisted development and evaluation of near-isogenic lines for scab resistance QTLs of wheat

Fusarium head blight or scab resistance in wheat is a complex quantitative trait affected greatly by environments. Therefore, the quantitative trait loci (QTL) for scab resistance found in mapping projects require validation to be effectively utilized in breeding programs. In this study, by employing both forward and background selections with the help of molecular markers, near-isogenic lines (NILs) for scab resistance QTLs Qfh.nau-2B, Qfhs.nau-3B, Qfhi.nau-4B and Qfhi.nau-5A, three of which originating in scab resistance germplasm Wangshuibai, were developed with the elite line Miangyang 99-323 as the recurrent parent. During the process of backcross, selection was based solely on marker genotypes of the target regions, and on recipient genome recovery rate in BC₂F₁ and BC₃F₁. All the identified BC₃F₁ plants with the target QTL regions have more than 94% recipient genome composition (RGC), and out of four to five of them a plant with over 97% RGC were obtained in each backcross combination. Compared with Mianyang 99-323, the Qfhs.nau-3B NIL showed much better resistance to disease spread within spikes, the Qfhi.nau-4B and Qfhi.nau-5A NILs showed much better resistance to initial infection, and the Qfh.nau-2B NIL showed improvement in both types of resistance. These results were consistent with findings in the previous QTL mapping studies. Morphologically and agronomically these NILs were similar to Mianyang 99-323 except that Qfhi.nau-4B NIL was taller and had a longer spike, and Qfhi.nau-5A NIL had narrower leaves. These results demonstrated the feasibility of marker-assisted utilization of scab resistance QTLs.     

Characterization and mapping of a Prbs gene controlling spike development in Hordeum vulgare L.

The barley mutant, poly-row-and-branched spike (prbs) showed altered inflorescence morphology: complete conversion of the rudimentary lateral spikelets in two-rowed barley into fully developed fertile spikelets similar to the six-rowed phenotype, and additional spikelets in the middle of spike. Moreover, branched spikes emerged in progeny from a cross between the mutant and a six-rowed barley cultivar. Morphological observation of the development of immature spikes of the mutant and descendants with branched spikes showed that the Prbs gene is involved in spikelet development in the triple-mound stage. In mutant prbs, new meristems initiated at the flanks of lateral spikelets and middle spikelet meristems were converted to branch meristems, developing branched spikes. These observations suggested that the Prbs gene plays a crucial role in spikelet initiation and identity maintenance. The Prbs gene may be an important modifier in inflorescence differentiation from a panicle into a spike. The branched spikes emerging in hybrids from a cross between the mutant and six-rowed barley cultivar were not conferred by the gene vrs1 or Int-c, which decide spike morphology in six-rowed barley. These results imply that although six-row genes vrs1 and Int-c and prbs have similar effects on lateral spikelet development, they have different functions in branched spikes. The Prbs gene was mapped to chromosome 3H between SSR marker Bmag0023 and marker Cbic60 at a genetic distance of 3.3 and 5.4 centimorgans (cM), respectively.     

Characterization of a common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) high-tillering dwarf mutant

Key message

A novel high-tillering dwarf mutant in common wheat Wangshuibai was characterized and mapped to facilitate breeding for plant height and tiller and the future cloning of the causal gene.

Abstract

Tiller number and plant height are two major agronomic traits in cereal crops affecting plant architecture and grain yield. NAUH167, a mutant of common wheat landrace Wangshuibai induced by ethylmethyl sulfide (EMS) treatment, exhibits higher tiller number and reduced plant height. Microscope observation showed that the dwarf phenotype was attributed to the decrease in the number of cells and their length. The same as the wild type, the mutant was sensitive to exogenous gibberellins. Genetic analysis showed that the high-tillering number and dwarf phenotype were related and controlled by a partial recessive gene. Using a RIL_2:6 population derived from the cross NAUH167/Sumai3, a molecular marker-based genetic map was constructed. The map consisted of 283 loci, spanning a total length of 1007.98 cM with an average markers interval of 3.56 cM. By composite interval mapping, a stable major QTL designated QHt.nau-2D controlling both traits, was mapped to the short arm of chromosome 2D flanked by markers Xcfd11 and Xgpw361. To further map the QHt.nau-2D loci, another population consisted of 180 F₂ progeny from a cross 2011I-78/NAUH167 was constructed. Finally, QHt.nau-2D was located within a genetic region of 0.8 cM between markers QHT239 and QHT187 covering a predicted physical distance of 6.77 Mb. This research laid the foundation for map-based cloning of QHt.nau-2D and would facilitate the characterization of plant height and tiller number in wheat.

     

Mapping QTLs of yield-related traits using RIL population derived from common wheat and Tibetan semi-wild wheat

Key message

QTLs controlling yield-related traits were mapped using a population derived from common wheat and Tibetan semi-wild wheat and they provided valuable information for using Tibetan semi-wild wheat in future wheat molecular breeding.

Abstract

Tibetan semi-wild wheat (Triticum aestivum ssp tibetanum Shao) is a kind of primitive hexaploid wheat and harbors several beneficial traits, such as tolerance to biotic and abiotic stresses. And as a wild relative of common wheat, heterosis of yield of the progeny between them was significant. This study focused on mapping QTLs controlling yield-related traits using a recombined inbred lines (RILs) population derived from a hybrid between a common wheat line NongDa3331 (ND3331) and the Tibetan semi-wild wheat accession Zang 1817. In nine location–year environments, a total of 148 putative QTLs controlling nine traits were detected, distributed on 19 chromosomes except for 1A and 2D. Single QTL explained the phenotypic variation ranging from 3.12 to 49.95 %. Of these QTLs, 56 were contributed by Zang 1817. Some stable QTLs contributed by Zang 1817 were also detected in more than four environments, such as QPh-3A1, QPh-4B1 and QPh-4D for plant height, QSl-7A1 for spike length, QEp-4B2 for ears per plant, QGws-4D for grain weight per spike, and QTgw-4D for thousand grain weight. Several QTL-rich Regions were also identified, especially on the homoeologous group 4. The TaANT gene involved in floral organ development was mapped on chromosome 4A between Xksm71 and Xcfd6 with 0.8 cM interval, and co-segregated with the QTLs controlling floret number per spikelet, explaining 4.96–11.84 % of the phenotypic variation. The current study broadens our understanding of the genetic characterization of Tibetan semi-wild wheat, which will enlarge the genetic diversity of yield-related traits in modern wheat breeding program.     

Branching Shoots and Spikes from Lateral Meristems in Bread Wheat

Wheat grain yield consists of three components: spikes per plant, grains per spike (i.e. head or ear), and grain weight; and the grains per spike can be dissected into two subcomponents: spikelets per spike and grains per spikelet. An increase in any of these components will directly contribute to grain yield. Wheat morphology biology tells that a wheat plant has no lateral meristem that forms any branching shoot or spike. In this study, we report two novel shoot and spike traits that were produced from lateral meristems in bread wheat. One is supernumerary shoot that was developed from an axillary bud at the axil of leaves on the elongated internodes of the main stem. The other is supernumerary spike that was generated from a spikelet meristem on a spike. In addition, supernumerary spikelets were generated on the same rachis node of the spike in the plant that had supernumerary shoot and spikes. All of these supernumerary shoots/spikes/spikelets found in the super wheat plants produced normal fertility and seeds, displaying huge yield potential in bread wheat.     

QTLs of cold tolerance-related traits at the booting stage for NIL-RILs in rice revealed by SSR

QTLs for cold tolerance-related traits at the booting stage using balanced population for 1525 recombinant inbred lines of near-isogenic lines (viz.NIL-RILs for BC5F3 and BC₅F₄ and BC₅F₅) over 3 years and two locations by backcrossing the strongly cold-tolerant landrace (Kunmingxiaobaigu) and a cold-sensitive cultivar (Towada) was analyzed. In this study, 676 microsatellite markers were employed to identify QTLs conferring cold tolerance at booting stage. Single marker analysis revealed that 12 markers associated with cold tolerance on chromosome 1, 4 and 5. Using a LOD significance threshold of 3.0,compositive interval mapping based on a mixed linear model revealed eight QTLs for 10 cold tolerance-related traits on chromosomes 1, 4, and 5. They were tentatively designatedqCTB-1-1, qCTB-4-1, qCTB-4-2, qCTB-4-3, qCTB-4-4, qCTB-4-5, qCTB-4-6, andqCTB-5-1. The marker intervals of them were narrowed to 0.3-6.8 cM. Genetic distances between the peaks of the QTL and nearest markers varied from 0 to 0.04 cM. We were noticed in some traits associated cold tolerance, such asqCTB-1-1 for 5 traits (plant height, panicle exsertion, spike length, blighted grains per spike and spikelet fertility),qCTB-4-1 for 8 traits (plant height, node length under spike, leaf length, leaf width, spike length, full grains per spike, total grains per spike and spikelet fertility),qCTB-4-2 for 3 traits (spike length, full grains per spike and spikelet fertility),qCTB-5-1 for 5 traits (plant height, panicle exsertion, blighted grains per spike, full grains per spike and spikelet fertility). The variance explained by a single QTL ranged from 0.80 to 16.80%. Three QTLs (qCTB-1-1, qCTB-4-1, qCTB-4-2) were detected in two or more trials. Our study sets a foundation for cloning cold-tolerance genes and provides opportunities to understand the mechanism of cold tolerance at the booting stage.     

Association and Validation of Yield-Favored Alleles in Chinese Cultivars of Common Wheat (Triticumaestivum L.)

Common wheat is one of the most important crops in China, which is the largest producer in the world. A set of 230 cultivars was used to identify yield-related loci by association mapping. This set was tested for seven yield-related traits, viz. plant height (PH), spike length (SL), spikelet number per spike (SNPS), kernel number per spike (KNPS), thousand-kernel weight (TKW), kernel weight per spike (KWPS), and sterile spikelet number (SSN) per plant in four environments. A total of 106 simple sequence repeat (SSR) markers distributed on all 21 chromosomes were used to screen the set. Twenty-one and 19 of them were associated with KNPS and TKW, respectively. Association mapping detected 73 significant associations across 50 SSRs, and the phenotypic variation explained (R²) by the associations ranged from 1.54 to 23.93%. The associated loci were distributed on all chromosomes except 4A, 7A, and 7D. Significant and potentially new alleles were present on 8 chromosomes, namely1A, 1D, 2A, 2D, 3D, 4B, 5B, and 6B. Further analysis showed that genetic effects of associated loci were greatly influenced by association panels, and the R² of crucial loci were lower in modern cultivars than in the mini core collection, probably caused by strong selection in wheat breeding. In order to confirm the results of association analysis, yield-related favorable alleles Xgwm135-1A₁₃₈, Xgwm337-1D₁₈₆, Xgwm102-2D₁₄₄, and Xgwm132-6B₁₂₈ were evaluated in a double haploid (DH) population derived from Hanxuan10 xLumai14.These favorable alleles that were validated in various populations might be valuable in breeding for high-yield.     

Mapping QTLs controlling kernel dimensions in a wheat inter-varietal RIL mapping population

Key message

Seven kernel dimension QTLs were identified in wheat, and kernel thickness was found to be the most important dimension for grain weight improvement.

Abstract

Kernel morphology and weight of wheat (Triticum aestivum L.) affect both yield and quality; however, the genetic basis of these traits and their interactions has not been fully understood. In this study, to investigate the genetic factors affecting kernel morphology and the association of kernel morphology traits with kernel weight, kernel length (KL), width (KW) and thickness (KT) were evaluated, together with hundred-grain weight (HGW), in a recombinant inbred line population derived from Nanda2419?×?Wangshuibai, with data from five trials (two different locations over 3 years). The results showed that HGW was more closely correlated with KT and KW than with KL. A whole genome scan revealed four QTLs for KL, one for KW and two for KT, distributed on five different chromosomes. Of them, QKl.nau-2D for KL, and QKt.nau-4B and QKt.nau-5A for KT were newly identified major QTLs for the respective traits, explaining up to 32.6 and 41.5% of the phenotypic variations, respectively. Increase of KW and KT and reduction of KL/KT and KW/KT ratios always resulted in significant higher grain weight. Lines combining the Nanda 2419 alleles of the 4B and 5A intervals had wider, thicker, rounder kernels and a 14% higher grain weight in the genotype-based analysis. A strong, negative linear relationship of the KW/KT ratio with grain weight was observed. It thus appears that kernel thickness is the most important kernel dimension factor in wheat improvement for higher yield. Mapping and marker identification of the kernel dimension-related QTLs definitely help realize the breeding goals.

     

Kernel weight per spike: what contributes to it at the individual QTL level?

Spike length (SL), spikelet number (SPN) per spike, kernel number per spike (KNPS), and thousand-kernel weight (TKW) have strong genetic associations with kernel weight per spike (KWPS) in wheat. To investigate their genetic relationships at the individual quantitative trait locus (QTL) level, both unconditional and conditional QTL mapping for KWPS with respect to SL, SPN, KNPS, and TKW were conducted. Two related F_8:9 recombinant inbred line populations, comprising 485 and 229 lines, respectively, were used. The trait phenotypic performances of each population were evaluated in four different environments. Unconditional QTL mapping analysis identified 22 putative additive QTL for KWPS, five of which were stable QTL, and only QKwps-WJ-1B.2 showed significant additive-by-environment interaction effects. In comparison with unconditional QTL mapping analysis, conditional QTL mapping analysis indicated that, at the QTL level, KNPS and TKW contributed more to KWPS than did SL and SPN. Any unconditional QTL for KWPS detected in this study was associated with at least one of its four related traits. The present study will provide assistance in the understanding of the genetic relationships between KWPS and its related traits.     

Interactions between SQUAMOSA and SHORT VEGETATIVE PHASE MADS-box proteins regulate meristem transitions during wheat spike development

Inflorescence architecture is an important determinant of crop productivity. The number of spikelets produced by the wheat inflorescence meristem (IM) before its transition to a terminal spikelet (TS) influences the maximum number of grains per spike. Wheat MADS-box genes VERNALIZATION 1 (VRN1) and FRUITFULL 2 (FUL2) (in the SQUAMOSA-clade) are essential to promote the transition from IM to TS and for spikelet development. Here we show that SQUAMOSA genes contribute to spikelet identity by repressing MADS-box genes VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), SHORT VEGETATIVE PHASE 1 (SVP1), and SVP3 in the SVP clade. Constitutive expression of VRT2 resulted in leafy glumes and lemmas, reversion of spikelets to spikes, and downregulation of MADS-box genes involved in floret development, whereas the vrt2 mutant reduced vegetative characteristics in spikelets of squamosa mutants. Interestingly, the vrt2 svp1 mutant showed similar phenotypes to squamosa mutants regarding heading time, plant height, and spikelets per spike, but it exhibited unusual axillary inflorescences in the elongating stem. We propose that SQUAMOSA–SVP interactions are important to promote heading, formation of the TS, and stem elongation during the early reproductive phase, and that downregulation of SVP genes is then necessary for normal spikelet and floral development. Manipulating SVP and SQUAMOSA genes can contribute to engineering spike architectures with improved productivity.

Functional characterization of developmental genes reveals ways to modify the wheat spike architecture to increase the number of grains and improve productivity.     

Molecular and comparative mapping of genes governing spike compactness from wild emmer wheat

The development and morphology of the wheat spike is important because the spike is where reproduction occurs and it holds the grains until harvest. Therefore, genes that influence spike morphology are of interest from both theoretical and practical stand points. When substituted for the native chromosome 2A in the tetraploid Langdon (LDN) durum wheat background, the Triticum turgidum ssp. dicoccoides chromosome 2A from accession IsraelA confers a short, compact spike with fewer spikelets per spike compared to LDN. Molecular mapping and quantitative trait loci (QTL) analysis of these traits in a homozygous recombinant population derived from LDN × the chromosome 2A substitution line (LDNIsA-2A) indicated that the number of spikelets per spike and spike length were controlled by linked, but different, loci on the long arm of 2A. A QTL explaining most of the variation for spike compactness coincided with the QTL for spike length. Comparative mapping indicated that the QTL for number of spikelets per spike overlapped with a previously mapped QTL for Fusarium head blight susceptibility. The genes governing spike length and compactness were not orthologous to either sog or C, genes known to confer compact spikes in diploid and hexaploid wheat, respectively. Mapping and sequence analysis indicated that the gene governing spike length and compactness derived from wild emmer could be an ortholog of the barley Cly1/Zeo gene, which research indicates is an AP2-like gene pleiotropically affecting cleistogamy, flowering time, and rachis internode length. This work provides researchers with knowledge of new genetic loci and associated markers that may be useful for manipulating spike morphology in durum wheat.     

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.

     

High-density mapping of the earliness per se-3Am (Eps-3A m ) locus in diploid einkorn wheat and its relation to the syntenic regions in rice and Brachypodium distachyon L.

In temperate grasses, such as wheat (Triticum sp.) and barley (Hordeum vulgare L.), earliness per se (eps) is defined as the intrinsic difference in flowering time of fully vernalized plants grown under long day conditions. The main task of our investigations was to confirm and refine the chromosomal position of the previously mapped Eps-3A ^m locus in einkorn wheat (Shindo et al. in Genome 45:563?C569, 2002; Hori et al. in Breed Sci 57:39?C45, 2007). To this end, 110 recombinant inbred lines (RILs) were phenotypically and genotypically evaluated. The population had been obtained from a cross between an early flowering X-ray mutant KT3-5 (T. monococcum L.) of cultivated spring type and a wild wheat line KT1-1 of T. boeoticum Boiss. (winter type). Heading time evaluations under greenhouse conditions resulted in a 10-day difference (P?=?0.008) between the mapping parents and a range of 49?days for the RIL population. Quantitative trait locus analyses of heading time, anthesis time, spikelet number and spike length showed the best linkage with marker loci close to the telomeric region of the long arm of chromosome 3A. The highest LOD values for heading time, anthesis time, spikelet number and spike length were 5.96, 5.40, 3.33 and 5.10, respectively (LOD threshold 2.0, P?<?0.05). Linkage analysis of 51 molecular markers delimited the new Eps-3A ^m interval to 0.9?cM, including 14 newly developed markers using collinearity with rice (Oryza sativa L.) and Brachypodium distachyon L. The present study marks a further step towards the molecular elucidation and functional analysis of Eps-3A ^m in wheat and other small grain cereals.     

Effect of decapitation on morphogenesis of stem and spike in various wheat species

Decapitation induced an additional formation of secondary shoots and anomalous spikes in all the species. The moan numbers of nodes, spikelets per spike, seeds per spikelet and spike, and the mean length of the stem and spike were reduced on secondary shoots of decapitated plants, while the mean and peak numbers of flowers per spikelet and the peak number of seeds per spikelet increased. The increase in the number of flowers per spikelet was the most striking on spike base; the seeds regularly occurred even in spikelets with an expressively increased number of flowers. The post-decapitation changes of the spike could be well expressed quantitatively according to the increased mean number of the flowers per one seed. Morphological ohanges in anomalous spikes of all the wheat species resemble phylogenetic reversions described in literature. Moreover, the peak numbers of flowers and seeds per spikelet were recorded in 52 varieties belonging to 21 wheat species. As compared with the decapitation trial, the greatest variability and the greatest differences between the speoies were also reoorded in the tetraploid group, and the smallest variability and differences between the species in the diploid group. We suppose that the striking morphological differences in post-decapitation spikes take place because the apical dominance was interrupted before differentiation of the recent form had been controlled in meristems on the decapitated stem base. Ancestral forms were morphologically realized with the help of an assimilating part of the decapitated stem.