Molecular characterization of field resistance to Fusarium head blight in two US soft red winter wheat cultivars

In the soft red winter wheat (Triticum aestivum L.) regions of the US, Fusarium head blight (FHB, caused by Fusarium spp.) resistance derived from locally adapted germplasm has been used predominantly. Two soft red winter wheat cultivars, Massey and Ernie, have moderate resistance to FHB. Mapping populations derived from Becker/Massey (B/M) and Ernie/MO 94-317 (E/MO) were evaluated for FHB resistance and other traits in multiple environments. Eight QTL in B/M and five QTL in E/MO were associated with FHB variables including incidence, severity (SEV), index (IND), Fusarium damaged kernels (FDK), deoxynivalenol (DON), and morphological traits flowering time and plant height. Four QTL were common to both populations. Three of them were located at or near known genes: Ppd-D1 on chromosome 2DS, Rht-B1 on 4BS, and Rht-D1 on 4DS. Alleles for dwarf plant height (Rht-B1b and Rht-D1b) and photoperiod insensitivity (Ppd-D1a) had pleiotropic effects in reducing height and increasing FHB susceptibility. The other QTL detected for FHB variables were on 3BL in both populations, 1AS, 1DS, 2BL, and 4DL in B/M, and 5AL (B1) and 6AL in E/MO. The additive effects of FHB variables ranged from 0.4 mg kg^?1 of DON to 6.2 % for greenhouse (GH) SEV in B/M and ranged from 0.3 mg kg^?1 of DON to 8.3 % for GH SEV in E/MO. The 4DS QTL had epistasis with Ppd-D1, Qdon.umc-6AL, and Qht.umc-4BS, and additive × additive × environment interactions with the 4BS QTL for SEV, IND, and FDK in E/MO. Marker-assisted selection might be used to enhance FHB resistance through selection of favorable alleles of significant QTL, taking into account genotypes at Rht-B1b, Rht-D1a and Ppd-D1a.     

Wild-type alleles of Rht-B1 and Rht-D1 as independent determinants of thousand-grain weight and kernel number per spike in wheat

The utilization of dwarfing genes Rht-B1b and Rht-D1b in wheat significantly increased grain yield and contributed to the “green revolution”. However, the benefit of Rht-B1b and Rht-D1b in drought environments has been debated. Although quantitative trait loci (QTL) for kernel number per spike (KN) and thousand-grain weight (TGW) have been found to be associated with Rht-B1 and Rht-D1, the confounding effect of environmental variation has made a direct association difficult to find. In this study, we used a doubled haploid population (225 lines) of Westonia × Kauz, in which both Rht-B1b (Kauz) and Rht-D1b (Westonia) segregated. The purpose of the study was to determine the interaction of Rht-B1 and Rht-D1 with grain yield components, namely KN and TGW, and to investigate genotype-by-environment interactions in glasshouse and field trials conducted in 2010 and 2011 in Western Australia. A genetic map of 1,156 loci was constructed using 195 microsatellite markers, two gene-based markers for Rht-B1 and Rht-D1, and 959 single nucleotide polymorphisms. The major QTL for TGW and KN were strongly linked to Rht-B1 and Rht-D1 loci and the positive effects were associated with the wild-type alleles, Rht-B1a and Rht-D1a. The major QTL of TGW were on chromosome 2D and 4B. The significant genetic effects (14.6–22.9 %) of TGW indicated that marker-assisted selection for TGW is possible, and markers gwm192a (206 bp) or gwm192b (236 bp) can be used as indicators of high TGW. For KN, one major QTL was detected on chromosome 4D in the analysis across three environments. The association of the wild-type alleles Rht-B1a and Rht-D1a in drought environments is discussed.     

Isolation of a gibberellin-insensitive dwarfing gene, Rht-B1e, and development of an allele-specific PCR marker

Gibberellins (GAs) are important phytohormones in plants. GAs promote plant growth by inducing the degradation of DELLA proteins, which serve as GA signal repressors. The semi-dwarfing genes Rht-B1b and Rht-D1b, derived from the Japanese variety Norin 10, are gain-of-function mutant alleles of the reduced height-1 genes (Rht-B1 and Rht-D1) encoding wheat DELLA proteins. Wheat varieties carrying these Rht alleles are shorter and insensitive to the GA response. At the Rht-B1 loci, an alternative GA-insensitive dwarfing gene, Rht-B1e, was found in the Russian mutant of Bezostaya1, or Krasznodari 1, by breeders, but its molecular mechanism for causing dwarfism remains unknown. In this study, the Rht-B1e allele was isolated using homology-based cloning. Sequence comparison between Rht-B1e and the wild-type Rht-B1a revealed an A-to-T substitution at nucleotide position 181 in Rht-B1e, which introduced a stop codon into the DELLA domain. Alignment of deduced amino acid sequences of Rht-B1e and Rht-B1b showed that the stop codon position in Rht-B1e was earlier than that of Rht-B1b by three amino acid residues, and it was also followed closely by several methionines, which may permit translational re-initiation, as seen in Rht-B1b. Yeast two-hybrid analysis revealed that the predicted Rht-B1e proteins did not interact with the GA receptor GID1 in the presence of GA, suggesting that the stop codon mutation in the DELLA domain is the molecular cause of GA insensitivity and dwarfism conferred by Rht-B1e in wheat. Meanwhile, we developed an allele-specific PCR marker for Rht-B1e, which may facilitate the use of the Rht-B1e dwarfing gene in wheat breeding programs.     

Control of late maturity alpha-amylase in wheat by the dwarfing gene Rht-D1b and genes on the 1B/1R translocation

The occurrence of late maturity alpha-amylase (LMA) was investigated using two doubled haploid wheat populations segregating for the dwarfing gene Rht-D1b and the 1B/1R translocation. Genotypes were assessed in the field and in controlled environments where a cold-shock treatment was used to induce LMA. Results from field-grown genotypes from the cross Spark × Rialto suggest that the absence of Rht-D1b or the presence of the 1B/1R translocation increases the expression of LMA.These two genetic factors were found to act independently and to have a positive interaction (complementary epistasis). In Option × Potent genotypes fixed for Rht-D1b, the 1B/1R effect was similar to that seen in the equivalent Spark × Rialto genotypes. Under controlled environment conditions, genotypes with the 1B/1R translocation showed a higher occurrence of LMA under both control and cold-shock conditions. 1B/1R was present in the majority of genotypes expressing LMA under control and cold-shock conditions. The results point to the novel finding that the 1B/1R translocation increases the expression of alpha-amylase in LMA-prone germplasm independently of effects of Rht-D1b, whereas previously it had been thought to act by a modification of the Rht-D1b effect.     

Identification and characterization of <Emphasis Type="Italic">Rht25</Emphasis>, a locus on chromosome arm 6AS affecting wheat plant height,heading time,and spike development

Key message

This study identified Rht25, a new plant height locus on wheat chromosome arm 6AS, and characterized its pleiotropic effects on important agronomic traits.

Abstract

Understanding genes regulating wheat plant height is important to optimize harvest index and maximize grain yield. In modern wheat varieties grown under high-input conditions, the gibberellin-insensitive semi-dwarfing alleles Rht-B1b and Rht-D1b have been used extensively to confer lodging tolerance and improve harvest index. However, negative pleiotropic effects of these alleles (e.g., poor seedling emergence and reduced biomass) can cause yield losses in hot and dry environments. As part of current efforts to diversify the dwarfing alleles used in wheat breeding, we identified a quantitative trait locus (QHt.ucw-6AS) affecting plant height in the proximal region of chromosome arm 6AS (<?0.4 cM from the centromere). Using a large segregating population (~?2800 gametes) and extensive progeny tests (70–93 plants per recombinant family), we mapped QHt.ucw-6AS as a Mendelian locus to a 0.2 cM interval (144.0–148.3 Mb, IWGSC Ref Seq v1.0) and show that it is different from Rht18. QHt.ucw-6AS is officially designated as Rht25, with Rht25a representing the height-increasing allele and Rht25b the dwarfing allele. The average dwarfing effect of Rht25b was found to be approximately half of the effect observed for Rht-B1b and Rht-D1b, and the effect is greater in the presence of the height-increasing Rht-B1a and Rht-D1a alleles than in the presence of the dwarfing alleles. Rht25b is gibberellin-sensitive and shows significant pleiotropic effects on coleoptile length, heading date, spike length, spikelet number, spikelet density, and grain weight. Rht25 represents a new alternative dwarfing locus that should be evaluated for its potential to improve wheat yield in different environments.

     

Gene-based high-density mapping of the gene rym7 conferring resistance to Barley mild mosaic virus (BaMMV)

For genetic analysis of Ppd-1 homoeologs controlling photoperiodic response of wheat (Triticum aestivum L.), bulk segregant analysis was performed using a doubled haploid (DH) population derived from a cross of Japanese wheat genotypes Winter-Abukumawase and Chihokukomugi. Based on the segregation of simple sequence repeat markers linked to the Ppd-1 homoeologs, Winter-Abukumawase carried insensitive alleles Ppd-B1a and Ppd-D1a and Chihokukomugi carried a single insensitive allele (Ppd-A1a) that was first found in common wheat. The genomic sequence of Ppd-1 homoeologs including the 5′ upstream region was determined and compared between the two genotypes. Ppd-D1a of Winter-Abukumawase had a deletion of 2,089 bp that was already reported for Ciano 67. Critical sequence polymorphism causing photoperiod insensitivity was not detected from the translation start codon to the 3′ untranslated region of Ppd-A1 and Ppd-B1. However, novel mutations were found in the 5′ upstream region. Ppd-A1a of Chihokukomugi had a deletion of 1,085 bp and Ppd-B1a of Winter-Abukumawase had an insertion of 308 bp. A total of 80 DH lines were classified into eight genotypes by PCR-based genotyping using specific primer sets to detect the In/Dels in the 5′ upstream region of three Ppd-1 genes. The heading dates of the DH lines differed significantly between the eight genotypes, showing that each of the three insensitive alleles accelerates heading by 7–9 days compared with the photoperiod-sensitive genotype. Interaction between the three genes was also significant.     

Genome-wide association study reveals genetic architecture of coleoptile length in wheat

Key message

Eight QTL for coleoptile length were identified in a genome-wide association study on a set of 893 wheat accessions, four of which are novel loci.

Abstract

Wheat cultivars with long coleoptiles are preferred in wheat-growing regions where deep planting is practiced. However, the wide use of gibberellic acid (GA)-insensitive dwarfing genes, Rht-B1b and Rht-D1b, makes it challenging to breed dwarf wheat cultivars with long coleoptiles. To understand the genetic basis of coleoptile length, we performed a genome-wide association study on a set of 893 landraces and historical cultivars using 5011 single nucleotide polymorphism (SNP) markers. Structure analysis revealed four subgroups in the association panel. Association analysis results suggested that Rht-B1b and Rht-D1b genes significantly reduced coleoptile length, and eight additional quantitative trait loci (QTL) for coleoptile length were also identified. These QTL explained 1.45–3.18 and 1.36–3.11% of the phenotypic variation in 2015 and 2016, respectively, and their allelic substitution effects ranged from 0.31 to 1.75 cm in 2015, and 0.63–1.55 cm in 2016. Of the eight QTL, QCL.stars-1BS1, QCL.stars-2DS1, QCL.stars-4BS2, and QCL.stars-5BL1 are likely novel loci for coleoptile length. The favorable alleles in each accession ranged from two to eight with an average of 5.8 at eight loci in the panel, and more favorable alleles were significantly associated with longer coleoptile, suggesting that QTL pyramiding is an effective approach to increase wheat coleoptile length.

     

<Emphasis Type="Italic">Rht24</Emphasis> reduces height in the winter wheat population ‘Solitär × Bussard’ without adverse effects on Fusarium head blight infection

Key message

The dwarfing gene Rht24 on chromosome 6A acts in the wheat population ‘Solitär × Bussard’, considerably reducing plant height without increasing Fusarium head blight severity and delaying heading stage.

Abstract

The introduction of the Reduced height (Rht)-B1 and Rht-D1 semi-dwarfing genes led to remarkable increases in wheat yields during the Green Revolution. However, their utilization also brings about some unwanted characteristics, including the increased susceptibility to Fusarium head blight. Thus, Rht loci that hold the potential to reduce plant height in wheat without concomitantly increasing Fusarium head blight (FHB) susceptibility are urgently required. The biparental population ‘Solitär × Bussard’ fixed for the Rht-1 wild-type alleles, but segregating for the recently described gibberellic acid (GA)-sensitive Rht24 gene, was analyzed to identify quantitative trait loci (QTL) for FHB severity, plant height, and heading date and to evaluate the effect of the Rht24 locus on these traits. The most prominent QTL was Rht24 on chromosome 6A explaining 51% of genotypic variation for plant height and exerting an additive effect of ? 4.80 cm. For FHB severity three QTL were detected, whereas five and six QTL were found for plant height and heading date, respectively. No FHB resistance QTL was co-localized with QTL for plant height. Unlike the Rht-1 semi-dwarfing alleles, Rht24b did not significantly affect FHB severity. This demonstrates that the choice of semi-dwarfing genes used in plant breeding programs is of utmost consideration where resistance to FHB is an important breeding target.

     

Genetic characterization and mapping of the Rht-1 homoeologs and flanking sequences in wheat

The introgression of Reduced height (Rht)-B1b and Rht-D1b into bread wheat (Triticum aestivum) varieties beginning in the 1960s led to improved lodging resistance and yield, providing a major contribution to the ‘green revolution’. Although wheat Rht-1 and surrounding sequence is available, the genetic composition of this region has not been examined in a homoeologous series. To determine this, three Rht-1-containing bacterial artificial chromosome (BAC) sequences derived from the A, B, and D genomes of the bread wheat variety Chinese Spring (CS) were fully assembled and analyzed. This revealed that Rht-1 and two upstream genes were highly conserved among the homoeologs. In contrast, transposable elements (TEs) were not conserved among homoeologs with the exception of intronic miniature inverted-repeat TEs (MITEs). In relation to the Triticum urartu ancestral line, CS-A genic sequences were highly conserved and several colinear TEs were present. Comparative analysis of the CS wheat BAC sequences with assembled Poaceae genomes showed gene synteny and amino acid sequences were well preserved. Further 5′ and 3′ of the wheat BAC sequences, a high degree of gene colinearity is present among the assembled Poaceae genomes. In the 20 kb of sequence flanking Rht-1, five conserved non-coding sequences (CNSs) were present among the CS wheat homoeologs and among all the Poaceae members examined. Rht-A1 was mapped to the long arm of chromosome 4 and three closely flanking genetic markers were identified. The tools developed herein will enable detailed studies of Rht-1 and linked genes that affect abiotic and biotic stress response in wheat.     

Allele frequencies in the VRN-A1, VRN-B1 and VRN-D1 vernalization response and PPD-B1 and PPD-D1 photoperiod sensitivity genes,and their effects on heading in a diverse set of wheat cultivars (Triticum aestivum L.)

Heading of cereals is determined by complex genetic and environmental factors in which genes responsible for vernalization and photoperiod sensitivity play a decisive role. Our aim was to use diagnostic molecular markers to determine the main allele types in VRN-A1, VRN-B1, VRN-D1, PPD-B1 and PPD-D1 in a worldwide wheat collection of 683 genotypes and to investigate the effect of these alleles on heading in the field. The dominant VRN-A1, VRN-B1 and VRN-D1 alleles were present at a low frequency. The PPD-D1a photoperiod-insensitive allele was carried by 57 % of the cultivars and was most frequent in Asian and European cultivars. The PPD-B1 photoperiod-insensitive allele was carried by 22 % of the genotypes from Asia, America and Europe. Nine versions of the PPD-B1-insensitive allele were identified based on gene copy number and intercopy structure. The allele compositions in PPD-D1, PPD-B1 and VRN-D1 significantly influenced heading and together explained 37.5 % of the phenotypic variance. The role of gene model increased to 39.1 % when PPD-B1 intercopy structure was taken into account instead of overall PPD-B1 type (sensitive vs. insensitive). As a single component, PPD-D1 had the most important role (28.0 % of the phenotypic variance), followed by PPD-B1 (12.3 % for PPD-B1_overall, and 15.1 % for PPD-B1_intercopy) and VRN-D1 (2.2 %). Significant gene interactions were identified between the marker alleles within PPD-B1 and between VRN-D1 and the two PPD1 genes. The earliest heading genotypes were those with the photoperiod-insensitive allele in PPD-D1 and PPD-B1, and with the spring allele for VRN-D1 and the winter alleles for VRN-A1 and VRN-B1. This combination could only be detected in genotypes from Southern Europe and Asia. Late-heading genotypes had the sensitivity alleles for both PPD1 genes, regardless of the allelic composition of the VRN1 genes. There was a 10-day difference in heading between the earliest and latest groups under field conditions.     

Resistance of bread wheat (Triticum aestivum L.) to preharvest sprouting: An association analysis

A statistical analysis of the data about 1422 bread wheat accessions with estimated preharvest sprouting was carried out. Close associations of preharvest sprouting resistance with the grain color and with resistance to Fusarium head blight were revealed, as well as weak, but statistically significant, associations with the habit, awnedness, and reduced height genes Rht-B1 and Rht-D1 (insensitive to gibberellin GA3). The pedigree analysis showed that the cluster structures of the gene pools of the North American red-grained and white-grained varieties are practically identical. In both groups, varieties that are resistant to preharvest sprouting differ from susceptible ones in the percentage of the contributions of the Crimean and Mediterranean landraces. Resistance is associated with a high contribution by the Crimean landrace and susceptibility is associated with a high contribution by the Mediterranean landrace.     

Earliness per se QTLs and their interaction with the photoperiod insensitive allele Ppd-D1a in the Cutler × AC Barrie spring wheat population

Earliness per se regulates flowering time independent of environmental signals and helps to fine tune the time of flowering and maturity. In this study, we aimed to map earliness per se quantitative trait loci (QTLs) affecting days to flowering and maturity in a population developed by crossing two spring wheat cultivars, Cutler and AC Barrie. The population of 177 recombinant inbred lines (RILs) was genotyped for a total of 488 SSR and DArT polymorphic markers on all 21 chromosomes. Three QTLs of earliness per se affecting days to flowering and maturity were mapped on chromosomes 1B (QEps.dms-1B1 and QEps.dms-1B2) and 5B (QEps.dms-5B1), in individual environments and when all the environments were combined. A QTL affecting flowering time (QFlt.dms-4A1) was identified on chromosome 4A. Two grain yield QTLs were mapped on chromosome 5B, while one QTL was mapped on chromosome 1D. The population segregated for the photoperiod insensitive gene, Ppd-D1a, and it induced earlier flowering by 0.69 days and maturity by 1.28 days. The photoperiod insensitive allele Ppd-D1a interacted in an additive fashion with QTLs for flowering and maturity times. The earliness per se QTL QFlt.dms-5B.1 inducing earlier flowering could help to elongate grain filling duration for higher grain yield. Hence, chromosome 5B possesses promising genomic regions that may be introgressed for higher grain yield with earlier maturity through marker-assisted selection in bread wheat.     

Efficacy of pyramiding elite alleles for dynamic development of plant height in common wheat

Plant height is an important botanical feature closely related to yield. Two populations consisting of 118 and 262 accessions respectively were used to identify elite alleles for plant height and to validate their allelic effects. Plant height was measured from the early booting to the flowering stages. Simple sequence repeat markers for candidate quantitative trait locus (QTL) regions with large effects identified in a doubled haploid (DH) population (Hanxuan 10 × Lumai 14) were selected for further verification by association analysis. Nine loci significantly (P < 0.001) associated with plant height were detected 13 times in the population with 118 accessions. Three loci (Xgwm11-1B, Xwmc349-4B and Xcfd23-4D) were identified in three, two and two periods of plant height growth, respectively. Markers Xbarc168-2D, Xgwm249-2D, Xwmc349-4B, Xcfd23-4D and Xgwm410-5A located at or near additive QTL regions in the DH population proved to coincide with known Rht loci. The results showed a consistency between linkage analysis and association mapping, and also confirmed the value of fine mapping of QTL through combined linkage and association analyses. For final plant height, the alleles Xgwm11-1B ₂₀₈ , Xwmc349-4B ₁₀₃ and Xcfd23-4D ₂₀₂ exhibited negative effects, i.e. reducing plant height; Xwmc349-4B ₁₀₁ and Xcfd23-4D ₂₀₅ showed significant positive effects. A second larger population (262 accessions) was used to validate the effects of these large-effect alleles and the efficacy of pyramiding in eight environments (year × site × water regime combinations). Strong correlations between final plant height and numbers of large-effect alleles indicated that the alleles contributed additively to plant height. The additive effects showed that pyramiding elite alleles for target traits has significant potential for wheat breeding.     

Contrasting effects of dwarfing alleles and nitrogen availability on mineral concentrations in wheat grain

Background and aim

Concentrations of essential minerals in plant foods may have declined in modern high-yielding cultivars grown with large applications of nitrogen fertilizer (N). We investigated the effect of dwarfing alleles and N rate on mineral concentrations in wheat.

Methods

Gibberellin (GA)-insensitive reduced height (Rht) alleles were compared in near isogenic wheat lines. Two field experiments comprised factorial combinations of wheat variety backgrounds, alleles at the Rht-B1 locus (rht-B1a, Rht-B1b, Rht-B1c), and different N rates. A glasshouse experiment also included Rht-D1b and Rht-B1b+D1b in one background.

Results

In the field, depending on season, Rht-B1b increased crop biomass, dry matter (DM) harvest index, grain yield, and the economically-optimal N rate (N _opt ). Rht-B1b did not increase uptake of Cu, Fe, Mg or Zn so these minerals were diluted in grain. Nitrogen increased DM yield and mineral uptake so grain concentrations were increased (Fe in both seasons; Cu, Mg and Zn in one season). Rht-B1b reduced mineral concentrations at N _opt in the most N responsive season. In the glasshouse experiment, grain yield was reduced, and mineral concentrations increased, with Rht allele addition.

Conclusion

Effects of Rht alleles on Fe, Zn, Cu and Mg concentrations in wheat grain are mostly due to their effects on DM, rather than of GA-insensitivity on N _opt or mineral uptake. Increased N requirement in semi-dwarf varieties partly offsets this dilution effect.     

The effect of day-neutral mutations in barley and wheat on the interaction between photoperiod and vernalization

Vernalization-2 (Vrn-2) is the major flowering repressor in temperate cereals. It is only expressed under long days in wild-type plants. We used two day-neutral (photoperiod insensitive) mutations that allow rapid flowering in short or long days to investigate the day length control of Vrn-2. The barley (Hordeum vulgare) early maturity8 (eam8) mutation affects the barley ELF3 gene. eam8 mutants disrupt the circadian clock resulting in elevated expression of Ppd-H1 and the floral activator HvFT1 under short or long days. When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2. We also investigated the wheat (Triticum aestivum) Ppd-D1a mutation. This differs from eam8 in causing elevated levels of Ppd-1 and TaFT1 expression without affecting the circadian clock. We used genotypes that differed in “short-day vernalization”. Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation. The latter showed Vrn-2 expression in short days. In summary, eam8 and Ppd-D1a mimic long days in terms of photoperiod response, causing Vrn-2 to become aberrantly expressed (in short days). As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.     

Genome-wide association study of heading and flowering dates and construction of its prediction equation in Chinese common wheat

Heading date is one of the most important traits in wheat breeding as it affects adaptation and yield potential. A genome-wide association study (GWAS) using the 90 K iSelect SNP genotyping assay indicated that a total of 306 loci were significantly associated with heading and flowering dates in 13 environments in Chinese common wheat from the Yellow and Huai wheat region. Of these, 105 loci were significantly correlated with both heading and flowering dates and were found in clusters on chromosomes 2, 5, 6, and 7. Based on differences in distribution of the vernalization and photoperiod genes among chromosomes, arms, or block regions, 13 novel, environmentally stable genetic loci were associated with heading and flowering dates, including RAC875_c41145_189 on 1DS, RAC875_c50422_299 on 2BL, and RAC875_c48703_148 on 2DS, that accounted for more than 20% phenotypic variance explained (PVE) of the heading/flowering date in at least four environments. GWAS and t test of a combination of SNPs and vernalization and photoperiod alleles indicated that the Vrn-B1, Vrn-D1, and Ppd-D1 genes significantly affect heading and flowering dates in Chinese common wheat. Based on the association of heading and flowering dates with the vernalization and photoperiod alleles at seven loci and three significant SNPs, optimal linear regression equations were established, which show that of the seven loci, the Ppd-D1 gene plays the most important role in modulating heading and flowering dates in Chinese wheat, followed by Vrn-B1 and Vrn-D1. Additionally, three novel genetic loci (RAC875_c41145_189, Excalibur_c60164_137, and RAC875_c50422_299) also show important effect on heading and flowering dates. Therefore, Ppd-D1, Vrn-B1, Vrn-D1, and the novel genetic loci should be further investigated in terms of improving heading and flowering dates in Chinese wheat. Further quantitative analysis of an F₁₀ recombinant inbred lines population identified a major QTL that controls heading and flowering dates within the Ppd-D1 locus with PVEs of 28.4% and 34.0%, respectively; this QTL was also significantly associated with spike length, peduncle length, fertile spikelets number, cold resistance, and tiller number.     

Responses to booster hepatitis B vaccination are significantly correlated with genotypes of human leukocyte antigen (HLA)-DPB1 in neonatally vaccinated adolescents

Genome-wide association studies have identified single nucleotide polymorphisms (SNPs) near the human leukocyte antigen (HLA)-DP loci that were significantly correlated with outcomes of hepatitis B virus (HBV) infection. We performed a case–control study nested in a well-characterized cohort of booster recipients to assess whether genetic variants of HLA-DPB1 are also associated with response to hepatitis B (HB) vaccination. The cases and controls were 171 and 510 booster recipients whose post-booster titers of antibodies against HBV surface antigen (anti-HBs) were undetectable and detectable, respectively. The HLA-DPB1 genotype was determined using sequence-based techniques. The frequencies of HLA-DPB1 alleles were significantly different between cases and controls (p = 1.7 × 10^?8). The HLA-DPB1 05:01 and 09:01 alleles were significantly more frequent in the cases, and 02:01:02, 02:02, 03:01:01, 04:01:01, and 14:01, were significantly more frequent in the controls. The adjusted odds ratio (OR) of undetectable post-booster anti-HBs titers was significantly correlated with the number of risk alleles (p for trend = 3.8 × 10^?5). For the number of protective alleles, the trend was significantly inversed (p for trend = 1.3 × 10^?5). As compared with subjects with two risk alleles, adjusted OR were 0.34 (95 % confidence interval [CI] 0.21–0.55) and 0.20 (95 % CI 0.08–0.48) for subjects with 1 and 2 protective alleles, respectively. The HLA-DPB1 02:02, 04:01:01, 05:01 and 09:01 alleles were also significantly correlated with the likelihoods of undetectable pre-booster anti-HBs titers. Our results indicated that HLA-DPB1 is significantly correlated with response to booster HB vaccination in adolescent who had received postnatal active HB vaccination. HLA-DBP1 may also determine the long-term persistence of response to HB vaccination.     

Cloning and characterization of <Emphasis Type="Italic">Tabas1</Emphasis>-<Emphasis Type="Italic">B1</Emphasis> gene associated with flag leaf chlorophyll content and thousand-grain weight and development of a gene-specific marker in wheat

The chloroplast photosystem of flag leaves contributes the largest proportion of photosynthates to grain in crops and consequently affects grain weight. The plant 2-Cys peroxiredoxin BAS1 is involved in chlorophyll protection against chloroplast damage. In the present study, we cloned a Tabas1 gene in common wheat (Triticum aestivum L.), comprising seven exons and six introns with a complete sequence of 2847 bp and an open reading frame of 789 bp. The gene was located on chromosome 2B, and designated Tabas1-B1. A codominant gene-specific marker TaS1 was developed based on a 1-bp InDel (-/A) in the second intron of Tabas1-B1. Two alleles, Tabas1-B1a and Tabas1-B1b, at the Tabas1-B1 locus were identified by TaS1. Linkage and quantitative trait locus (QTL) mapping indicated that Tabas1-B1 was linked to Xcfa2278 (5.23 cM) and Xbarc167 (10.38 cM) on chromosome 2BL. A stable QTL co-segregating with Tabas1-B1 explained 9.0–19.2 % of phenotypic variations for chlorophyll content (ChlC) and 9.5–15.5 % for thousand-grain weight (TGW), respectively, across three environments. Association analysis further indicated a significant and positive effect of Tabas1-B1a on the ChlC of flag leaf post-anthesis and TGW in two populations across four environments. Geographic distribution analysis suggested a slightly higher frequency of Tabas1-B1a than Tabas1-B1b in the main wheat-growing regions of China. Selection of Tabas1-B1a may increase grain weight in wheat breeding.     

Exploiting the <Emphasis Type="Italic">Rht</Emphasis> portfolio for hybrid wheat breeding

Key message

The portfolio of available Reduced height loci (Rht-B1, Rht-D1, and Rht24) can be exploited for hybrid wheat breeding to achieve the desired heights in the female and male parents, as well as in the hybrids, without adverse effects on other traits relevant for hybrid seed production.

Abstract

Plant height is an important trait in wheat line breeding, but is of even greater importance in hybrid wheat breeding. Here, the height of the female and male parental lines must be controlled and adjusted relative to each other to maximize hybrid seed production. In addition, the height of the resulting hybrids must be fine-tuned to meet the specific requirements of the farmers in the target regions. Moreover, this must be achieved without adversely impacting traits relevant for hybrid seed production. In this study, we explored Reduced height (Rht) loci effective in elite wheat and exploited their utilization for hybrid wheat breeding. We performed association mapping in a panel of 1705 wheat hybrids and their 225 parental lines, which besides the Rht-B1 and Rht-D1 loci revealed Rht24 as a major QTL for plant height. Furthermore, we found that the Rht-1 loci also reduce anther extrusion and thus cross-pollination ability, whereas Rht24 appeared to have no adverse effect on this trait. Our results suggest different haplotypes of the three Rht loci to be used in the female or male pool of a hybrid breeding program, but also show that in general, plant height is a quantitative trait controlled by numerous small-effect QTL. Consequently, marker-assisted selection for the major Rht loci must be complemented by phenotypic selection to achieve the desired height in the female and male parents as well as in the wheat hybrids.