Association mapping of dynamic developmental plant height in common wheat

Drought as a major abiotic stress often occurs from stem elongation to the grain filling stage of wheat in northern China. Plant height (PH) is a suitable trait to model the dissection of drought tolerance. The purposes of the present study were to validate molecular markers for PH developmental behavior and identify elite alleles of molecular markers. After the phenotyping of 154 accessions for PH dynamic development under well-watered (WW) and drought stressed (DS) conditions, and the genotyping of 60 SSR markers from six candidate chromosome regions related to PH found in our previous linkage mapping studies, both parameters PH and drought tolerance coefficient (DTC) calculated by the conditional analysis were used for association mapping. A total of 46 significant association signals (P < 0.01) were identified in 23 markers, and phenotypic variation ranged from 7 to 50%. Among them, four markers Xgwm261-2D, Xgwm495-4B, Xbarc109-4B and Xcfd23-4D were detected under both water regimes. Furthermore, 10 markers were associated with DTC, and four with both parameters PH and DTC at the same plant development stage. The results revealed different allelic effects of associated markers; for example, the 155 bp Xgwm495-4B allele was associated with a reduced height of −11.2 cm under DS and −15.3 cm under WW, whereas the 167 bp allele exhibited increased height effects of 3.9 and 8.1 cm, respectively. This study demonstrates a strong power of joint association analysis and linkage mapping for the identification of important genes in wheat.     

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.     

Association of microsatellite loci alleles of the group-5 of chromosomes and the frost resistance of winter wheat

Determination of the frost resistance and a microsatellite analysis of the group 5 chromosomes were performed on parental varieties and recombinant inbred lines F ₇ Luzanovka odesskaya/Odesskaya krasnokolosaya. The allelic differences of the Xcfd7-5B, Xwmc415-5B, and Xgwm182-5D microsatellite loci were associated with the level of frost resistance of the lines.     

Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 × Wangshuibai population. II: Type I resistance

Fusarium head blight (FHB) is a serious disease in wheat and barley affecting both yield and quality. To identify genes for resistance to infection, the RIL population derived from ‘Nanda2419’ × ‘Wangshuibai’ and the parents were evaluated for percentage of infected spikes (PIS) in four different environments. Using a 2,960 cM marker framework map constructed for this population, ten chromosome regions were detected for their association with type I resistance through interval mapping with Mapmaker/QTL, among which QTLs mapped in the intervals of Xwmc349~Xgwm149 on chromosome 4B, of Xwmc96~Xgwm304 on chromosome 5A and of Xgwm408~Xbarc140 on chromosome 5B were revealed in at least three environments and have Wangshuibai as the source of resistance alleles. Qfhi.nau-4B and Qfhi.nau-5A had larger effects and explained up to 17.5 and 27.0% of the phenotypic variance, respectively. To detect epistasis QTLs, two-locus interactions were examined by whole genome scan. Interactions of five locus pairs were found to have significant effects on type I resistance with the LOD score ranging 3.8–6.5 and four of them conferred resistance in parental phase. The one with the most significant effect was Xcfd42~Xgwm469 (6D)/Xwmc390-2~Xbd04 (2A) pair. No QTL × E interaction was detected for PIS. It was found that flowering time did not have significant effects on PIS in this population. Our studies indicated that Wangshuibai is useful for breeding for both type I and type II scab resistance and the markers associated with the QTLs could be used in marker-assisted selection and isolation of scab-resistance QTLs. F. Lin and S.L. Xue equally contributed to this article     

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.     

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.     

Identification and validation of SSR markers linked to the stem rust resistance gene Sr6 on the short arm of chromosome 2D in wheat

The wheat stem rust resistance gene Sr6, present in several wheat cultivars, confers a high level of resistance against a wide range of races of Puccinia graminis f. sp. tritici. Resistance conferred by Sr6 is influenced by temperature, light intensity, and genetic background of the recipient genotype. Here, we report the identification and validation of molecular markers linked to Sr6 that can be used for the detection of this gene in wheat breeding programs. A mapping population of 136 F₂ plants and their F_2:3 families derived from a cross between near-isogenic lines, ‘Chinese Spring’ and ISr6-Ra, were screened for stem rust reaction in the seedling stage. Bulked segregant analysis (BSA) based on seedling tests was used to screen 418 SSR markers that covered the entire genome of wheat. Four markers, Xwmc453, Xcfd43, Xcfd77, and Xgwm484, were mapped within a chromosome region that spanned 9.7 cM from Sr6. The closest markers, Xwmc453 and Xcfd43, were linked to Sr6 at a distance of 1.1 and 1.5 cM, respectively. The markers Xwmc453 and Xcfd43 amplified Sr6-specific marker alleles that were diagnostic for Sr6 in a diverse set of 46 wheat accessions and breeding lines developed and/or collected in Australia, Canada, China, Egypt, Ethiopia, Kenya, Mexico, South Africa, and USA. These markers can now be used for marker-assisted selection of Sr6 and for pyramiding it with other stem rust resistance genes.     

Molecular markers for tracking variation in lipoxygenase activity in wheat breeding

Lipoxygenase (LOX) activity is an important factor determining the color of flour and end-use products of wheat. In the present study, quantitative trait loci (QTL) for LOX activity in common wheat were mapped using 71 doubled haploid (DH) lines derived from a Zhongyou 9507 × CA9632 cross, and SSR markers. Two QTL, QLpx.caas.1AL and QLpx.caas-4B, were identified on chromosomes 1AL and 4B, closely associated with LOX activity. The SSR loci Xwmc312 and Xgwm251 proved to be diagnostic and explained 13.4–25.2% of the phenotypic variance for the 1AL locus and 14.3–27.0% for the 4B locus across four environments. The SSR markers Xgwm251 and Xwmc312 were validated across 198 Chinese wheat cultivars and advanced lines and showed highly significant (P < 0.01) association with LOX activity. We further established a multiplexed PCR with SSR marker combination Xwmc312/Xgwm251 to test these wheat cultivars and advanced lines. The results suggested that the marker combination Xwmc312/Xgwm251 is efficient and reliable for evaluating LOX activity and can be used in marker-assisted selection (MAS) for targeting flour color attributes to noodle and other wheat-based products.     

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.

     

Rht-1 and Ppd-D1 associations with height, GA sensitivity, and days to heading in a worldwide bread wheat collection

Reduced height (Rht)-1 and Photoperiod (Ppd) have major effects on the adaptability of bread wheat (Triticum aestivum) to specific environments. Ppd–D1a is a photoperiod insensitive allele that reduces time to flowering. The gibberellin (GA) insensitive alleles Rht–B1b and Rht–D1b shorten plant stature and were important components of the ‘green revolution’. Two additional Rht–B1 alleles were recently identified that contain a 160 or 197 bp insertion upstream of the coding region and may affect plant height or GA sensitivity Wilhelm et al. (Theor Appl Gen doi:10.1007/s00122-013-2088-7, 2013b). We determined the frequency of the five alleles in a worldwide core collection of 372 wheat accessions (372CC) and estimated their effects on height, days to heading, and GA sensitivity when the collection was grown in pots outdoors or in the glasshouse. This revealed that each allele was widespread geographically with frequencies ranging from 0.12 to 0.25. Ppd-D1a was associated with significant (p ≤ 0.05) reductions in days to heading and height relative to photoperiod sensitive Ppd-D1b. Relative to wild type, Rht-B1b and Rht-D1b each resulted in significant reductions in height (approximately 30 %) and GA sensitivity. The 160 and 197 bp alleles were associated with significant height reductions of 18 and 12 %, respectively, and with non-significant reductions in GA sensitivity relative to wild type. Two statistical methods were developed and used to estimate GA sensitivity of the 372CC accessions, but novel GA insensitive alleles were not identified. Further characterization of the Rht-B1 insertion alleles is required, but our results suggest these may enable fine adjustments in plant height.     

Fine mapping of the region on wheat chromosome 7D controlling grain weight

We report the fine mapping of the previously described quantitative trait loci (QTL) for grain weight QTgw.ipk-7D associated with microsatellite marker Xgwm1002-7D by using introgression lines (ILs) carrying introgressions of the synthetic wheat W-7984 in the genetic background of the German winter wheat variety ‘Prinz’. The BC₄F₃ ILs had a 10% increased thousand grain weight compared to the control group and the recurrent parent ‘Prinz’, and 84.7% of the phenotypic variance could be explained by the segregation of marker Xgwm1002-7D, suggesting the presence of a gene modulating grain weight, which was preliminarily designated gw1. It was possible to delimit the QTL QTgw.ipk-7D to the interval Xgwm295–Xgwm1002, which is located in the most telomeric bin 7DS4-0.61-1.00 in the physical map of wheat chromosome arm 7DS. Furthermore, our data suggest the presence of a novel plant height-reducing locus Rht on chromosome arm 7DS of ‘Prinz’. Larger grain and increased plant height may reflect the pleiotropic action of one gene or may be caused by two linked genes. In general, our data support the concept of using nearly isogenic ILs for validating and dissecting QTLs into single Mendelian genes and open the gateway for map-based cloning of a grain-weight QTL in wheat.     

Chromosomal location of genomic SSR markers associated with yellow rust resistance in Turkish bread wheat (Triticum aestivum L.)

We have previously reported Xgwm382 as a diagnostic marker for disease resistance against yellow rust in Izgi2001 × ES14 F₂ population. Among the same earlier tested 230 primers, one SSR marker (Xgwm311) also amplified a fragment which is present in the resistant parent and in the resistant bulks, but absent in the susceptible parent and in the susceptible bulks. To understand the chromosome group location of these diagnostic markers, Xgwm382 and Xgwm311, in the same population, we selected 16 SSR markers mapped only in one genome of chromosome group 2 around 1–21 cM distance to these diagnostic markers based on the SSR consensus map of wheat. Out of 16 SSRs, Xwmc658 identified resistant F₂ individuals as a diagnostic marker for yellow rust disease and provided the location of Xgwm382 and Xgwm311 on chromosome 2AL in our plant material.     

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.     

Mapping QTLs for physiological and biochemical traits related to grain yield under control and terminal heat stress conditions in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

In order to detect genomic regions with different effects for some of the physiological and biochemical traits of wheat, four experiments were conducted at Research Farm of Agricultural and Natural Resources Research Center of Zabol in 2015–2016 and 2016–2017 growing seasons. The experiments were carried out using four alpha lattice designs with two replications under non-stress and terminal heat stress conditions. Plant materials used in this study included 167 recombinant inbred lines and their parents (‘SeriM82’ and ‘Babax’). Six traits including grain yield (GY), proline content (PRO), water soluble carbohydrates (WSC), maximum efficiency of photosystem II (Fv/Fm), cytoplasmic membrane stability (CMS) and chlorophyll content (CHL) were evaluated. Genetic linkage map consisted of 211 AFLP marker, 120 SSR marker and 144 DArT markers with 1864 cm length and 4.4 cm mean distance. QTL analysis was carried out using a mixed-model-based composite interval mapping (MCIM) method. By the combined analysis of normal phenotypic values, 27 additive QTLs and five pairs of epistatic effects were identified for studied traits, among which two additive and one epistatic QTL showed significant QTL?×?environment interactions. By the combined analysis of stress phenotypic values, a total of 26 QTLs with additive effects and 5 epistatic QTLs were detected, among which one additive and one epistatic QTL showed QTL?×?environment interactions. Six QTLs with major effects (QGY-2B, QGY-2D, QPro-5B, QWSC-4A, QFv/Fm-6A and QCMS-4B), which were common between two conditions could be useful for marker-assisted selection (MAS) in order to develop heat tolerant and high-performance wheat varieties.     

Molecular mapping of a powdery mildew resistance gene in common wheat landrace Baihulu and its allelism with Pm24

Powdery mildew is one of the most devastating diseases of wheat in areas with cool and maritime climates. Chinese wheat landrace Baihulu confers a high level of resistance against a wide range of Blumeria graminis DC f. sp. tritici (Bgt) races, especially those currently prevailing in Shaanxi. The objectives of this study were to determine the chromosome bin location of the mlbhl gene from Baihulu and its allelism with Pm24. To investigate the inheritance of powdery mildew resistance and detect adjacent molecular markers, we constructed a segregating population of 301 F₂ plants and corresponding F_2:3 families derived from Baihulu/Shaanyou 225. Genetic analysis revealed that a single dominant gene was responsible for seedling stage powdery mildew resistance in Baihulu. A genetic map comprising Xgwm106, Xgwm337, Xgwm1675, Xgwm603, Xgwm789, Xbarc229, Xgpw4503, Xcfd72, Xcfd83, Xcfd59, Xcfd19, and mlbhl spanned 28.2?cM on chromosome 1D. Xgwm603/Xgwm789 and Xbarc229 were flanking markers tightly linked to mlbhl at genetic distances of 1.5 and 1.0?cM, respectively. The mlbhl locus was located in chromosome bin 1DS 0.59–1.00 delimited by the SSR markers Xgwm337 and Xbarc229. When tested with a differential array of 23 Bgt isolates Baihulu displayed a response pattern that was clearly distinguishable from that of Chiyacao and varieties or lines possessing documented Pm genes. Allelism analysis indicated that mlbhl is a new gene, either allelic or closely linked with Pm24. The new gene was designated Pm24b.     

Lycopene-ε-cyclase (e-LCY3A) is functionally associated with quantitative trait loci for flour b* colour on chromosome 3A in wheat (Triticum aestivum L.)

Flour b* colour is an important grain quality parameter for specific wheat end-products. The genetic control of b* colour in Australian wheat accessions is controlled by quantitative trait loci (QTL) on chromosomes 3A, 3B, 7A and 7B accumulating lutein, a compound of the carotenoid biosynthetic pathway. The relationship between lutein accumulation and flour b* colour provides an opportunity to identify sequence variants of genes encoding enzymes from the biosynthetic pathway that may control trait variation. This study identified a single nucleotide polymorphism (SNP) in the gene encoding lycopene-ε-cylcase on chromosome 3A (e-LYC3A) between two wheat accessions Ajana and WAWHT2074, identifying two alleles, e-LYC3Aa and e-LYC3Ab, respectively. e-LCY3Ab was present in 62.5 % of the wheat accessions analysed. A highly significant (P < 0.01) association with QTL on chromosome 3A in two mapping populations indicated that e-LYC3A is functionally associated with b* colour variation in some Australian wheat accessions. The SNP induced a serine/glycine substitution at amino acid residue 123 and a subtle change in protein folding at amino acid residue 119. The e-LYC3A SNP may be considered along with other alleles and genes on homoeologous group 3 and 7 chromosomes for selecting desirable flour b* colour variation in marker-assisted breeding.     

Inheritance and mapping of powdery mildew resistance gene <Emphasis Type="Italic">Pm43</Emphasis> introgressed from <Emphasis Type="Italic">Thinopyrum</Emphasis><Emphasis Type="Italic">intermedium</Emphasis> into wheat

Powdery mildew resistance from Thinopyrum intermedium was introgressed into common wheat (Triticum aestivum L.). Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from powdery mildew resistant line CH5025 revealed that resistance was controlled by a single dominant allele. The gene responsible for powdery mildew resistance was mapped by the linkage analysis of a segregating F₂ population. The resistance gene was linked to five co-dominant genomic SSR markers (Xcfd233, Xwmc41, Xbarc11, Xgwm539 and Xwmc175) and their most likely order was Xcfd233–Xwmc41–Pm43–Xbarc11–Xgwm539–Xwmc175 at 2.6, 2.3, 4.2, 3.5 and 7.0 cM, respectively. Using the Chinese Spring nullisomic-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome 2DL. As no powdery mildew resistance gene was previously assigned to chromosome 2DL, this new resistance gene was designated Pm43. Pm43, together with the identified closely linked markers, could be useful in marker-assisted selection for pyramiding powdery mildew resistance genes. Runli He and Zhijian Chang contributed equally to this work.     

<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.

     

Brassinosteroid leaf unrolling QTL mapping in durum wheat

Brassinosteroids are a newly reported class of plant growth phytohormones found in plants throughout the plant kingdom. Functioning at very low concentrations, they play an essential role in improving biomass yield and stress tolerance. There are no reports in the literature of the genetic variability of responsiveness of brassinosteroids in wheat; most studies on brassinosteroids have focused on the physiological effects of exogenous addition of brassinosteroids. Our aim was to study the genetic variation in the responsiveness of a doubled haploid durum wheat population to three brassinosteroid concentrations using the leaf unrolling test, which is a simple bioassay to test brassinosteroid activity. An F₁-derived doubled haploid population of 77 individuals from the cross Strongfield/Blackbird was used to construct a genetic map of 427 molecular marker loci. The leaf unrolling test was performed on the parents and doubled haploid genotypes of the population using 0.2, 2 and 20 nM brassinosteroid concentrations. The results indicated significant differences in leaf unrolling between the two parents, doubled haploid genotypes, treatments and genotype-by-treatment combinations. Transgressive segregation beyond Strongfield of leaf unrolling was observed for all concentrations, with the strongest response at 20 nM. Putative quantitative trait loci were revealed in the intervals Xgwm2–Xbarc45 on chromosome 3A and Xwmc643a–Xwmc625a on chromosome 3B. Additional quantitative trait loci were associated with markers Xwmc48a, Xwmc511, Xwmc89a and Xgwmc692 on chromosome 4B, and Xwmc17 on chromosome 7A. This work should enhance the understanding of the relationship between stress tolerance and productivity, and responsiveness to brassinosteroids.