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Key message: A likely new locus QSns.sau-MC-3D.1 associated with SNS showing no negative effect on yield-related traits compared to WAPO1 was identified and validated in various genetic populations under multiple environments. The number of spikelets per spike (SNS) is one of the crucial factors determining wheat yield. Thus, improving our understanding of the genes that regulate SNS could help develop wheat varieties with higher yield. In this study, a recombinant inbred line (RIL) population (MC) containing 198 lines derived from a cross between msf and Chuannong 16 (CN16) was used to construct a genetic linkage map using the GenoBaits Wheat 16 K Panel. The genetic map contained 5,991 polymorphic SNP markers spanning 2,813.25 cM. A total of twelve QTL for SNS were detected, and two of them, i.e., QSns.sau-MC-3D.1 and QSns.sau-MC-7A, were stably expressed. QSns.sau-MC-3D.1 had high LOD values ranging from 4.99 to 11.06 and explained 9.71–16.75% of the phenotypic variation. Comparison of QSns.sau-MC-3D.1 with previously reported SNS QTL suggested that it is likely a novel one, and two kompetitive allele-specific PCR (KASP) markers were further developed. The positive effect of QSns.sau-MC-3D.1 was also validated in three biparental populations and a diverse panel containing 388 Chinese wheat accessions. Genetic analysis indicated that WHEAT ORTHOLOG OFAPO1 (WAPO1) was a candidate gene for QSns.sau-MC-7A. Pyramiding of QSns.sau-MC-3D.1 and WAP01 had a great additive effect increasing SNS by 7.10%. Correlation analysis suggested that QSns.sau-MC-3D.1 was likely independent of effective tiller number, plant height, spike length, anthesis date, and thousand kernel weight. However, the H2 haplotype of WAPO1 may affect effective tiller number and plant height. These results indicated that utilization of QSns.sau-MC-3D.1 should be given priority for wheat breeding. Geographical distribution analysis showed that the positive allele of QSns.nsau-MC-3D.1 was dominant in most wheat-producing regions of China, and it has been positively selected among modern cultivars released in China since the 1940s. Gene prediction, qRT-PCR analysis, and sequence alignment suggested that TraesCS3D03G0216800 may be the candidate gene of QSns.nsau-MC-3D.1. Taken together, these results enrich our understanding of the genetic basis of wheat SNS and will be useful for fine mapping and cloning of the gene underlying QSns.sau-MC-3D.1. [ABSTRACT FROM AUTHOR]

Key message: A co-located KL and TKW-related QTL with no negative effect on PH and AD was rapidly identified using BSA and wheat 660 K SNP array. Its effect was validated in a panel of 218 wheat accessions. Kernel length (KL) and thousand-kernel weight (TKW) of wheat (Triticum aestivum L.) contribute significantly to kernel yield. In the present study, a recombinant inbred line (RIL) population derived from the cross between the wheat line S849-8 with larger kernels and more spikelets per spike and the line SY95-71 was developed. Further, of both the bulked segregant analysis (BSA) and the wheat 660 K single nucleotide polymorphism (SNP) array were used to rapidly identify genomic regions for kernel-related traits from this RIL population. Kompetitive Allele Specific PCR markers were further developed in the SNP-enriched region on the 2D chromosome to construct a genetic map. Both QKL.sicau-SSY-2D for KL and QTKW.sicau-SSY-2D for TKW were identified at multiple environments on chromosome arm 2DL. These two QTLs explained 9.68–23.02% and 6.73–18.32% of the phenotypic variation, respectively. The effects of this co-located QTL were successfully verified in a natural population consisting of 218 Sichuan wheat accessions. Interestingly, the major QTL was significantly and positively correlated with spike length, but did not negatively affect spikelet number per spike (SNS), plant height, or anthesis date. These results indicated that it is possible to synchronously improve kernel weight and SNS by using this QTL. Additionally, several genes associated with kernel development and filling rate were predicted and sequenced in the QTL-containing physical intervals of reference genomes of 'Chinese spring' and Aegilops tauschii. Collectively, these results provide a QTL with great breeding potential and its linked markers which should be helpful for fine mapping and molecular breeding. [ABSTRACT FROM AUTHOR]

Key message: A novel light intensity-dependent lesion mimic mutant with enhanced disease resistance was physiologically, biochemically, and genetically characterized, and the causative gene was fine mapped to a 1.28 Mbp interval containing 17 high-confidence genes. Lesion mimic mutants are ideal for studying disease resistance and programmed cell death photosynthesis in plants to improve crop yield. In this study, a novel light intensity-dependent lesion mimic mutant (MC21) was obtained from the wheat variety Chuannong16 (CN16) by ethyl methane sulfonate treatment. The mutant initially developed tiny lesion spots on the basal part of the leaves, which then gradually proceeded down to leaf sheaths, stems, shells, and awns at the flowering stage. The major agronomic traits were significantly altered in the mutant compared to that in the wild-type CN16. Furthermore, the mutant exhibited a lesion phenotype with degenerated chloroplast structure, decreased chlorophyll content, increased level of reactive oxygen species, and increased resistance to stripe rust and powdery mildew. Genetic analysis indicated that the lesion phenotype was controlled by a novel single semi-dominant nuclear gene. The target gene was mapped on chromosome arm 2AL located between Kompetitive Allele Specific PCR (KASP) markers, KASP-4211 and KASP-5353, and tentatively termed as lesion mimic 5 (Lm5). The fine mapping suggested that Lm5 was located in a 1.28 Mbp interval between markers KASP-5825 and KASP-9366; 17 high-confidence candidate genes were included in this genomic region. This study provides an important foundational step for further cloning of Lm5 using a map-based approach. [ABSTRACT FROM AUTHOR]

The Chinese wheat landrace "Gaoxianguangtoumai" (GX) has exhibited a high level of adult-plant resistance (APR) to stripe rust in the field for more than a decade. To reveal the genetic background for APR to stripe rust in GX, a set of 249 F6:8 (F6, F7, and F8) recombinant inbred lines (RILs) was developed from a cross between GX and the susceptible cultivar "Taichung 29." The parents and RILs were evaluated for disease severity at the adult-plant stage in the field by artificial inoculation with the currently predominant Chinese Puccinia striiformis f. sp. tritici races during three cropping seasons and genotyped using the Wheat 55K single-nucleotide polymorphism (SNP) array to construct a genetic map with 1,871 SNP markers finally. Two stable APR quantitative trait loci (QTL), QYr.GX-2AS and QYr.GX-7DS in GX, were detected on chromosomes 2AS and 7DS, which explained 15.5–27.0% and 11.5–13.5% of the total phenotypic variation, respectively. Compared with published Yr genes and QTL, QYr.GX-7DS and Yr18 may be the same, whereas QYr.GX-2AS is likely to be novel. Haplotype analysis revealed that QYr.GX-2AS is likely to be rare which presents in 5.3% of the 325 surveyed Chinese wheat landraces. By analyzing a heterogeneous inbred family (HIF) population from a residual heterozygous plant in an F8 generation of RIL, QYr.GX-2AS was further flanked by KP2A_36.85 and KP2A_38.22 with a physical distance of about 1.37Mb and co-segregated with the KP2A_37.09. Furthermore, three tightly linked Kompetitive allele-specific PCR (KASP) markers were highly polymorphic among 109 Chinese wheat cultivars. The results of this study can be used in wheat breeding for improving resistance to stripe rust. [ABSTRACT FROM AUTHOR]

Kernel size (KS) and kernel weight play a key role in wheat yield. Phenotypic data from six environments and a Wheat55K single-nucleotide polymorphism array–based constructed genetic linkage map from a recombinant inbred line population derived from the cross between the wheat line 20828 and the line SY95-71 were used to identify quantitative trait locus (QTL) for kernel length (KL), kernel width (KW), kernel thickness (KT), thousand-kernel weight (TKW), kernel length–width ratio (LWR), KS, and factor form density (FFD). The results showed that 65 QTLs associated with kernel traits were detected, of which the major QTLs QKL.sicau-2SY-1B , QKW.sicau-2SY-6D , QKT.sicau-2SY-2D , and QTKW.sicau-2SY-2D , QLWR.sicau-2SY-6D , QKS.sicau-2SY-1B / 2D / 6D , and QFFD.sicau-2SY-2D controlling KL, KW, KT, TKW, LWR, KS, and FFD, and identified in multiple environments, respectively. They were located on chromosomes 1BL, 2DL, and 6DS and formed three QTL clusters. Comparison of genetic and physical interval suggested that only QKL.sicau-2SY-1B located on chromosome 1BL was likely a novel QTL. A Kompetitive Allele Specific Polymerase chain reaction (KASP) marker, KASP-AX-109379070 , closely linked to this novel QTL was developed and used to successfully confirm its effect in two different genetic populations and three variety panels consisting of 272 Chinese wheat landraces, 300 Chinese wheat cultivars most from the Yellow and Huai River Valley wheat region, and 165 Sichuan wheat cultivars. The relationships between kernel traits and other agronomic traits were detected and discussed. A few predicted genes involved in regulation of kernel growth and development were identified in the intervals of these identified major QTL. Taken together, these stable and major QTLs provide valuable information for understanding the genetic composition of kernel yield and provide the basis for molecular marker–assisted breeding. [ABSTRACT FROM AUTHOR]

Key message: A novel, stably expressed, and plant height-independent QTL for spike extension length on 5AS was identified and validated in different populations using a newly developed and tightly linked KASP marker. As an important component of plant height (PH), spike extension length (SEL) plays a significant role in formation of an ideotype in wheat. Despite the fact that numerous loci for SEL in wheat have been reported, our knowledge on PH-independent loci remains to be limited. In this study, two recombinant inbred line (RIL) populations genotyped using the Wheat55K SNP were used to detect quantitative trait loci (QTL) controlling SEL across six environments. A total of 30 QTL for SEL were detected in these two RIL populations, and four of them, i.e., QSEL.sicau-2CN-4D, QSEL.sicau-2SY-4B.2, QSEL.sicau-2SY-4D.1, and QSEL.sicau-2CN-5A, were stably expressed. Genetic and conditional QTL analysis showed that the first three were significantly associated with PH, while the last one, QSEL.sicau-2CN-5A, is independent of PH. Comparison of genetic and physical maps suggested that only QSEL.sicau-2CN-5A located on chromosome arm 5AS is likely a novel QTL. A Kompetitive Allele-Specific PCR (KASP) marker, KASP-AX-110413733, tightly linked to this novel QTL was developed to successfully confirm its effect in three different genetic populations. Further, in the interval where QSEL.sicau-2CN-5A was located on 'Chinese Spring' wheat reference genome, three promising genes mainly expressed in wheat stem were predicated and they all encode the cytochrome P450 that was demonstrated to be closely associated with SEL elongation in rice. In addition, significant correlations between SEL and PH, spikelet number per spike, and thousand-grain weight were also detected. Altogether, our results broaden our understanding on genetic basis of SEL and will be useful for marker-based selection of lines with different SELs and fine mapping the novel and PH-independent QTL QSEL.sicau-2CN-5A. [ABSTRACT FROM AUTHOR]

Spike density (SD), an important spike morphological trait associated with wheat yield, is the spikelet number per spike (SNS) divided by spike length (SL). In this study, phenotypic data from eight environments were collected and a recombinant inbred line population (RIL) constructed by the wheat line 20828 and the cultivar 'Chuannong16' and a Wheat55K SNP array‐based constructed genetic linkage map were used to identify SD quantitative trait locus (QTL). Correlation between SD and other agronomic traits was calculated. Genes associated with plant growth and development for major loci were predicted. The results showed that 24 QTLs associated with SD were detected in eight environments. Among them, three major QTL, namely QSd.sicau‐5B.2, QSd.sicau‐2D.3 and QSd.sicau‐4B.1, explained up to 35.62%, 14.21% and 11.23% of phenotypic variation, respectively. The positive alleles of them were all derived from 'Chuannong16'. The significant relationships between SD and other agronomic traits were detected and discussed. Taken together, the stably expressed SD QTL under different environments identified in this study provided theoretical guidance for further fine mapping and germplasm improvement. [ABSTRACT FROM AUTHOR]

Key message: Major and environmentally stable QTL for flag leaf-related traits in wheat were identified and validated across ten environments using six populations with different genetic backgrounds. Flag leaf size and posture are two important factors of "ideotype" in wheat. Despite numerous studies on genetic analysis of flag leaf size including flag leaf length (FLL), width (FLW), area (FLA) and the ratio of length/width (FLR), few have focused on flag leaf posture including flag leaf angle (FLANG), opening angle (FLOA) and bend angle (FLBA). Further, the numbers of major, environmentally stable and verified genetic loci for flag leaf-related traits are limited. In this study, QTL for FLL, FLW, FLA, FLR, FLANG, FLOA and FLBA were identified based on a recombinant inbred line population together with values from up to ten different environments. Totally, eight major and stably expressed QTL were identified. Three co-located chromosomal intervals for seven major QTL were identified. The five major QTL QFll.sicau-5B.3 and QFll.sicau-2D.3 for FLL, QFlr.sicau-5B for FLR, QFlw.sicau-2D for FLW and QFla.sicau-2D for FLA were successfully validated by the tightly linked Kompetitive Allele Specific PCR (KASP) markers in the other five populations with different genetic backgrounds. A few genes related to leaf growth and development in intervals for these major QTL were predicated. Significant relationships between flag leaf- and yield-related traits were evidenced by analyses of Pearson correlations, conditional QTL and genetic mapping. Taken together, these results provide valuable information for understanding flag leaf size and posture of "ideotype" as well as fine mapping and breeding utilization of promising loci in bread wheat. [ABSTRACT FROM AUTHOR]

Key message: A major and stably expressed QTL for spikelet number per spike identified in a 2-cM interval on chromosome arm 2DS was validated using two populations with different genetic backgrounds. Spikelet number per spike (SNS) plays a key role in wheat yield improvement. Numerous genetic and environmental factors influencing SNS have been documented, but the number of major, stably expressed and validated loci underlying SNS is still limited. In this study, a recombinant inbred line (RIL) population derived from a normal spikelet cultivar and a multiple-spikelet wheat line (with a longer spike with more canonically oriented apical spikelets) was genotyped using a Wheat55K single-nucleotide polymorphism (SNP) array and simple sequence repeat (SSR) markers. SNS was measured for this RIL population in eight environments. Five QTL were each identified in two or more environments. One of them, QSns.sau-2D (LOD = 3.47–38.24, PVE = 10.16–45.68%), was detected in all the eight environments. The QTL was located in a 2-cM interval on chromosome arm 2DS flanked by the markers AX-109836946 and AX-111956072. This QTL, QSns.sau-2D, significantly increased SNS by up to 14.72%. Several genes associated with plant growth and development were identified in the physical interval of QSns.sau-2D. This QTL was further validated by the tightly linked Kompetitive Allele Specific PCR (KASP) marker, KASP-AX-94721936, in two other populations with different genetic backgrounds. The significant correlation between SNS and anthesis date, plant height, spike length, grain number per spike and thousand-grain weight were detected and discussed. These results lay the foundation for fine mapping and cloning gene(s) underlying QSns.sau-2D. [ABSTRACT FROM AUTHOR]

Stripe rust (or yellow rust), caused by the fungus Puccinia striiformis f. sp. tritici ( Pst), is one of the most important foliar diseases of wheat. Characterization and utilization of novel resistant genes is the most effective, economic and environmentally friendly approach to controlling the disease. Wheat line LM168-1, which was derived from a cross between common wheat Chuannong 16 and Milan, has good adult-plant resistance to stripe rust, based on field tests over several years. To elucidate the genetic basis of resistance, LM168-1 was crossed with susceptible variety SY95-71. Parents and F1, F2, BC1 and F2:3 progenies were tested in 2009-2011 in a field inoculated with the predominant races of Pst in China. The genetic analysis showed that resistance to stripe rust in LM168-1 was controlled by a single recessive gene, temporarily designated yrLM168. Simple sequence repeat (SSR), resistance gene analog polymorphism (RGAP) and target region amplification polymorphism (TRAP) techniques were used to identify molecular markers linked to the resistance locus. Finally, a linkage group consisting of two SSR, four RGAP and five TRAP markers was constructed for yrLM168 with 102 F2 plants. The closest markers R1 and R2 flanked the resistance gene locus at 2.4 and 2.4 cM, respectively. Furthermore, two SSR markers Xwmc59 and Xwmc145 assigned the gene to chromosome 6A. Because yrLM168 confers high-level resistance to the predominant races of Pst in China, it should be useful in stripe rust resistance breeding programs. The closely linked markers can be used for rapidly transferring yrLM168 to wheat breeding populations. [ABSTRACT FROM AUTHOR]

Background: Kernel length (KL), kernel width (KW) and thousand-kernel weight (TKW) are key agronomic traits in wheat breeding. Chuannong16 ('CN16') is a commercial cultivar with significantly longer kernels than the line '20828'. To identify and characterize potential alleles from CN16 controlling KL, the previously developed recombinant inbred line (RIL) population derived from the cross '20828' × 'CN16' and the genetic map constructed by the Wheat55K SNP array and SSR markers were used to perform quantitative trait locus/loci (QTL) analyses for kernel traits. Results: A total of 11 putative QTL associated with kernel traits were identified and they were located on chromosomes 1A (2 QTL), 2B (2 QTL), 2D (3 QTL), 3D, 4A, 6A, and 7A, respectively. Among them, three major QTL, QKL.sicau-2D, QKW.sicau-2D and QTKW.sicau-2D, controlling KL, KW and TKW, respectively, were detected in three different environments. Respectively, they explained 10.88–18.85%, 17.21–21.49% and 10.01–23.20% of the phenotypic variance. Further, they were genetically mapped in the same interval on chromosome 2DS. A previously developed kompetitive allele-specific PCR (KASP) marker KASP-AX-94721936 was integrated in the genetic map and QTL re-mapping finally located the three major QTL in a 1- cM region flanked by AX-111096297 and KASP-AX-94721936. Another two co-located QTL intervals for KL and TKW were also identified. A few predicted genes involved in regulation of kernel growth and development were identified in the intervals of these identified QTL. Significant relationships between kernel traits and spikelet number per spike and anthesis date were detected and discussed. Conclusions: Three major and stably expressed QTL associated with KL, KW, and TKW were identified. A KASP marker tightly linked to these three major QTL was integrated. These findings provide information for subsequent fine mapping and cloning the three co-localized major QTL for kernel traits. [ABSTRACT FROM AUTHOR]

• Chinese wheat landraces were assessed for stripe rust resistance at the seedling stage and the adult-plant stage. • Performed a genome-wide association study to ASR and APR stripe rust using DArT markers. • Identified ten potential novel ASR and APR loci for wheat stripe rust. Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is one of the most devastating foliar diseases in wheat. Host resistance is the most effective strategy for the management of the disease. To screen for accessions with stable resistance and identify effective stripe rust resistance loci, a genome-wide association study (GWAS) was conducted using a panel of 140 Chinese wheat landraces. The panel was evaluated for stripe rust response at the adult-plant stage at six field-year environments with mixed races and at the seedling stage with two separate predominant races of the pathogen, and genotyped with the genome-wide Diversity Arrays Technology markers. The panel displayed abundant phenotypic variation in stripe rust responses, with 9 landraces showing stable resistance to the mixture of Pst races at the adult-plant stage in the field and 10 landraces showing resistance to individual races at the seedling stage in the greenhouse. GWAS identified 12 quantitative trait loci (QTL) significantly (P ≤ 0.001) associated to stripe rust resistance using the field data of at least two environments and 18 QTL using the seedling data with two races. Among these QTL, 10 were presumably novel, including 4 for adult-plant resistance mapped to chromosomes 1B (QYrcl.sicau-1B.3), 4A (QYrcl.sicau-4A.3), 6A (QYrcl.sicau-6A.2) and 7B (QYrcl.sicau-7B.2) and 6 for all-stage resistance mapped to chromosomes 2D (QYrcl.sicau-2D.1), 3B (QYrcl.sicau-3B.3), 3D (QYrcl.sicau-3D), 4B (QYrcl.sicau-4B), 6A (QYrcl.sicau-6A.1) and 6D (QYrcl.sicau-6D). The landraces with stable resistance can be used for developing wheat cultivars with effective resistance to stripe rust. [ABSTRACT FROM AUTHOR]