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Key Message: A major and stable QTL for sterile florets per spike and sterile florets per spikelet was identified, it was mapped within a 2.22-Mb interval on chromosome 5AL, and the locus was validated using two segregating populations with different genetic backgrounds. Both the number of fertile florets per spike (FFS) and the number of sterile florets per spike (SFS) significantly influence the final yield of wheat (Triticum aestivum L.), and a trade-off theoretically exists between them. To enhance crop yield, wheat breeders have historically concentrated on easily measurable traits such as FFS, spikelets per spike, and spike length. Other traits of agronomic importance, including SFS and sterile florets per spikelet (SFPs), have been largely overlooked. In the study, reported here, genetic bases of SFS and SFPs were investigated based on the assessment of a population of recombinant inbred lines (RILs) population. The RIL population was developed by crossing a spontaneous mutant with higher SFS (msf) with the cultivar Chuannong 16. A total of 10 quantitative trait loci (QTL) were identified, with QSFS.sau-MC-5A for SFS and QSFPs.sau-MC-5A for SFPs being the major and stable ones, and they were co-located on the long arm of chromosome 5A. The locus was located within a 2.22-Mb interval, and it was further validated in two additional populations based on a tightly linked Kompetitive Allele-Specific PCR (KASP) marker, K_sau_5A_691403852. Expression differences and promoter sequence variations were observed between the parents for both TraesCS5A03G1247300 and TraesCS5A03G1250300. The locus of QSFS.sau-MC-5A/QSFPs.sau-MC-5A showed a significantly positive correlation with spike length, florets in the middle spikelet, and total florets per spike, but it showed no correlation with either kernel number per spike (KNS) or kernel weight per spike. Appropriate nitrogen fertilizer application led to reduced SFS and increased KNS, supporting results from previous reports on the positive effect of nitrogen fertilizer on wheat spike and floret development. Based on these results, we propose a promising approach for breeding wheat cultivars with multiple fertile florets per spike, which could increase the number of kernels per spike and potentially improve yield. Collectively, these findings will facilitate further fine mapping of QSFS.sau-MC-5A/QSFPs.sau-MC-5A and be instrumental in strategies to increase KNS, thereby enhancing wheat yield., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Key Message: A co-located novel QTL for TFS, FPs, FMs, FFS, FFPs, KWS, and KWPs with potential of improving wheat yield was identified and validated. Spike-related traits, including fertile florets per spike (FFS), kernel weight per spike (KWS), total florets per spike (TFS), florets per spikelet (FPs), florets in the middle spikelet (FMs), fertile florets per spikelet (FFPs), and kernel weight per spikelet (KWPs), are key traits in improving wheat yield. In the present study, quantitative trait loci (QTL) for these traits evaluated under various environments were detected in a recombinant inbred line population (msf/Chuannong 16) mainly genotyped using the 16 K SNP array. Ultimately, we identified 60 QTL, but only QFFS.sau-MC-1A for FFS was a major and stably expressed QTL. It was located on chromosome arm 1AS, where loci for TFS, FPs, FMs, FFS, FFPs, KWS, and KWPs were also simultaneously co-mapped. The effect of QFFS.sau-MC-1A was further validated in three independent segregating populations using a Kompetitive Allele-Specific PCR marker. For the co-located QTL, QFFS.sau-MC-1A, the presence of a positive allele from msf was associate with increases for all traits: + 12.29% TFS, + 10.15% FPs, + 13.97% FMs, + 17.12% FFS, + 14.75% FFPs, + 22.17% KWS, and + 19.42% KWPs. Furthermore, pleiotropy analysis showed that the positive allele at QFFS.sau-MC-1A simultaneously increased the spike length, spikelet number per spike, and thousand-kernel weight. QFFS.sau-MC-1A represents a novel QTL for marker-assisted selection with the potential for improving wheat yield. Four genes, TraesCS1A03G0012700, TraesCS1A03G0015700, TraesCS1A03G0016000, and TraesCS1A03G0016300, which may affect spike development, were predicted in the physical interval harboring QFFS.sau-MC-1A. Our results will help in further fine mapping QFFS.sau-MC-1A and be useful for improving wheat yield., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Key Message: A novel and stably expressed QTL QSNS.sicau-SSY-7A for spikelet number per spike in wheat without negative effects on thousand-kernel weight was identified and validated in different genetic backgrounds. Spikelet number per spike (SNS) is an important determinant of yield in wheat. In the present study, we combined bulked segregant analysis (BSA) and the wheat 660 K single-nucleotide polymorphism (SNP) array to rapidly identify genomic regions associated with SNS from a recombinant inbred line (RIL) population derived from a cross between the wheat lines S849-8 and SY95-71. A genetic map was constructed using Kompetitive Allele Specific PCR markers in the SNP-enriched region on the long arm of chromosome 7A. A major and stably expressed QTL, QSNS.sicau-SSY-7A, was detected in multiple environments. It was located in a 1.6 cM interval on chromosome arm 7AL flanked by the markers AX-109983514 and AX-109820548. This QTL explained 6.86-15.72% of the phenotypic variance, with LOD values ranging from 3.66 to 8.66. Several genes associated with plant growth and development were identified in the interval where QSNS.sicau-SSY-7A was located on the 'Chinese Spring' wheat and wild emmer reference genomes. Furthermore, the effects of QSNS.sicau-SSY-7A and WHEAT ORTHOLOG OFAPO1(WAPO1) on SNS were analyzed. Interestingly, QSNS.sicau-SSY-7A significantly increased SNS without negative effects on thousand-kernel weight, anthesis date and plant height, demonstrating its great potential for breeding aimed at improving grain yield. Taken together, these results indicate that QSNS.sicau-SSY-7A is a promising locus for yield improvement, and its linkage markers are helpful for fine mapping and molecular breeding., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Key Message: Two major and stably expressed QTL for traits related to mature wheat embryo independent of kernel size were identified and validated in a natural population that contained 171 Sichuan wheat accessions and 49 Sichuan wheat landraces. As the juvenile of a highly differentiated plant, mature wheat (Triticum aestivum L.) embryos are highly significant to agricultural production. To understand the genetic basis of traits related to wheat embryo size, the embryo of mature kernels in a recombination inbred line that contained 126 lines from four environments was measured. The genetic loci of embryo size, including embryo length (EL), embryo width (EW), embryo area (EA), embryo length/kernel length (EL/KL), embryo width/kernel width (EW/KW), and EL/EW, were identified based on a genetic linkage map constructed based on PCR markers and the Wheat 55 K single nucleotide polymorphism (SNP) array. A total of 50 quantitative trait loci (QTL) for traits related to wheat embryo size were detected. Among them, QEL.sicau-2SY-4A for EL and QEW.sicau-2SY-7B for EW were major and stably expressed and were genetically independent of KL and KW, respectively. Their effects were further verified in a natural population that contained 171 Sichuan wheat accessions and 49 Sichuan wheat landraces. Further analysis showed that TraesCS4A02G343300 and TraesCS7B02G006800 could be candidate genes for QEL.sicau-2SY-4A and QEW.sicau-2SY-7B, respectively. In addition, significant positive correlations between EL and kernel-related traits and the 1,000-grain weight were detected. Collectively, this study broadens our understanding of the genetic basis of wheat embryo size and will be helpful for the further fine-mapping of interesting loci in the future., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Key Message: Combined with BSE-Seq analysis and multiple genetic populations, three genes involved in stripe rust resistance were identified in Chinese wheat landrace Dahongpao, including a novel suppressor on 2BS. Dahongpao (DHP), a landrace of hexaploid wheat in China, exhibits a high degree of stripe rust resistance in the field for many years. In this study, bulked segregant analysis coupled with exome capture sequencing (BSE-Seq) was used to identify genes encoding stripe rust resistance in multiple genetic populations from the cross between DHP and a susceptible hexaploid Australian cultivar, Avocet S (AvS). The most effective QTL in DHP was Yr18, explaining up to 53.08% of phenotypic variance in the F 2:3 families. To identify additional genes, secondary mapping populations SP1 and SP2 were produced by crossing AvS with two resistant lines derived from F 2:3 families lacking Yr18. An all-stage resistance gene, Yr.DHP-6AS, was identified via BSE-Seq analysis of SP1. Combined the recombinant plants from both SP1 and SP2, Yr.DHP-6AS was located between KP6A_1.66 and KP6A_8.18, corresponding to the same region as Yr81. In addition, secondary mapping populations SP3 and SP4 were developed by selfing a segregating line from F 2:3 families lacking Yr18. A novel suppressor gene on chromosome 2BS was identified from DHP for effectively suppressing the resistance of Yr.DHP-6AS in the SP3 and SP4. As a result, the wheat lines carrying both Yr18 and Yr.DHP-6AS show higher level of stripe rust resistance than DHP, providing an effective and simple combination for developing new wheat cultivars with ASR and APR genes. Further, the newly developed KASP markers, KP6A_1.99 and KP6A_5.22, will facilitate the application of Yr.DHP-6AS in wheat breeding via marker-assisted selection., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Grain size is an important trait for crops. The endogenous hormones brassinosteroids (BRs) play key roles in grain size and mass. In this study, we identified an ethyl methylsulfonate (EMS) mutant wheat line, SM482gs , with increased grain size, 1000-grain weight, and protein content, but decreased starch content, compared with the levels in the wild type (WT). Comparative transcriptomic analysis of SM482gs and WT at four developmental stages [9, 15, 20, and 25 days post-anthesis (DPA)] revealed a total of 264, 267, 771, and 1038 differentially expressed genes (DEGs) at these stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) database analysis showed that some DEGs from the comparison at 15 DPA were involved in the pathway of "brassinosteroid biosynthesis," and eight genes involved in BR biosynthesis and signal transduction were significantly upregulated in SM482gs during at least one stage. This indicated that the enhanced BR signaling in SM482gs might have contributed to its increased grain size via network interactions. The expression of seed storage protein (SSP)-encoding genes in SM482gs was upregulated, mostly at 15 and 20 DPA, while most of the starch synthetase genes showed lower expression in SM482gs at all stages, compared with that in WT. The expression patterns of starch synthase genes and seed storage protein-encoding genes paralleled the decreased level of starch and increased storage protein content of SM482gs , which might be related to the increased seed weight and wrinkled phenotype., Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-020-02579-6., Competing Interests: Conflict of interestThe authors declare that there is no conflict of interest., (© King Abdulaziz City for Science and Technology 2021.)

Key Message: Eight major and stably expressed QTL for flag leaf morphology across eleven environments were identified and validated using newly developed KASP markers in seven biparental populations with different genetic backgrounds. Flag leaf morphology is a determinant trait influencing plant architecture and yield potential in wheat (Triticum aestivum L.). A recombinant inbred line (RIL) population with a 55 K SNP-based constructed genetic map was used to map quantitative trait loci (QTL) for flag leaf length (FLL), width (FLW), area (FLA), angle (FLANG), opening angle (FLOA), and bend angle (FLBA) in eleven environments. Eight major QTL were detected in 11 environments with 5.73-54.38% of explained phenotypic variation. These QTL were successfully verified using the newly developed Kompetitive Allele Specific PCR (KASP) markers in six biparental populations with different genetic backgrounds. Among these 8 major QTL, two co-located intervals were identified. Significant interactions for both FLL- and FLW-related QTL were detected. Comparison analysis showed that QFll.sau-SY-2B and QFla.sau-SY-2B are likely new loci. Significant relationships between flag leaf- and yield-related traits were observed and discussed. Several genes associated with leaf development including the ortholog of maize ZmRAVL1, a B3-domain transcription factor involved in regulation of leaf angle, were predicted in physical intervals harboring these major QTL on reference genomes of bread wheat 'Chinese spring', T. turgidum, and Aegilops tauschii. Taken together, these results broaden our understanding on genetic basis of flag leaf morphology and provide clues for fine mapping and marker-assisted breeding wheat with optimized plant architecture for promising loci.

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.

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.

Unfortunately, the author contribution statement was missed out in the original publication. The complete statement is given below.

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.

Two advanced lines (BAd7-209 and BAd7-213) with identical high-molecular-weight glutenin subunit composition were obtained via wide hybridization between low-gluten cultivar chuannong16 (CN16) and wild emmer D97 (D97). BAd7-209 was better than BAd7-213, and both of them were much better than CN16 in a dough quality test. We found that BAd7-209 had more abundant and higher expression levels of low-molecular-weight glutenin subunit (LMW-GS) proteins than those of BAd7-213. Twenty-nine novel LMW-GS genes at Glu - A3 locus were isolated from BAd7-209, BAd7-213 and their parents. We found that all 29 LMW-GS genes possessed the same primary structure shared by other known LMW-GSs. Twenty-seven genes encode LMW-m-type subunits, and two encode LMW-i-type subunits. BAd7-209 had a higher number of LMW-GS genes than BAd7-213, CN16, and D97. Two wild emmer genes MG574329 and MG574330 were present in the two advanced lines. Most of the LMW-m-type genes showed minor nucleotide variations between wide hybrids and their parents that could be induced through the wide hybridization process. Our results demonstrated that the wild emmer LMW-GS alleles could be feasibly transferred and integrated into common wheat background via wide hybridization and the potential value of the wild emmer LMW-GS alleles in breeding programs designed to improve wheat flour quality., Competing Interests: Conflict of interestThe authors declare that there are no conflicts of interest in the reported research.

Key Message: An EMS-induced single-base mutation at a splice site caused abnormal RNA splicing and resulted in the gene inactivation and the lack of Wx-A1 protein in a wheat EMS mutant line. An EMS-mutagenized population was generated using common wheat cv. SM126 consisting of 10,600 M2 plants. One Wx-A1 null mutant was identified through analyses of 390 grains produced from 130 M2 plants using electrophoresis analyses. The Wx-A1 sequences of parental line SM126 and M2-31 mutant were determined as 2781 bp, and there was only one SNP mutation between them. The SNP was a mutation from G to A at nucleotide sequence position 2168 bp (G2168A) downstream of the start codon which was located at the splicing site within the eighth intron. All 52 cDNA transcripts were found to be incorrectly spliced and can be summarized as five types of variations. The deletion of the exon and the exclusion of intron were structural features in abnormal splicing RNA. Together with the prediction of potential splice regulatory motifs, the mutation G2168A happened within the 5' splice site of the eighth intron and destroyed the splice donor site from GU to AU, which may have brought about a barrier against correct RNA splice, and generated abnormal mRNA, which was the mechanism of the inactivation of Wx-A1 in M2-31. The lack of Wx-A1 has resulted in changes in starch properties in the M2-31 mutant, with the reduction in amylose and starch contents. The increased grains hardness was observed in M2-31, which may be related to the lower expression level of Pinb-D1 gene. As the waxy wheat foods have a lot of advantages, the null waxy genes will be widely applied in breeding waxy wheat for varied amylose contents.

Key Message: A major, likely novel stripe rust resistance QTL for all-stage resistance on chromosome arm 1BL identified in a 1.76-cM interval using a saturated linkage map was validated in four populations with different genetic backgrounds. Stripe rust is a globally important disease of wheat. Identification and utilization of new resistance genes are essential for breeding resistant cultivars. Wheat line 20828 has exhibited high levels of stripe rust resistance for over a decade. However, the genetics of stripe rust resistance in this line has not been studied. A set of 199 recombinant inbred lines (RILs) were developed from a cross between 20828 and a susceptible cultivar Chuannong 16. The RIL population was genotyped with the Wheat55K SNP (single nucleotide polymorphism) array and SSR (simple sequence repeat) markers and evaluated in four environments with current predominant Puccinia striiformis f. sp. tritici t races including CYR32, CYR33 and CYR34. Four stable QTL were located on chromosomes 1B (2 QTL), 4A and 6A. Among them, the major QTL, QYr.sicau-1B.1 (LOD = 23-28, PVE = 16-39%), was localized to a 1.76-cM interval flanked by SSR markers Xwmc216 and Xwmc156 on chromosome 1BL. Eight resistance genes were previously identified in the physical interval of QYr.sicau-1B.1. Compared with previous studies, QYr.sicau-1B.1 is a new gene for resistant to stripe rust. It was further verified by analysis of the closely linked SSR markers Xwmc216 and Xwmc156 in four other populations with different genetic backgrounds. QYr.sicau-1B.1 reduced the stripe rust disease index by up to 82.8%. Three minor stable QTL (located on chromosomes 1B, 4A and 6A, respectively) also added to the resistance level of QYr.sicau-1B.1. Our results provide valuable information for further fine mapping and cloning as well as molecular-assisted breeding with QYr.sicau-1B.1.

Key Message: A high-density genetic map constructed with a wheat 55 K SNP array was highly consistent with the physical map of this species and it facilitated the identification of a novel major QTL for productive tiller number. Productive tiller number (PTN) plays a key role in wheat grain yield. In this study, a recombinant inbred line population with 199 lines derived from a cross between '20828' and 'Chuannong16' was used to construct a high-density genetic map using wheat 55 K single nucleotide polymorphism (SNP) array. The constructed genetic map contains 12,109 SNP markers spanning 3021.04 cM across the 21 wheat chromosomes. The orders of the genetic and physical positions of these markers are generally in agreement, and they also match well with those based on the 660 K SNP array from which the one used in this study was derived. The ratios of SNPs located in each of the wheat deletion bins were similar among the wheat 9 K, 55 K, 90 K, 660 K and 820 K SNP arrays. Based on the constructed maps, a novel major quantitative trait locus QPtn.sau-4B for PTN was detected across multi-environments in a 0.55 cM interval on 4B and it explained 17.23-45.46% of the phenotypic variance. Twenty common genes in the physical interval between the flanking markers were identified on chromosome 4B of 'Chinese Spring' and wild emmer. These results indicate that wheat 55 K SNP array could be an ideal tool in primary mapping of target genes and the identification of QPtn.sau-4B laid a foundation for the following fine mapping and cloning work.