Common wheat is the major cereal crop that underpins the food safety of China. Both winter wheat and spring wheat are grown on ~24?million?ha. This review aims to summarize the current status of wheat production and breeding progress in the northern wheat production areas of the country, and to review recently advanced technologies being applied in wheat breeding, including the use of dwarf-male-sterile (DMS) wheat, speed breeding and specialized wheat breeding SNP chips. Crossing is the initial step in most breeding programs. DMS wheat is a convenient tool for large scale production of hybrid seed. Speed breeding or accelerated generation turnover attempts to reduce the time taken in cultivar development. Several different SNP chips are high-throughput, genome-wide genotyping platforms for breeding and research.
The objective of this paper is to review progress made in wheat breeding for Fusarium head blight (FHB) resistance in China, the United States of America (USA), and Canada. In China, numerous Chinese landraces possessing high levels of FHB resistance were grown before the 1950s. Later, pyramiding multiple sources of FHB resistance from introduced germplasm such as Mentana and Funo and locally adapted cultivars played a key role in combining satisfactory FHB resistance and high yield potential in commercial cultivars. Sumai 3, a Chinese spring wheat cultivar, became a major source of FHB resistance in the USA and Canada, and contributed to the release of more than 20 modern cultivars used for wheat production, including the leading hard spring wheat cultivars Alsen, Glenn, Barlow and SY Ingmar from North Dakota, Faller and Prosper from Minnesota, and AAC Brandon from Canada. Brazilian wheat cultivar Frontana, T. dicoccoides and other local germplasm provided additional sources of resistance. The FHB resistant cultivars mostly relied on stepwise accumulation of favorable alleles of both genes for FHB resistance and high yield, with marker-assisted selection being a valuable complement to phenotypic selection. With the Chinese Spring reference genome decoded and resistance gene Fhb1 now cloned, new genomic tools such as genomic selection and gene editing will be available to breeders, thus opening new possibilities for development of FHB resistant cultivars.
We report on pyramiding different disease resistance genes against fungal pathogens in Canadian winter wheat germplasm based on available DNA markers and gene sequences. Genetic resistance represents a safe, economical and ecological method for protecting plants, growers and the health of consumers. Major diseases of wheat on the Canadian Prairies are common bunt, rusts (leaf, stem and stripe) and Fusarium head blight. Over the years markers for resistance genes against these diseases have been identified and used by the international wheat community. We describe markers that we have used to pyramid different resistance genes and indicate their presence in Canadian winter wheat cultivars issued from the winter wheat breeding program at the Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, the only winter wheat breeding program in Western Canada actively delivering new varieties for all regions of the Canadian Prairies. The sources of resistance and identities of PCR primers and amplification conditions are indicated to enable the transfer and pyramiding of different resistance (R) genes to breeding lines. We conclude by reviewing new tools for identifying R genes in wheat and indicate how mutagenesis and gene editing can help future efforts to extend the protection offered by known R genes.
Herbicide resistance in crops has extended the scope of herbicide applications to control weeds. The introduction of herbicide resistant crops resulted in a major shift in the way that herbicides are used in many crops, but not necessarily increased the prevalence of herbicide use, especially in wheat. Wheat is one of the most widely grown crops in the world and currently only two major herbicide-resistant wheat groups have been commercialized to manage weeds in a cost-effective manner. However, sustainable wheat production is threatened by the expanding occurrence of herbicide-resistant weed populations with limited efforts to discover new herbicide molecules. Selective control of certain problematic weeds in wheat was impossible until development and introduction of the technologies, Clearfield and CoAXium Production Systems. However, the current limitations of reliance on specific herbicides and evolution of resistant weeds mandate precautions and considerations when using these systems to prevent the loss of existing herbicide resources and continue sustainable wheat production. The focus of this review is to provide an overview of natural pre-existing herbicide resistance and development of herbicide-resistant technologies in wheat. The mechanisms of resistance to herbicides in wheat as well as the weed populations in wheat cropping systems, and implications for weed management are discussed.
Stripe rust and powdery mildew are both devastating diseases for durum and common wheat. Pyramiding of genes conferring resistance to one or more diseases in a single cultivar is an important breeding approach to provide broader spectra of resistances in wheat improvement. A new powdery mildew resistance gene originating from wild emmer (Triticum turgidum var. dicoccoides) backcrossed into common wheat (T. aestivum) line WE35 was identified. It conferred an intermediate level of resistance to Blumeria graminis f. sp. tritici isolate E09 at the seedling stage and a high level of resistance at the adult plant stage. Genetic analysis showed that the powdery mildew resistance in WE35 was controlled by a dominant gene designated Pm64. Bulked segregant analysis (BSA) and molecular mapping indicated that Pm64 was located in chromosome bin 2BL4-0.50-0.89. Polymorphic markers were developed from the corresponding genomic regions of Chinese Spring wheat and wild emmer accession Zavitan to delimit Pm64 to a 0.55?cM genetic interval between markers WGGBH1364 and WGGBH612, corresponding to a 15?Mb genomic region on Chinese Spring and Zavitan 2BL, respectively. The genetic linkage map of Pm64 is critical for fine mapping and cloning. Pm64 was completely linked in repulsion with stripe rust resistance gene Yr5. Analysis of a larger segregating population might identify a recombinant line with both genes as a valuable resource in breeding for resistance to powdery mildew and stripe rust.
Powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a prevalent disease in common wheat (Triticum aestivum L.) and causes serious yield losses worldwide. We used a map-based approach to clone the major broad-spectrum powdery mildew resistance gene PmCH1357 from wheat breeding line CH1357. PmCH1357 was mapped to a 526?kb region containing only TraesCS5D01G044600. The TraesCS5D01G044600 sequence of the susceptibility allele in Taichung 29 (TC29) was identical to that in Chinese Spring, whereas the sequence of the resistance allele in CH1357 was identical to Pm2a previously cloned from the germplasm Ulka/*8Cc. The susceptibility allele in TC29 contained a 7?bp deletion in exon 1, resulting in loss of 856 of the 1277 amino acids in the predicted nucleotide-binding domain leucine-rich repeat containing Pm2a protein. PmCH1357/Pm2a sequence was also isolated from the Chinese wheat landraces and cultivars that were previously reported to possess the resistance gene Pm2b, Pm2c, PmLX66, or PmND399. The PmCH1357/Pm2a resistance allele was present in 10 of 495 accessions in core germplasm and contemporary cultivars from China and the USA. A newly developed diagnostic marker for the 7?bp InDel in the resistance gene can be used to eliminate the susceptibility allele in wheat breeding programs.
Epidemics of Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe, in wheat cause significant reductions in grain yield and quality. Numerous quantitative trait loci (QTL) for FHB resistance have been reported from Chinese sources. However, the relationships among QTL from different landraces have not been characterized. We earlier mapped QTL for FHB resistance using low-density maps developed from five recombinant inbred line (RIL) populations involving Chinese landraces ‘Haiyanzhong’ (HYZ), ‘Wangshuibai’ (WSB), ‘Baishanyuehuang’ (BSYH), ‘Huangfangzhu’ (HFZ), and ‘Huangcandou’ (HCD) as FHB resistant parents. In this study, we used maps of single nucleotide polymorphisms (SNP) developed from the five populations and identified 31 QTL on 16 chromosomes; 10 QTL were new. We constructed a consensus map and identified six meta-QTL (MQTL) and SNP within the MQTL regions using meta-analysis. Two of the MQTL were on chromosome 3BS (3BSd and 3BSc), and one on each of chromosomes 3A, 2D, 3D, and 4D. Twenty-two SNP closely linked to MQTL were converted into breeder friendly Kompetitive Allele Specific Polymerase Chain Reaction (KASP) assays, which should be useful for marker-assisted selection in breeding programs.
The gene Fhb1 has been used in many countries to improve wheat Fusarium head blight (FHB) resistance. To make better use of this gene in the Yellow-Huai River Valleys Winter Wheat Zone (YHWZ), the most important wheat-producing region of China, it is desirable to elucidate its effects on FHB resistance and agronomic traits in different genetic backgrounds. Based on a diagnostic marker for Fhb1, six BC2 populations were developed by crossing dwarf-male-sterile (DMS)-Zhoumai 16 to three Fhb1 donors (Ningmai 9, Ningmai 13, and Jianyang 84) and backcrossing to Zhoumai 16 and Zhoumai 16's derivative cultivars (Lunxuan 136 and Lunxuan 13) using marker-assisted backcross breeding. The progenies were assessed for FHB resistance and major agronomic traits. The Fhb1 alleles were identified using the gene-specific molecular marker. The plants with the Fhb1-resistant genotype (Fhb1-R) in these populations showed significantly fewer infected spikelets than those with the Fhb1-susceptible genotype (Fhb1-S). When Lunxuan 136 was used as the recurrent parent, Fhb1-R plants showed significantly fewer infected spikelets per spike than Fhb1-R plants produced using Lunxuan 13 as the recurrent parent, indicating that the genetic backgrounds of Fhb1 influence the expression of FHB resistance. Fhb1-R plants from the DMS-Zhoumai 16/Ningmai 9//Zhoumai 16/3/Lunxuan 136 population showed the highest FHB resistance among the six populations and a significantly higher level of FHB resistance than the moderately susceptible control Huaimai 20. No significant phenotypic differences between Fhb1-R and Fhb1-S plants were observed for the eight agronomic traits investigated. These results suggest that it is feasible to improve FHB resistance of winter wheat without reducing yield potential by introgressing Fhb1 resistance allele into FHB-susceptible cultivars in the YHWZ.
Tan spot (TS) and Septoria nodorum blotch (SNB), caused by Pyrenophora tritici-repentis and Parastagonospora nodorum, respectively, are important fungal leaf-spotting diseases of wheat that cause significant losses in grain yield. In this study, two recombinant inbred line populations, ‘Bartai’?×?‘Ciano T79’ (referred to as B?×?C) and ‘Cascabel’?×?‘Ciano T79’ (C?×?C) were tested for TS and SNB response in order to determine the genetic basis of seedling resistance. Genotyping was performed with the DArTseq genotyping-by-sequencing (GBS) platform. A chromosome region on 5AL conferred resistance to TS and SNB in both populations, but the effects were larger in B?×?C (R2?=?11.2%-16.8%) than in C?×?C (R2?=?2.5%-9.7%). Additionally, the chromosome region on 5BL (presumably Tsn1) was significant for both TS and SNB in B?×?C but not in C?×?C. Quantitative trait loci (QTL) with minor effects were identified on chromosomes 1B, 2A, 2B, 3A, 3B, 4D, 5A, 5B, 5D, 6B, and 6D. The two CIMMYT breeding lines ‘Bartai’ and ‘Cascabel’ contributed resistance alleles at both 5AL and 5BL QTL mentioned above. The QTL on 5AL showed linkage with the Vrn-A1 locus, whereas the vrn-A1 allele conferring lateness was associated with resistance to TS and SNB.
Thinopyrum intermedium (2n?=?6x?=?42, JJJsJsStSt) has been hybridized extensively with common wheat and has proven to be a valuable germplasm source for improving disease resistance, quality attributes, and yield potential in wheat. We characterized new disease resistant wheat-Th. intermedium derivatives A1082 and A5-5 using sequential multi-color fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A1082 was identified as a wheat-Th. intermedium 3J disomic addition line, and A5-5 was a T4BS·5JsL homozygous Robertsonian translocation line. Seventy-one and 106 pairs of primers amplified Th. intermedium-specific bands allowing chromosomes 3J and 5Js to be tracked, respectively. A new oligonucleotide probe, Oligo-6H-2-100, was developed for FISH labeling of the subterminal region of the long arm of chromosome 5Js. Both lines were highly resistant to stripe rust pathogen races prevalent in Chinese field screening nurseries. A5-5 also displayed a significant increase in tiller number compared to its wheat parent. The new lines can be exploited as useful germplasms for wheat improvement.
Grain Weight 8 (GW8) in rice is a SQUAMOSA Promoter-Binding Protein-Like (SPL) family transcription factor with multiple biological functions. In this study, three GW8 homoeologs were cloned from homoeologous group 7 chromosomes of wheat. Subcellular localization and trans-activation activity assays suggested that TaGW8 is a transcriptional activator. TaGW8 genes were preferentially expressed in young spikes and developing grains. Ectopic expressions of TaGW8 in Arabidopsis and rice resulted in enhanced vegetative growth, earlier flowering and larger seeds. TaGW8-7A was the most highly variable of the three homoeologs with four haplotypes (Hap-1/2/3/4). TaGW8-7B had two haplotypes (Hap-L/H). TaGW8-7A-Hap-2 was associated with high thousand-grain weight (TGW) and large kernel length and showed higher transcriptional levels and binding activity than the other haplotypes. The high frequency of TaGW8-7A-Hap-2 in Chinese wheat populations suggested that it had been extensively selected in breeding. This haplotype showed a high potential for exploitation in global wheat breeding because its frequency was low in exotic germplasm. TaGW8-7B-Hap-H produced abundant transcripts and was associated with early heading and maturity, less tiller number and high TGW. This haplotype might be suitable for multiple cropping systems due to short wheat season. In this study we identified sub-functionalization among TaGW8 homoeologs and obtained functional molecular markers that can be used in breeding for high grain yield.
Grain yield in cereal crops is a complex trait controlled by multiple genes and influenced by developmental processes and environment. Here we report the effects of alleles Rht8 and Ppd-D1a on plant height, time to heading, and grain yield and its component traits. Association analysis and quantitative trait locus mapping using phenotypic data from 15 environments led to the following conclusions. First, both Rht8 and Ppd-D1a reduce plant height. However, Ppd-D1a but not Rht8 causes earlier heading. Second, both Rht8 and Ppd-D1a promote grain yield and affect component traits. Their combined effects are substantially larger than those conferred by either allele alone. Third, promotion of grain yield by Rht8 and Ppd-D1a is through increasing fertile spikelet number. We speculate that Rht8 and Ppd-D1a act independently and additively in control of plant height, grain yield and yield component. Combination of the two alleles is desirable for adjusting plant height and enhancing grain yield and abiotic stress tolerance.
Cold tolerance of crop plants influences survival and productivity under low-temperature conditions. Elucidation of molecular mechanisms underlying low temperature tolerance could be helpful in breeding. In this study, we used integrated transcriptomics and metabolomics analyses to investigate changes in gene/metabolite activity in a winter-hardy wheat cultivar of (cv. Jing 411) when subjected to sold stress. The 223 metabolites mainly enriched during cold acclimation included carbohydrates, flavonoids, and amino acids. Eight common metabolites had altered abundance following freezing treatment; six increased and two decreased. Transcriptome analysis revealed that 29,066 genes were differentially expressed in wheat crowns after cold acclimation compared to the non-acclimated control. Among them, 745 genes were up-regulated following freezing treatment, suggesting substantial change in expression of a large quantity of genes upon cold acclimation and freezing treatment, which impacts on the modified metabolites. Integrated analysis of gene expression and metabolite profiles revealed that the abscisic acid (ABA)/jasmonic acid (JA) phytohormone signaling and proline biosynthesis pathways were significantly modulated under cold acclimation and freezing treatments. Our results indicated that low-temperature stress induced substantial changes in both transcriptomes and metabolomes. Critical pathways associated with ABA/JA signaling and proline biosynthesis played important roles in regulating cold tolerance in wheat.
