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The Ug99 race of stem rust fungus carrying complex virulence combinations continues to pose a significant threat to global wheat production. Concerted research efforts on enhanced surveillance, large-scale deployment of new varieties with combinations of race-specific genes and high to adequate levels of adult plant resistance, together with resistance testing and selection based on functional phenotyping platforms, has significantly reduced the occurrence of epidemics. Promi [Detail] ...
Races belonging to the Ug99 (TTKSK) lineage of the wheat stem rust fungus, carrying complex virulence combinations, and their migration to countries in Africa, Middle East and Asia continue to pose a significant threat to global wheat production. The rapid spread of additional races, e.g., TKTTF or the Digalu lineage, in several countries causing localized epidemics reminds us of the vulnerability of wheat germplasm to stem rust disease, a formidable foe referenced as early as biblical times. A global rust monitoring system reflecting increased surveillance efforts has identified 13 races within the Ug99 lineage in 13 countries and unrelated lineages are emerging, spreading and posing serious threats to wheat production. Race TKTTF has caused localized epidemics in Ethiopia and its variants have been recently implicated in stem rust outbreaks in Europe. Concerted research efforts have resulted in the identification of several new resistance genes and gene combinations for use in breeding. Combining multiple adult plant resistance (APR) genes in high-yielding backgrounds and discovery of new quantitative trait loci conferring stem rust resistance has progressed in the recent years, enhancing the durability of resistance. Effective gene stewardship and new generation breeding materials and cultivars that combine multiple race-specific or minor to intermediate effect APR genes, complemented by active surveillance and monitoring, have helped to limit major epidemics and increase grain yield potential in key target environments.
The publications of the International Wheat Genome Sequencing Consortium (IWGSC) released in August 2018 are reviewed and placed into the context of developments arising from the availability of the high-quality wheat genome assembly.
China and CIMMYT have collaborated on wheat improvement for over 40 years and significant progress has been achieved in five aspects in China. A standardized protocol for testing Chinese noodle quality has been established with three selection criteria, i.e., gluten quality, starch viscosity and flour color are identified as being responsible for noodle quality. Genomic approaches have been used to develop and validate gene-specific markers, leading to the establishment of a KASP platform, and seven cultivars have been released through application of molecular marker technology. Methodology for breeding adult-plant resistance to yellow rust, leaf rust and powdery mildew, based on the pleiotropic effect of minor genes has been established, resulting in release of six cultivars. More than 330 cultivars derived from CIMMYT germplasm have been released and are now grown over 9% of the Chinese wheat production area. Additionally, physiological approaches have been used to characterize yield potential and develop high-efficiency phenotyping platforms. CIMMYT has also provided valuable training for Chinese scientists. Development of climate-resilient cultivars with application of new technology will be the priority for future collaboration.
International Winter Wheat Improvement Program (IWWIP) was established in 1986 between the Government of Turkey and CIMMYT with three main objectives: (1) develop winter/facultative germplasm for Central and West Asia, (2) facilitate global winter wheat germplasm exchange, and (3) training wheat scientists. ICARDA joined the program in 1991 making it a three-way partnership that continues to work effectively. The germplasm developed by IWWIP as well as the winter wheat cultivars and lines received from global cooperators are assembled into international nurseries. These nurseries are offered annually to public and private entities (IWWIP website) and distributed to more than 100 cooperators in all continents. IWWIP impact has primarily been in new winter wheat cultivars combining broad adaptation, high yield potential, drought tolerance and disease resistance. A total of 93 IWWIP cultivars have been released in 11 countries occupying annually an estimated 2.5–3.0 Mha. IWWIP cooperation with researchers in Turkey, Central and West Asia and several US universities has resulted in a number of publications reviewed in this paper. Important IWWIP impacts include national inventories of wheat landraces in Turkey, Tajikistan and Uzbekistan, their collection, characterization, evaluation and utilization.
With the changes of climate and cultivation systems, the Fusarium head blight (FHB) epidemic area in China has extended since 2000 from the reaches of the Yangtze River to the north and west winter wheat region. Breeding for FHB resistance in wheat is an effective way to control the disease. Chinese wheat breeders commenced research on FHB in the 1950s. Sumai 3, Ning 7840, Yangmai 158, Ningmai 9 and other cultivars with improved FHB resistance were developed through standard breeding methods and widely applied in production or breeding programs. In addition to intervarietal crosses, alien germplasm was used to improve FHB resistance of wheat. Addition, substitution and translocation lines with alien chromosomes or chromosome fragments were created to enhance FHB resistance. Somaclonal variation was also used to develop a FHB resistant cv. Shengxuan 3 and other cultivars with moderate resistance to FHB were released by such methods. QTL (quantitative trait loci) for FHB resistance were characterized in cultivars originating from China. The major QTL, Fhb1, was identified on chromosome 3BS in Sumai 3, Ning 894037, Wangshuibai and other Chinese resistant sources. Diagnostic molecular markers for Fhb1 have been applied in wheat breeding and breeding lines with improved FHB resistance and desirable agronomic traits have been obtained. However, breeding for FHB resistance is a long-term task, new technologies are likely to increase the efficiency of this process and better FHB resistance of new cultivars is expected to be achieved within the next decade.
The International Maize and Wheat Improvement Center (CIMMYT) is the global leader in publicly-funded maize and wheat research and in farming systems based on these crops. CIMMYT leads the Global Wheat Program (GWP), which includes some of the largest wheat breeding programs in the world. The GWP has been successful in developing wheat germplasm that is used extensively worldwide. Wheat quality improvement is a central component of all the breeding efforts at CIMMYT and the Wheat Chemistry and Quality Laboratory represents an integral part of the breeding programs. Wheat quality is addressed at CIMMYT over the full range of this very wide and variable concept with milling, processing, end-use and nutritional quality targeted. Wheat progenitors and advanced lines developed by the breeders are assessed for diverse quality attributes, with the aim of identifying those that fulfill the requirements in terms of milling, processing, end-use and nutritional quality in different target regions. Significant research is conducted to make more efficient the integration of wheat quality traits in the breeding programs. The main topics being addressed are (1) methodologies to analyze grain quality traits, (2) genetic control and environmental effects on quality traits, (3) characterization of genetic resources for quality improvement, and (4) diversifying grain properties for novel uses.
Kernel texture (grain hardness) is a fundamental and determining factor related to wheat (Triticum spp.) milling, baking and flour utilization. There are three kernel texture classes in wheat: soft and hard hexaploid (T. aestivum), and very hard durum (T. turgidum subsp. durum). The genetic basis for these three classes lies with the Puroindoline genes. Phenotypically, the easiest means of quantifying kernel texture is with the Single Kernel Characterization System (SKCS), although other means are valid and can provide fundamental material properties. Typical SKCS values for soft wheat would be around 25 and for durum wheat≥80. Soft kernel durum wheat was created via homeologous recombination using the ph1b mutation, which facilitated the transfer of ca. 28 Mbp of 5DS that replaced ca. 21 Mbp of 5BS. The 5DS translocation contained a complete and intact Hardness locus and both Puroindoline genes. Expression of the Puroindoline genes in durum grain resulted in kernel texture and flour milling characteristics nearly identical to that of soft wheat, with high yields of break and straight-grade flours, which had small particle size and low starch damage. Dough water absorption was markedly reduced compared to durum flour and semolina. Dough strength was essentially unchanged and reflected the inherent gluten properties of the durum background. Pasta quality was essentially equal-to-or-better than pasta made from semolina. Agronomically, soft durum germplasm showed good potential with moderate grain yield and resistance to a number of fungal pathogens and insects. Future breeding efforts will no doubt further improve the quality and competitiveness of soft durum cultivars.
Before the advent of the wheat genomic era, a wide range of studies were conducted to understand the chemistry and functions of the wheat storage proteins, which are the major determinants of wheat flour the suitability of wheat flour for various end products, such as bread, noodles and cakes. Wheat grain protein is divided into gluten and non-gluten fractions and the wheat processing quality mainly depends on the gluten fractions. Gluten provides the unique extensibility and elasticity of dough that are essential for various wheat end products. Disulfide bonds are formed between cysteine residues, which is the chemical bases for the physical properties of dough. Based on the SDS-extractability, grain protein is divided into SDS-unextractable polymeric protein (UPP) and SDS-extractable polymeric protein. The percentage of UPP is positively related to the formation of disulfide bonds in the dough matrix. In the wheat genomic era, new glutenins with long repetitive central domains that contain a high number of consensus hexapeptide and nonapeptide motifs as well as high content of cysteine and glutamine residues should be targeted.
Wheat is one of the most important crops in both China and the world, and its domestication can be traced back to ~10000 years ago. However, the history of its origin and utilization in China remains highly ambiguous. Drawing upon the most recent results of taxonomic, genetic, archeological and textual studies focused on the wheat in prehistory, this paper argues that wheat was not domesticated but introduced into China in the late fifth millennium BP. In the subsequent centuries, this exotic crop was quickly utilized as a staple food in northwest China. In contrast, it was not adopted as a staple in the Central Plains until the Han Dynasty (202 BCE–220 CE), which was mainly as a consequence of the living environment, population and innovations in food processing technology.
The application of spectral reflectance indices (SRIs) as proxies to screen for yield potential (YP) and heat stress (HS) is emerging in crop breeding programs. Thus, a comparison of SRIs and their associations with grain yield (GY) under YP and HS conditions is important. In this study, we assessed the usefulness of 27 SRIs for indirect selection for agronomic traits by evaluating an elite spring wheat association mapping initiative (WAMI) population comprising 287 elite lines under YP and HS conditions. Genetic and phenotypic analysis identified 11 and 9 SRIs in different developmental stages as efficient indirect selection indices for yield in YP and HS conditions, respectively. We identified enhanced vegetation index (EVI) as the common SRI associated with GY under YP at booting, heading and late heading stages, whereas photochemical reflectance index (PRI) and normalized difference vegetation index (NDVI) were the common SRIs under booting and heading stages in HS. Genome-wide association study (GWAS) using 18704 single nucleotide polymorphisms (SNPs) from Illumina iSelect 90K identified 280 and 43 marker-trait associations for efficient SRIs at different developmental stages under YP and HS, respectively. Common genomic regions for multiple SRIs were identified in 14 regions in 9 chromosomes: 1B (60–62 cM), 3A (15, 85–90, 101– 105 cM), 3B (132–134 cM), 4A (47–51 cM), 4B (71– 75 cM), 5A (43–49, 56–60, 89–93 cM), 5B (124–125 cM), 6A (80–85 cM), and 6B (57–59, 71 cM). Among them, SNPs in chromosome 5A (89–93 cM) and 6A (80–85 cM) were co-located for yield and yield related traits. Overall, this study highlights the utility of SRIs as proxies for GY under YP and HS. High heritability estimates and identification of marker-trait associations indicate that SRIs are useful tools for understanding the genetic basis of agronomic and physiological traits.