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Bread wheat: a role model for plant domestication and breeding.
Venske, E, Dos Santos, RS, Busanello, C, Gustafson, P, Costa de Oliveira, A
Hereditas. 2019;:16
Abstract
BACKGROUND Bread wheat is one of the most important crops in the world. Its domestication coincides with the beginning of agriculture and since then, it has been constantly under selection by humans. Its breeding has followed millennia of cultivation, sometimes with unintended selection on adaptive traits, and later by applying intentional but empirical selective pressures. For more than one century, wheat breeding has been based on science, and has been constantly evolving due to on farm agronomy and breeding program improvements. The aim of this work is to briefly review wheat breeding, with emphasis on the current advances. DISCUSSION Improving yield potential, resistance/tolerance to biotic and abiotic stresses, and baking quality, have been priorities for breeding this cereal, however, new objectives are arising, such as biofortification enhancement. The narrow genetic diversity and complexity of its genome have hampered the breeding progress and the application of biotechnology. Old approaches, such as the introgression from relative species, mutagenesis, and hybrid breeding are strongly reappearing, motivated by an accumulation of knowledge and new technologies. A revolution has taken place regarding the use of molecular markers whereby thousands of plants can be routinely genotyped for thousands of loci. After 13 years, the wheat reference genome sequence and annotation has finally been completed, and is currently available to the scientific community. Transgenics, an unusual approach for wheat improvement, still represents a potential tool, however it is being replaced by gene editing, whose technology along with genomic selection, speed breeding, and high-throughput phenotyping make up the most recent frontiers for future wheat improvement. FINAL CONSIDERATION Agriculture and plant breeding are constantly evolving, wheat has played a major role in these processes and will continue through decades to come.
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2.
Broadening the bread wheat D genome.
Mirzaghaderi, G, Mason, AS
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2019;(5):1295-1307
Abstract
Although Ae. tauschii has been extensively utilised for wheat breeding, the D-genome-containing allopolyploids have largely remained unexploited. In this review, we discuss approaches that can be used to exploit the D genomes of the different Aegilops species for the improvement of bread wheat. The D genome of allohexaploid bread wheat (Triticum aestivum, 2n = AABBDD) is the least diverse of the three wheat genomes and is unarguably less diverse than that of diploid progenitor Aegilops tauschii (2n = DD). Useful genetic variation and phenotypic traits also exist within each of the wheat group species containing a copy of the D genome: allopolyploid Aegilops species Ae. cylindrica (2n = DcDcCcCc), Ae. crassa 4x (2n = D1D1XcrXcr), Ae. crassa 6x (2n = D1D1XcrXcrDcrDcr), Ae. ventricosa (2n = DvDvNvNv), Ae. vavilovii (2n = D1D1XcrXcrSvSv) and Ae. juvenalis (2n = D1D1XcrXcrUjUj). Although Ae. tauschii has been extensively utilised for wheat breeding, the D-genome-containing allopolyploids have largely remained unexploited. Some of these D genomes appear to be modified relative to the bread wheat and Ae. tauschii D genomes, and others present in the allopolyploids may also contain useful variation as a result of adaptation to an allopolyploid, multi-genome environment. We summarise the genetic relationships, karyotypic variation and phenotypic traits known to be present in each of the D genome species that could be of relevance for bread wheat improvement and discuss approaches that can be used to exploit the D genomes of the different Aegilops species for the improvement of bread wheat. Better understanding of factors controlling chromosome inheritance and recombination in wheat group interspecific hybrids, as well as effective utilisation of new and developing genetics and genomics technologies, have great potential to improve the agronomic potential of the bread wheat D genome.
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3.
Domestication and crop evolution of wheat and barley: Genes, genomics, and future directions.
Haas, M, Schreiber, M, Mascher, M
Journal of integrative plant biology. 2019;(3):204-225
Abstract
Wheat and barley are two of the founder crops of the agricultural revolution that took place 10,000 years ago in the Fertile Crescent and both crops remain among the world's most important crops. Domestication of these crops from their wild ancestors required the evolution of traits useful to humans, rather than survival in their natural environment. Of these traits, grain retention and threshability, yield improvement, changes to photoperiod sensitivity and nutritional value are most pronounced between wild and domesticated forms. Knowledge about the geographical origins of these crops and the genes responsible for domestication traits largely pre-dates the era of next-generation sequencing, although sequencing will lead to new insights. Molecular markers were initially used to calculate distance (relatedness), genetic diversity and to generate genetic maps which were useful in cloning major domestication genes. Both crops are characterized by large, complex genomes which were long thought to be beyond the scope of whole-genome sequencing. However, advances in sequencing technologies have improved the state of genomic resources for both wheat and barley. The availability of reference genomes for wheat and some of its progenitors, as well as for barley, sets the stage for answering unresolved questions in domestication genomics of wheat and barley.
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4.
Non-coeliac gluten sensitivity and the spectrum of gluten-related disorders: an updated overview.
Dale, HF, Biesiekierski, JR, Lied, GA
Nutrition research reviews. 2019;(1):28-37
Abstract
The spectrum of gluten-related disorders includes coeliac disease (CD), wheat allergy (WA) and the suggested entity of non-coeliac gluten sensitivity (NCGS). An increasing number of the world's population are avoiding gluten due to the assumption of health benefits and self-diagnosed gastrointestinal and/or extra-intestinal symptoms. Unlike CD and WA, NCGS is a relatively new entity with an unknown prevalence and mechanisms, complicated by recent literature suggesting that gluten is not the only food component that may trigger symptoms experienced by this group of patients. The term 'non-coeliac wheat sensitivity' has been proposed as a more accurate term, allowing inclusion of other non-gluten wheat components such as fructans and amylase-trypsin inhibitors. There is inconsistent evidence when evaluating the effects of a gluten challenge in patients with suspected NCGS and there is a need for a standardised procedure to confirm the diagnosis, ultimately enabling the optimisation of clinical care. The present review will give an overview of the different gluten-related disorders and discuss the most recent scientific evidence investigating NCGS.
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5.
Hybrid wheat: past, present and future.
Gupta, PK, Balyan, HS, Gahlaut, V, Saripalli, G, Pal, B, Basnet, BR, Joshi, AK
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2019;(9):2463-2483
Abstract
The review outlines past failures, present status and future prospects of hybrid wheat, and includes information on CMS/CHA/transgenic approaches for male sterility, heterotic groups and cost-effective hybrid seed production. Hybrid varieties give increased yield and improved grain quality in both cross- and self-pollinated crops. However, hybrid varieties in self-pollinated crops (particularly cereals) have not been very successful, except for hybrid rice in China. In case of hybrid wheat, despite the earlier failures, renewed efforts in recent years have been made and hybrid varieties with desirable attributes have been produced and marketed in some European countries. This review builds upon previous reviews, with a new outlook and improved knowledge base, not covered in earlier reviews. New technologies have been described, which include the Hordeum chilense-based CMS-fertility restorer system, chromosomal XYZ-4E-ms system and the following transgenic technologies: (1) conditional male sterility involving use of tapetum-specific expression of a gene that converts a pro-toxin into a phytotoxin causing male sterility; (2) barnase-barstar SeedLink system of Bayer CropScience; (3) split-barnase system that obviates the need of a barstar-based male restorer line; and (4) seed production technology of DuPont-Pioneer that makes use of transgenes in production of male-sterile lines, but gives hybrid seed with no transgenes. This review also includes a brief account of studies for discovery of heterotic QTL, genomic prediction of hybrid vigour and the development of heterotic groups/patterns and their importance in hybrid wheat production. The problem of high cost of hybrid seed due to required high seed rate in wheat relative to hybrid rice has also been addressed. The review concludes with a brief account of the current efforts and future possibilities in making hybrid wheat a commercial success.
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6.
Turgor maintenance by osmotic adjustment: 40 years of progress.
Turner, NC
Journal of experimental botany. 2018;(13):3223-3233
Abstract
Osmotic adjustment (OA), the accumulation of solutes in higher plant cells in response to water deficits, was first reported more than four decades ago. Since then, variation in OA among genotypes/cultivars in response to drought has been reported in many crop plants, but its role in maintaining growth and yield in water-limited environments has been questioned. The role of OA in the physiological and agronomic adaptation to water stress of crops, the methods of reliably measuring the degree of OA among genotypes or species, the range of OA in many studies, and its impact on grain yield in water-limited environments are reviewed. The genetics of OA has received limited study, and the breeding and selection for high OA has only resulted in the release of one commercial cultivar of wheat as far as is known. The reasons for the limited interest in breeding for the OA trait are discussed.
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7.
Wheat seed transcriptome reveals genes controlling key traits for human preference and crop adaptation.
Henry, RJ, Furtado, A, Rangan, P
Current opinion in plant biology. 2018;(Pt B):231-236
Abstract
Analysis of the transcriptome of the developing wheat grain has associated expression of genes with traits involving production (e.g. yield) and quality (e.g. bread quality). Photosynthesis in the grain may be important in retaining carbon that would be lost in respiration during grain filling and may contribute to yield in the late stages of seed formation under warm and dry environments. A small number of genes have been identified as having been selected by humans to optimize the performance of wheat for foods such as bread. Genes determining flour yield in milling have been discovered. Hardness is explained by variations in expression of pin genes. Knowledge of these genes should dramatically improve the efficiency of breeding better climate adapted wheat genotypes.
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8.
Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement.
Alvarez, JB, Guzmán, C
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2018;(2):225-251
Abstract
The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality. Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.
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9.
A review of wheat diseases-a field perspective.
Figueroa, M, Hammond-Kosack, KE, Solomon, PS
Molecular plant pathology. 2018;(6):1523-1536
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Abstract
Wheat is one of the primary staple foods throughout the planet. Significant yield gains in wheat production over the past 40 years have resulted in a steady balance of supply versus demand. However, predicted global population growth rates and dietary changes mean that substantial yield gains over the next several decades will be needed to meet this escalating demand. A key component to meeting this challenge is better management of fungal incited diseases, which can be responsible for 15%-20% yield losses per annum. Prominent diseases of wheat that currently contribute to these losses include the rusts, blotches and head blight/scab. Other recently emerged or relatively unnoticed diseases, such as wheat blast and spot blotch, respectively, also threaten grain production. This review seeks to provide an overview of the impact, distribution and management strategies of these diseases. In addition, the biology of the pathogens and the molecular basis of their interaction with wheat are discussed.
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10.
Celiac disease and non-celiac gluten or wheat sensitivity and health in later life: A review.
Bathrellou, E, Kontogianni, MD, Panagiotakos, DB
Maturitas. 2018;:29-33
Abstract
Celiac disease (CD) and non-gluten (or wheat) sensitivity (NCGS) are two gluten-related disorders, the treatment of which relies on dietary withdrawal of gluten (absolute and lifelong in the case of CD patients). However, these conditions differ in their pathophysiology and impact on health. CD is an autoimmune disorder of the intestine, and is associated with a wide range of disorders, pre- and post-diagnosis. Its autoimmune and inflammatory nature raises concerns about its potential effects on mortality and morbidity. Here we review the data on the health impact CD or NCGS may have prospectively, and report on the role of a gluten-free diet (GFD) in this respect. Since study designs have been heterogeneous, we focus on studies of treated patients with a biopsy-proven diagnosis of CD, to eliminate possible bias from misdiagnosis. The review revealed a moderately increased mortality risk among CD patients, mainly attributed to cardiovascular disease and malignancy. Other long-term morbidities of CD include autoimmune disorders, nutritional deficiencies, impaired bone health, reproductive abnormalities, and neurologic and neuropsychiatric disorders, which are substantially improved, and some of them even completely treated, after strict adherence to a GFD. For NCGS, the literature is too limited and its long-term complications are unknown.