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Common buckwheat (Fagopyrum esculentum Moench 2n = 2x = 16) is a typical outcrossing crop, which needs pollination by insects, such as bees, for seed setting. It has an excellent nutritional profile, with a well-balanced amino acid composition, is rich in vitamins, fiber, and minerals, and has a high antioxidant potential. It is used in many traditional foods such as soba (Japanese noodles). However, buckwheat has many issues, such as a low lodging tolerance and being a common allergen, which need to be overcome to increase the yield and consumption.

(R. Ohsawa: University of Tsukuba; Y. Yasui: Kyoto University; R. Takeshima, Y. Horikoshi and K. Matsui: NARO, JAPAN)

In this review, the current status and prospects of common buckwheat (Fagopyrum esculentum Moench.) breeding in Japan are summarized. The varieties that have been registered in Japan so far are introduced with details regarding their breeding source populations and breeding methods. Because the main breeding method used for common buckwheat is mass selection, the merits and demerits of this method are explored from the perspective of heritability. Although there are many breeding objectives in common buckwheat, high yield and yield stability are discussed here. Regarding the potential of common buckwheat breeding in the future, the prospects of effective exploitation of self-fertility and selection based on genomic information are examined.

Genotyping is an essential procedure for identifying agronomically useful genes and analyzing population structure. Various types of genetic marker systems have been developed in common buckwheat (Fagopyrum esculentum Moench). In the 1980s, morphological and allozyme markers were used to construct linkage maps. Until the early 2000s, allozyme markers were widely used in population genetics studies. Such studies demonstrated that cultivated common buckwheat likely originated in the Sanjiang area of China. In the late 1990s and early 2000s, advances in PCR technology led to the development of various DNA marker systems for use in linkage mapping. However, PCR-based markers did not completely cover the genome, making genetic analysis of buckwheat challenging. The subsequent development of next generation sequencing, a game-changing technology, has allowed genome-wide analysis to be performed for many species. Indeed, 8,884 markers spanning 756 loci were recently mapped onto eight linkage groups of common buckwheat; these markers were successfully used for genomic selection to increase yield. Furthermore, draft genome sequences are now available in the Buckwheat Genome DataBase (BGDB). In this review, I summarize advances in the breeding and genetic analysis of common buckwheat based on contemporary genetic marker systems.

Minor and pseudo-cereals, which can grow with lower input and often produce specific nutrients compared to major cereal crops, are attracting worldwide attention. Since these crops generally have a large genetic diversity in a breeding population, rapid genetic improvement can be possible by the application of genomics-assisted breeding methods. In this review, we discuss studies related to biparental quantitative trait locus (QTL) mapping, genome-wide association study, and genomic selection for minor and pseudo-cereals. Especially, we focus on the current progress in a pseudo-cereal, buckwheat. Prospects for the practical utilization of genomics-assisted breeding in minor and pseudo-cereals are discussed including the issues to overcome especially for these crops.

Common buckwheat (Fagopyrum esculentum Moench 2n = 2x = 16) is an outcrossing crop with heteromorphic self-incompatibility due to its distylous flowers, called pin and thrum. In pin plants, a long style is combined with short stamens and small pollen grains; in thrum plants, a short style is combined with long stamens and large pollen grains. Both the intra-morph self-incompatibility and flower morphology are controlled by a single genetic locus named the S locus; thrum plants are heterozygous (Ss) and pin plants are homozygous recessive (ss) at this locus. Self-incompatibility is an obstacle for establishing pure lines and fixation of agronomically useful genes. Elucidation of the molecular mechanism of heterostylous self-incompatibility of common buckwheat has continued for a quarter of a century. Recent advances in genomic and transcriptomic analyses using next-generation sequencing have made it possible to determine the genomic region harboring the buckwheat S locus and to identify novel genes at this locus. In this review, we summarize the current knowledge on buckwheat heterostyly gained from conventional and molecular genetics and genomics. We also discuss the application of these studies to breeding of common buckwheat.

Common buckwheat is recognized as a healthy food because its seed contains large amounts of protein, minerals, and rutin. However, the yielding ability of common buckwheat is lower than that of other major crops. The short growing period, moisture injury, occurrence of sterile seeds due to lack of flower-visiting insects, and yield loss due to lodging and shattering cause low and unstable grain yield. Therefore, many common buckwheat breeders have tried to increase yielding ability by improving various characteristics. Recently, new breeding objectives for improving yielding ability by increasing preharvest sprouting resistance; reducing shattering loss; introducing self-compatibility; the ecotype, and semidwarf have been reported. In this review, we introduce the research on the important agronomic characteristics, preharvest sprouting resistance, ecotype and ecological differentiation, shattering resistance, and lodging resistance in common buckwheat.

Buckwheat is an important crop globally. It has been processed into cereal grain, noodles, confectionery, bread, and fermented foods for many years. Buckwheat production and processing has supported local economies and is deeply related to the culture of some regions. Buckwheat has many unique traits as a food, with a good flavor and color. In addition, buckwheat is also a healthy food because it contains bioactive compounds that have anti-oxidative, anti-hypertensive, and anti-obesity properties. Therefore, breeding of buckwheat for quality is an important issue to be addressed. Compared to other crops, there is still a lack of basic information on quality, including bioactive compounds generation and enhancement. However, some mechanisms for modifying and improving the quality of buckwheat varieties have recently been identified. Further, some varieties with improved quality have recently been developed. In this review, we summarize the issues around buckwheat quality and review the present status and future potential of buckwheat breeding for quality.

Common buckwheat (Fagopyrum esculentum Moench, CB) and Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn., TB) are used in human nutrition. The idea to screen in the haploid phase for genes affecting low amylose concentration opens the possibility for the effective search of low amylose (waxy) genotypes in CB populations. Self-pollinated homozygous plants of TB might allow us to use a part of endosperm for screening of amylose content. Phenolic substances have a significant inhibitory effect on the digestion of CB and TB proteins, thus metabolites may have impact on protein digestibility. Digestion-resistant peptides are largely responsible for the bile acid elimination. Breeding to diminish polyphenols and anti-nutritional substances might have negative effects on the resistance of plants against pests, diseases and UV-radiation. Bread and pasta are popular CB and TB dishes. During dough making most of CB or TB rutin is degraded to quercetin by rutin-degrading enzymes. The new trace-rutinosidase TB variety makes possible making TB bread with considerable amount of rutin, preserving the initial rutin from flour. Breeding CB and TB for larger embryos would make it possible to increase protein, rutin, and essential minerals concentration in CB and TB grain.

Buckwheat contains an abundance of antioxidants such as polyphenols and is considered a functional food. Among polyphenols, flavonoids have multiple functions in various aspects of plant growth and in flower and leaf colors. Flavonoids have antioxidant properties, and are thought to prevent cancer and cardiovascular disease. Here, we summarize the flavonoids present in various organs and their synthesis in buckwheat. We discuss the use of this information to breed highly functional and high value cultivars.

Buckwheat allergy is an immediate hypersensitivity reaction that includes anaphylaxis mediated by specific IgE antibodies. Several IgE-binding proteins in common buckwheat have been reported to be possible clinically relevant buckwheat allergens. Although common buckwheat is popularly consumed in Asia, buckwheat allergy is becoming a serious problem not only in Asia but also in Europe. In addition, common buckwheat has also been found to be a causative agent of allergic symptoms in animals. In recent years, in addition to conventional food allergy testing methods, the development of component-resolved diagnosis (CRD) has improved the diagnostic accuracy of food allergy. The identification of allergens is essential for the construction of CRD. In this review, we introduce the different types of buckwheat allergens and discuss how each buckwheat allergen contributes to the diagnosis of buckwheat allergy. We also present the analysis of buckwheat allergen that will help reduce the allergenicity of common buckwheat and reduce buckwheat allergen molecules. These findings may be beneficial in overcoming buckwheat allergies in humans and animals.

Fagopyrum (Polygonaceae) is a small genus including less than 30 species, mostly endemic to southern China. The genus includes two cultivated species, common buckwheat F. esculentum and Tartary buckwheat F. tataricum. Fagopyrum is clearly distinguished from other genus in Polygonaceae by the central position of embryo in achene. The genus is divided into two major groups, namely the cymosum group and the urophyllum group, based on morphological characters and molecular systematics. In the last three decades the number of species in the genus has doubled by the discovery of new species by Japanese and Chinese groups. Most of them are revealed to be included in the urophyllum group based on morphological and molecular genetic analyses. Molecular systematic surveys have also detected inappropriate treatment of some non-Fagopyrum species as new species or combination in the genus.

Ecotype breeding is a key technology in common buckwheat (Fagopyrum esculentum Moench) for the breeding of highly adaptive cultivars and their introduction to other cultivation areas. However, the details of the relationship between photoperiod sensitivity and ecotype remain unclear. Here, we evaluated photoperiod sensitivity in 15 landraces from different parts of Japan, and analyzed quantitative trait loci (QTLs) for photoperiod sensitivity using two F₂ segregating populations derived from the crosses between self-compatible lines (‘Kyukei SC2’ or ‘Buckwheat Norin PL1’, early days-to-flowering) and allogamous plants (intermediate or late days-to-flowering). We clarified that (1) photoperiod sensitivity and differences in ecotype are closely related; (2) photoperiod sensitivity is controlled by several QTLs common among population of different ecotypes; and (3) orthologues of GIGANTEA and EARLY FLOWERING 3 will be useful markers in future detailed elucidation of the photoperiod sensitivity mechanism in common buckwheat. This study provides the basis for genomics-assisted breeding for local adaptation and ecotype breeding in common buckwheat.

Common buckwheat (Fagopyrum esculentum) is a heterostylous self-incompatible (SI) species with two different flower morphologies, pin and thrum. The SI trait is controlled by a single gene complex locus, S. Self-compatible (SC) lines were developed by crossing F. esculentum and F. homotropicum; these lines have an SC gene, S^h, which is dominant over the s allele and recessive to the S allele. S-ELF3 has been identified as a candidate gene in the S locus and is present in the S and S^h but not s alleles. A single-nucleotide deletion in the S-ELF3 gene of the S^h allele results in a frame shift. To develop co-dominant markers to distinguish between S^hS^h and S^hs plants, we performed a next-generation sequencing analysis in combination with bulked-segregant analysis. We developed four co-dominant markers linked to the S locus. We investigated the polymorphism frequency between a self-compatible line and leading Japanese buckwheat cultivars. Linkage between a developed sequence-tagged-site marker and flower morphology was confirmed using more than 1000 segregating plants and showed no recombination. The developed markers would be useful for buckwheat breeding and also to produce lines for genetic analysis such as recombinant inbred lines.

The zero-repeat subunit of 13S globulin, which lacks tandem repeat inserts, is trypsin-resistant and suggested to show higher allergenicity than the other subunits in common buckwheat (Fagopyrum esculentum Moench). To evaluate allelic variations and find novel alleles, the diversity of the zero-repeat genes was examined for two Japanese elite cultivars and 15 Pakistani landraces. The results demonstrated that two new alleles GlbNA1 and GlbNC1, plus three additional new alleles GlbNA2, GlbNA3, and GlbND, were identified besides the already-known GlbNA, GlbNB, and GlbNC alleles. In the Pakistani landraces, GlbNA was the most dominant allele (0.60–0.88 of allele frequency) in all except one landrace, where GlbNB was the most dominant allele (0.50 of allele frequency). Similar to GlbNC, the alleles GlbNA2 and GlbNA3 had extra ~200 bp MITE-like sequences around the stop codon. Secondary structure predictions of a sense strand demonstrated that the extra ~200 bp sequences of GlbNC, GlbNA2, and GlbNA3 can form rigid hairpin structures with free energies of –78.95, –67.06, and –29.90 kcal/mol, respectively. These structures may affect proper transcription and/or translation. In the GlbNC homozygous line, no transcript of a zero-repeat gene was detected, suggesting the material would be useful for developing hypoallergenic buckwheat.

Buckwheat (Fagopyrum esculentum) is cultivated worldwide and its flour is used in a variety of food products. Although functional analyses of genes in buckwheat are highly desired, reliable methods to do it have yet to be developed. In this study we established a simple and efficient transient gene expression system using buckwheat protoplasts isolated from young hypocotyls using 96-well plates as a high-throughput platform. The transformation efficiency was comparable with that of similar systems, such as Arabidopsis mesophyll protoplasts. Stable results were obtained in a typical example of the experiment to examine transcription factor activity. This system shows potential for the large-scale analysis of gene function using protoplast isolated from fewer and younger plants than the conventional system and may provide novel information for efficient buckwheat breeding.