Background: Tartary buckwheat (Fagopyrum tataricum) is a nutritionally balanced and flavonoid-rich crop plant that has been in cultivation for 4000 years and is now grown globally. Despite its nutraceutical and agricultural value, the characterization of its genetics and its domestication history is limited.Results: Here, we report a comprehensive database of Tartary buckwheat genomic variation based on whole-genome resequencing of 510 germplasms. Our analysis suggests that two independent domestication events occurred in southwestern and northern China, resulting in diverse characteristics of modern Tartary buckwheat varieties. Genome-wide association studies for important agricultural traits identify several candidate genes, includingFtUFGT3andFtAP2YT1that significantly correlate with flavonoid accumulation and grain weight, respectively.Conclusions: We describe the domestication history of Tartary buckwheat and provide a detailed resource of genomic variation to allow for genomic-assisted breeding in the improvement of elite cultivars.

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Buckwheat (Fagopyrum esculentum) is recognized as an important traditional crop in some regions, and its taste is an important characteristic. Of the three cultivated buckwheat species, Tartary buckwheat (Fagopyrum tataricum) and perennial buckwheat (Fagopyrum cymosum) have strong bitterness in their seeds, which has prevented the wider use of the seeds of these varieties. In Tartary buckwheat, some studies have focused on the cause of strong bitterness generation. Tartary buckwheat seeds contain large amounts of the functional compounds rutin and rutinosidase, and rutin hydrolysis by rutinosidase has been found to be the trigger of rutin hydrolysis. Therefore, a variety with only a trace of rutinosidase and with reduced bitterness is required. The rutinosidase in Tartary buckwheat seeds consists of two major isozymes with very similar enzymatic characteristics, which can hydrolyze flour rutin within several minutes after the addition of water. Recently, the trace-rutinosidase variety Manten-Kirari in Tartary buckwheat was developed. The trace-rutinosidase characteristics were dominated by a single recessive gene. In ‘Manten-Kirari’ dough and foods, such as breads, confectionaries, and noodles, the rutin residual ratio was higher and bitterness was reduced compared to that of the normal-rutinosidase variety. In this review, we summarize the detailed research on the breeding of buckwheat related to reducing bitterness and rutin hydrolysis.

In a screening of about 500 lines of Tartary buckwheat, we identified lines that contained no detectable rutinosidase isozymes using an in-gel detection assay. We confirmed that seeds of these individuals had only a trace level of in-vitro rutinosidase activity. To investigate the heritability of the trace-rutinosidase characteristic, we analyzed the progeny of crosses between rutinosidase trace-lines, ‘f3g-162’, and the ‘Hokkai T8’. The F₂ progeny clearly divided into two groups: those with rutinosidase activity under 1.5 nkat/g seed (trace-rutinosidase) and those with activity over 400 nkat/g seed (normal rutinosidase). The segregation pattern of this trait in F₂ progeny exhibited 1 : 3 ratio (trace-rutinosidase : normal rutinosidase), suggesting that the trace-rutinosidase trait is conferred by a single recessive gene; rutinosidase-trace A (rutA). In addition, sensory panelists evaluated the bitterness of flour from trace-rutinosidase individuals and did not detect bitterness, whereas flour from normal rutinosidase individuals was found to have strong bitterness. Although at least three bitter compounds have been reported in Tartary buckwheat seeds, our present findings indicate that rutin hydrolysis is the major contributing factor to bitterness. In addition, the trace-rutinosidase line identified here, ‘f3g-162’, is a promising material for generating a non-bitter Tartary buckwheat variety.

In order to investigate the toxicity of rutin-rich dough from the Tartary buckwheat variety ‘Manten-Kirari,’ acute and subacute toxicity studies (10,000 and 5,000 mg/kg flour, respectively) were performed using rats. In the acute toxicity study, no toxic symptoms were observed and no rats died during the test. Body weight in the ‘Manten-Kirari’-treated group was not significantly different when compared with that of the control group. On pathologico-anatomic observation, no unusual symptoms were observed in the ‘Manten-Kirari’-treated group when compared with the control group. In the subacute toxicity study, no toxic symptoms were observed and no rats died during the test. Body weight and food intake in the ‘Manten-Kirari’-treated and common buckwheat groups were not significantly different when compared with the control group. However, some investigated properties, such as urine protein and serum albumin, were significantly different in the ‘Manten-Kirari’ and common buckwheat groups when compared with the control group. However, these changes were not caused by toxicity, but by transient changes. On pathologico-anatomic observation, some abnormalities were observed in the liver, kidneys, heart, lung, bronchi and pituitary gland in some rats. However, the incidental rates in the ’Manten-Kirari’ and common buckwheat groups did not differ when compared to controls. Therefore, these abnormalities may be caused by natural generation. Based on these results, we concluded that dough at a dose of 5,000 mg flour/kg is at a non effect level.