Tomoyuki Katsube-Tanaka

Common buckwheat, Fagopyrum esculentum, is an orphan crop domesticated in southwest China that exhibits heterostylous self-incompatibility. Here we present chromosome-scale assemblies of a self-compatible F. esculentum accession and a self-compatible wild relative, Fagopyrum homotropicum, together with the resequencing of 104 wild and cultivated F. esculentum accessions. Using these genomic data, we report the roles of transposable elements and whole-genome duplications in the evolution of Fagopyrum. In addition, we show that (1) the breakdown of heterostyly occurs through the disruption of a hemizygous gene jointly regulating the style length and female compatibility and (2) southeast Tibet was involved in common buckwheat domestication. Moreover, we obtained mutants conferring the waxy phenotype for the first time in buckwheat. These findings demonstrate the utility of our F. esculentum assembly as a reference genome and promise to accelerate buckwheat research and breeding.

Green stem disorder (GSD) is an important agronomical problem in soybean production because it delays leaf and stem senescence and complicates the harvest. However, a rapid and precise diagnosis of GSD has not yet been established. In this study, the effect of depodding on GSD and vegetative storage protein (VSP) accumulation was investigated in GSD-susceptible cultivar ‘Tachinagaha (Tc)’ and GSD-resistant experimental line ‘Touhoku 129 (Th)’ under two different (early and late) sowing dates in 2020 and 2021. Intact Tc plants showed relatively severe GSD at early sowing in 2020 and late sowing in 2021, whereas intact Th plants showed little GSD at both sowing dates and in both years. Meanwhile, depodding reproducibly induced GSD and increased stem weight for both Tc and Th. The relative VSP content peaked 14–21 days after R3 (DAR3) in intact plants and increased afterward in depodded plants. The relative VSP content differed at 28 DAR3 between intact and depodded plants, which was earlier than the timing when SPAD (soil plant analysis development) values differed, suggesting that VSP accumulation might be a better indicator of GSD than the SPAD value. The present study will contribute to the development of tools for diagnosing GSD. GRAPHICAL ABSTRACT

Green stem disorder (GSD), characterized by delayed stem senescence during seed maturation, complicates harvesting in soybean production. Although GSD is associated with a sink – source imbalance, a rapid and precise evaluation of GSD has not been established. In sink-limited soybean plants, vegetative storage protein (VSP) accumulates. In this study, pot and field experiments were conducted to reevaluate the relationship between GSD, sink – source imbalance caused by soil moisture change, and VSP accumulation as a possible indicator of GSD in Kyoto, Japan over two years. Drought treatment for four weeks from R1 (beginning flowering), R3 (beginning pod), or R5 (beginning seed) growth stage in pots using the short growth-period cultivar Yukihomare reduced sink size in both years, but reduced relative sink mass (pod weight/shoot weight) and increased GSD severity only in 2017, suggesting that sink-source imbalance, affected by soil moisture, can induce GSD. Soil moisture change from around R3 or R5 to maturity in fields using trench-filled or unfilled water tended to change GSD severity but not VSP accumulation in the uppermost fully expanded leaves from R5 (2018) or 15 days before R5 (2019) to 28 days after R5. GSD and VSP responses, however, differed between the two contrasting cultivars, Tachinagaha and Touhoku 129, suggesting the potential usability of VSP for GSD evaluation. GRAPHICAL ABSTRACT