RESUMEN
Compared to common buckwheat (F. esculentum), Tartary buckwheat (F. tataricum) is very polymorphic in the type of seeds, but a seed type which is typical for F. esculentum, i.e. triangular seeds with flat sides and clear ribs, has been not found among the polymorphism. However, such seed type is typical for wild species F. cymosum which produces fertile hybrids in crosses with F. tataricum. Embryo rescue based interspecific cross F. esculentum × F. cymosum allowed reveal functional allelism of the genes determining the similar morphs of these species' seeds, i.e. the seed type resulted from mutation(s) at same gene. The gene can be assigned as TAN (triangular). Variation for the seed shell thickness among recessives for the TAN carrying about 12% of F. tataricum genome, together with the shell thickness of a seed from the F1 hybrid F. esculentum × F. cymosum compared to ones of the parents, suggests there are some genes influencing seed shell thickness. Also, it was supported by analyses of seeds characteristics of Tartary-based forms with some share of F. cymosum genetic material. In addition, cross F. tataricum × F. cymosum looks like an effective tool to increase 1000-seed weight of Tartary buckwheat-based breeding material.
RESUMEN
Introduction: Understanding the complex inflorescence architecture and developmental morphology of common buckwheat (Fagopyrum esculentum) is crucial for crop yield. However, most published descriptions of early flower and inflorescence development in Polygonaceae are based on light microscopy and often documented by line drawings. In Fagopyrum and many other Polygonaceae, an important inflorescence module is the thyrse, in which the primary axis never terminates in a flower and lateral cymes (monochasia) produce successively developing flowers of several orders. Each flower of a cyme is enclosed together with the next-order flower by a bilobed sheathing bract-like structure of controversial morphological nature. Methods: We explored patterns of flower structure and arrangement in buckwheat and its wild relatives, using comparative morphology, scanning electron microscopy and X-ray microtomography. Results: Our data support interpretation of the sheathing bract as two congenitally fused phyllomes (prophylls), one of which subtends a next-order flower. In tepal-like bract, a homeotic mutant of F. esculentum, the bilobed sheathing bract-like organ acquires tepal-like features and is sometimes replaced by two distinct phyllomes. Wild representatives of F. esculentum (ssp. ancestrale) and most cultivars of common buckwheat possess an indeterminate growth type with lateral thyrses produced successively on the primary inflorescence axis until cessation of growth. In contrast, determinate cultivars of F. esculentum develop a terminal thyrse after producing lateral thyrses. In contrast to F. esculentum, the occurrence of a terminal thyrse does not guarantee a determinate growth pattern in F. tataricum. The number of lateral thyrses produced before the terminal thyrse on the main axis of F. tataricum varies from zero to c. 19. Discussion: The nine stages of early flower development formally recognized here and our outline of basic terminology will facilitate more standardized and readily comparable descriptions in subsequent research on buckwheat biology. Non-trivial relative arrangements of tepals and bracteoles in Fagopyrum and some other Polygonaceae require investigation using refined approaches to mathematical modelling of flower development. Our data on inflorescence morphology and development suggest contrasting evolutionary patterns in the two main cultivated species of buckwheat, F. esculentum and F. tataricum. The genus Fagopyrum offers an excellent opportunity for evo-devo studies related to inflorescence architecture.