Supernumerary Spikelet Wheat Forms as Models for Studying Genetic Regulation of Inflorescence Development

Almost all wheat species have an unbranched spike. Tetraploid rivet wheat Triticum turgidum L., branched forms of which are widespread and have been known for about 2000 years, is an exception. As for other wheat species, supernumerary spikelet forms are rare, and supernumerary spikelet/branched spike belongs to nonstandard morphotypes. As one of the examples illustrating the law of homologous series in variation, N.I. Vavilov presented the trait "spike branching" peculiar "not only to many wheat and rye species but also to many other genera with spike inflorescence or panicle." The studies of genetic factors underlying the formation of "supernumerary spikelet/spike branching" trait and the study of peculiarities of the development of inflorescences of nonstandard branched wheat forms made it possible to demonstrate a genetic nature of hereditary variation of this trait. At the same time, the group of supernumerary spikelet/branched-lines is heterogeneous, and different genetic mechanisms can underlie the formation of branched spike. This review presents a retrospective of scientific studies devoted to the creation of supernumerary spikelet wheat forms and to the study of genetics of "supernumerary spikelet/spike branching" trait and demonstrates the results of modern studies of genetic regulation of morphogenesis of cereal inflorescences using supernumerary spikelet lines as genetic models.