The third glume phenotype is associated with rachilla branching in the spikes of tetraploid wheat (Triticum L.)

We investigated the new inflorescence architectural character “three glumes” and a new status of ramification in tetraploid wheat. Using 9 tetraploid accessions with “turgidum type of branching”, the segregation of branched spike and the third glume indicated the complete linkage of genes for both phenotypes. The rachilla were elongated and bore florets at basal nodes while bearing spikelets at the apical nodes in T. durum Desf. TRI 9644 and T. turgidum L. PI 67339. The phenotype was different from “sham-ramification” in Triticum jakubzineri Udacz. et Schachm., with florets at basal and apical nodes of elongated spikelet rachilla. We confirmed a new status of ramification, “false-true ramification”. It was considered that the “false-true ramification” was determined by the shr2 gene in the long arm of chromosome 2A because the ramification of PI 67339 and TRI 9644 was supposed to be allelic. The segregation of “sham-ramification” and the third glume also indicated the complete linkage of genes for both phenotypes. Thus we concluded that the presence of third glume phenotype is associated with rachis and rachilla branching in the spikes of tetraploid wheat. The present study confirmed the existence of three distinct types of spike ramification, whose classification is not entirely unified: (a) “true ramification”—“branched spike”—“genuine branching”—“turgidum type of branching”, (b) “false ramification”—“pseudo-branched spike”—“sham ramification”—“vavilovii type of branching” and (c) “false-true ramification”.