The vulgare super gene, Q: its universality in durum wheat and its phenotypic effects in tetraploid and hexaploid wheats

Abstract

The genotype at the Q locus on chromosome 5A of Triticum durum Desf. (2n = 28, AABB), a species with keeled glumes and tough rachis, was studied by either crossing the species with, or substituting its 5A into, a hexaploid common wheat, T. aestivum (L.)Thell. ssp. vulgare (Vill.) MK. cv. Chinese Spring (2n = 42, AABBDD, QQ genotype). Contrary to the opinion of previous researchers that keeled-glumed wheats always have the spelta gene, q, the durum strains studied had a hypermorphic allele, the vulgare gene, Q. No speltoid plants appeared in the progeny of the crosses, and disomic substitution lines (2n = 2) had squareheaded (= vulgare type) spikes. Also, three doses of the long arm of 5A of durum produced compactoidy. Apparently, Q does not produce round glumes in the genetic backgrounds of most tetraploids except T. carthlicum Nevski. The phenotype conditioned by Q, which is evidently present in all free-threshing tetraploid wheats, is somewhat different at the tetraploid level from that in hexaploids. The presence of Q tends to magnify the differences in the degree of expression of certain minor characters.Key words: Triticum, phylogeny, vulgare gene, pleiotropic gene, dosage effect, interaction.