Comparative telosomic mapping of homoeologous genes for brittle rachis in tetraploid and hexaploid wheats

The brittle rachis character, which causes spontaneous shattering of spikelets, is of adaptive value in wild grass species. The genes for brittle rachis were mapped using aneuploid stocks in hexaploid wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L.) The gene for brittle rachis, Br-1, from Tibetan weedraces of wheat was located on the short arm of chromosome 3D. The average distance from centromere was 20.6 cM. Br-1 did not have any effects on glume hardness. Br-2 and Br-3 from T. dicoccoides Koern. were located on the short arms of chromosome 3A and 3B, respectively. The map distance of Br-2 was 21.1 cM and that of Br-3 was 20.1 cM. It has been thought that the brittle rachis was determined by the spelt gene, q. However the present study suggests that the genes on the homoeologous group 3 chromosomes commonly determine the brittle rachis in Triticeae. In accordance with the rule for the symbolization of genes in homoeologous sets, we propose to designate the group 3 brittle rachis genes, Br-A1, Br-B1 and Br-D1.