The major threshability genes soft glume (sog) and tenacious glume (Tg), of diploid and polyploid wheat, trace their origin to independent mutations at non-orthologous loci

Threshability is an important crop domestication trait. The wild wheat progenitors have tough glumes enveloping the floret that make spikes difficult to thresh, whereas cultivated wheats have soft glumes and are free-threshing. In hexaploid wheat, the glume tenacity gene Tg along with the major domestication locus Q control threshability. The Q gene was isolated recently and found to be a member of the AP2 class of transcription factors. However, only a few studies have reported on the tough glume trait. Here, we report comparative mapping of the soft glume (sog) gene of diploid Triticum monococcum L. and tenacious glume (Tg) gene of hexaploid T. aestivum L. using chromosome-specific SSR and RFLP markers. The sog gene was flanked by Xgwm71 and Xbcd120 in a 6.8 cM interval on chromosome 2A(m)S of T. monococcum whereas Tg was targeted to a 8.1 cM interval flanked by Xwmc503 and Xfba88 on chromosome 2DS of T. aestivum. Deletion bin mapping of the flanking markers assigned sog close to the centromere on 2AS, whereas Tg was mapped to the most distal region on 2DS. Both 2AS and 2DS maps were colinear ruling out the role of chromosome rearrangements for their non-syntenic positions. Therefore, sog and Tg are not true orthologues suggesting the possibility of a diverse origin.