USA The free-threshing habit in wheat has been extensively investigated because of both its evolutionary significance and its practical importance in breeding programs. Several genetic systems that govern threshability have been reported.
Some studies suggest polygenic inheritance while others have identified major genes.
A major gene or complex, the Q factor, located on the long arm of chromosome 5A affects rachis fragility and glume brittleness as well as spike morphology. Another partially dominant gene in synthetic hexaploids, Tg , on chromosome 2D derived from Aegilops tauschii , inhibits the expression of Q . This study was conducted to identify and locate quantitative trait loci affecting free-threshing habit and spike morphology in the ITMI recombinant inbred line mapping population. RILs were evaluated for threshability and spike morphology characters. DNA-based marker saturation of putative QTLs is underway.