THE GENETICS OF RACHIS FRAGILITY AND GLUME TENACITY IN SEMIWILD WHEAT

The inheritance of rachis fragility and glume tenacity in semi-wild wh eat was studied in an attempt to help establish the taxonomic status a nd genetic origin of semi-wild wheat. Progenies of crosses and backcro sses of semiwild wheat with the cultivar Columbus (common wheat) indic ated that the fragile rachis and non-free-threshing character of semi- wild wheat were dominant to the tough rachis and free-threshing charac ter of common wheat. F-2 and backcross data indicated that the rachis fragility and glume tenacity of semi-wild wheat were each controlled b y a single gene in the cross of semi-wild wheat with Columbus. In the cross of semi-wild wheat with Triticum aestivum spp. spelta, the F-2 a nd F-3 population did not segregate for glume tenacity, but did segreg ate for rachis fragility. The F-2 and backcross data suggest that thre e genes interact to control three types of rachis fragility, i.e. semi -wild wheat-type, spelta-type and the tough rachis of common wheat. Se mi-wild wheat differs from common wheat in rachis fragility and glume tenacity. This wheat also differs from other wheats with fragile rachi s and tenacious glumes (T. aestivum ssp. spelta, macha and vavilovii) in the pattern and degree of rachis disarticulation. We conclude that semi-wild wheat is likely a subspecies within T. aestivum at the same taxonomic level as spp. spelta, macha and vavilovii.