The Q locus of Iranian and European spelt wheat

A dominant allele at the Q locus on chromosome 5A is believed to be the pri ncipal factor responsible for free-threshing, square-head spikes with a non fragile rachis in bread wheat, Triticum aestivum ssp. aestivum. The spelt s yndrome, resulting in pyramidal spikes with a brittle rachis and hulled gra in in I: aestivum, is believed to be principally caused by the q allele. Ch romosome 5A of European and Iranian spelt was substituted for 5A of bread w heat and the lines were characterized with molecular markers. The substitut ion of bread wheat chromosome 5A by 5A of European spelt resulted in weakly hulled, pyramidal spikes with a non-brittle rachis, whereas and the substi tution of 5A by 5A of Iranian spelt did not alter spike morphology at all. It is concluded that the expression of the spelt syndrome depends, to a lar ge extent, on the interactions of q with genes controlling glume tenacity a nd rachis fragility on other chromosomes. The genetic basis for the spelt s yndrome and the apparent presence of the Q allele in Iranian spelt are disc ussed.