Polyploid origin of Eragrostis tef: evidence from the waxy locus

Eragrostis tef (Zucc.) Trotter (Poaceae) is an allotetraploid cereal crop cultivated primarily in Ethiopia and Eritrea. Of the approximately 350 species in Eragrostis, a total of thirteen potential diploid and polyploid progenitors have been proposed to be the sources of tef's genome, but rigorous tests of these competing hypotheses have not been performed. We are using sequence data from a 1250 bp region of the waxy locus (granule-bound starch synthase; GBSSI), a low-copy nuclear gene, to test the hypotheses of tef's origins. We have amplified 2 partial and 4 complete exons and 5 introns from this locus, and have sampled homoeologous copies of the gene in the polyploid taxa. Preliminary results from cladistic analyses of waxy sequences support the widely held notion that tef is a domesticate of E. pilosa, a widespread and morphologically similar allotetraploid.