Wheat chromosome engineering at the 4x level: The potential of different alien gene transfers into durum wheat

With the aim of making the point on feasibility and relative success of alien transfers into durum wheat via chromosome engineering, three transfer works, differing in origin and content of the alien introduction and in the transfer strategy adopted, are described. For the transfer of a powdery mildew resistance gene, Pm13, originating from Aegilops longissima and previously transferred to common wheat chromosome 3B, as well as for that of the leaf rust resistance gene Lr19 and its associated Yp (yellow pigment) gene, deriving from Ag. elongatum and introduced into 7A, the common wheat recombinants were employed as donors, from which the alien segments were homologously transferred into durum genotypes. On the other hand, for the transfer of common wheat chromosome 1D seed storage protein genes, phl mediated homoeologous recombination was repeatedly induced. This resulted in loss of individuals, including potentially desirable recombinants, probably due to imbalances created by the phl condition. However, recovered Gli-D1/Glu-D3 tetraploid recombinants exhibited normal transmission and fertility. Preliminary evidence indicates a normal behaviour also for Glu-D1 '5 + 10' putative recombinants. Similarly, there was no negative impact from the transfer of the Pm13 gene, which has been successfully pyramided into Pm4a durum varieties. On the contrary, transfer of the Ag. elongatum segment showed normal female but almost no male transmission in one durum genotype. This in spite of the fact that the alien segment, proved to be, through in situ hybridization, considerably longer than previously believed, should contain an Sd-1 gene, causing preferential transmission in common wheat. While its behaviour is being checked in other durum genotypes, shortening of the alien segment, through ph1 induced recombination, is also being carried out. Possible causes of the severe negative selection that this alien transfer seemingly encounters at the tetraploid level are discussed.