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 thephl condition. However, recovered Gli-DllGlu-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, throughphl 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.

Fluorescence in situ hybridization (FISH) with multiple probes, consisting of highly repeated DNA sequences (pSc119.2 and pAs1) and of a low-copy, 3BS-specific RFLP sequence (PSR907), enabled determination of the physical position of the wheat-alien breakpoints (BPs) along the 3BS and 3DS arms of common wheat recombinant lines. These lines harbour 3SlS Aegilops longissima segments containing the powdery mildew resistance gene Pm13. In all 3B recombinants, the wheat-Aegilops longissima physical BPs lie within the interval separating the two most distal of the three pSc119.2 3BS sites. In all such recombinants a telomeric segment, containing the most distal of the pSc119.2 3BS sites, was in fact replaced by a homoeologous Ae. longissima segment, marked by characteristic pSc119.2 hybridization sites. Employment of the PSR907 RFLP probe as a FISH marker allowed to resolve further the critical region in the various 3B recombinant lines. Three of them, like the control common wheat, exhibited between the two most distal pSc119.2 sites a single PSR907 FISH site, which was missing in a fourth recombinant line. The amount of alien chromatin can thus be estimated to represent around 20% of the recombinant arm in the three former lines and a maximum of 27% in the latter. A similar physical length was calculated for the alien segment contained in three 3D recombinants, all characterized by the presence of the Ae. longissima pSc119.2 sites distal to the nearly telomeric pAs1 sites of normal 3DS. Comparison between the FISH-based maps and previously developed RFLP maps of the 3BS-3SlS and 3DS-3SlS arms revealed substantial differences between physical and genetic map positions of the wheat-alien BPs and of molecular markers associated with the critical chromosomal portions.Key words: wheat-alien recombinants, chromosome engineering, fluorescence in situ hybridization, highly repeated and low-copy DNA probes, physical versus genetic maps.