PHYSICAL MAPPING OF TRANSLOCATION BREAKPOINTS IN A SET OF WHEAT-AEGILOPS UMBELLULATA RECOMBINANT LINES USING IN-SITU HYBRIDIZATION

Aegilops umbellulata Zhuk. carries genes at Glu-U1 loci that code for a pair of high-melecular-weight glutenin subunits not found in common wheat, Triticum aestivum. Wheat-Ae. umbellulata recombinant lines were produced with the aim of transferring genes coding for glutenin subun its from Ae. umbellulata into wheat with minimal flanking material. We used fluorescent genomic in situ hybridization to evaluate the extent of recombination and to map physically the translocation breakpoints on 11 wheat-Ae. umbellulata recombinant lines. In situ hybridization w as able to identify alien material in wheat and showed breakpoints not only near the centromeres but also along chromosome arms. To characte rize and identify chromosomes further, including deletions along the 1 U chromosome, we used simultaneous multiple target in situ hybridizati on to localize a tandemly repeated DNA sequence (pSc119.2) and the 18S -25S and 5S rRNA genes. One line contained an Ae. umbellulata telocent ric chromosome and another two had different terminal deletions, mostl y with some wheat chromosome rearrangements. Although from six indepen dent original crosses, the other eight lines included only two types o f intercalary wheat Ae. umbellulata recombination events. Five occurre d at the 5S rRNA genes on the short arm of the pie. umbellulata chromo some with a distal wheat-origin segment, and three breakpoints were pr oximal to the centromere in the long arm, so most of the long arm was of Ae. umbellulata origin. The results allow characterization of recom bination events in the context of the karyotype. They also facilitate the design of crossing programmes to generate lines where smaller Ae. umbellulata chromosome segments are transferred to wheat, with the pot ential to improve bread-making quality by incorporating novel glutenin subunits without undesirable linked genes.