Breeding behavior of the cytogenetically engineered wheat-rye translocation chromosomes 1RS.1BL

The rye (Secale cereale L.) chromosome arm in the wheat-rye centric translo cation 1RS.1BL in wheat (Triticum aestivum L.) had been engineered by induc ed homoeologous recombination to remove the associated breadmaking quality defect. From a range of primary wheat-rye recombinant chromosomes, two clas ses of multipoint translocated chromosomes were assembled, MA and Te, that contain Gli-B1 and Glu-B3 loci of wheat and are missing the Sec-1 locus of rye. Their disassembly rates by recombination with normal IBS and IRS and t he segregation ratios from heterozygotes were studied in populations involv ing the original, unmodified translocation 1RS.1BL and chromosomes 1B from several wheat cultivars. Overall, the four-point translocation chromosomes MA recombined with IBS with 4.4% frequency; their intercalary rye segment r ecombined with IRS with 3.2% frequency. The overall recombination frequency of the three-point translocation chromosome Tel with IBS was 18.1% but onl y 5.4% resulted in the disassembly of the chromosome. The remaining 12.7% r ecombination was in the terminal wheat segment and in most cases it introdu ced new alleles at the wheat storage protein loci. The male transmission ra te of all engineered chromosomes was similar to that of the original 1RS.1B L translocation. In competition with IB, it was reduced to about 22 to 37%. As a result of the disassembly and reduced transmission, the probability o f selection of homozygotes for unaltered engineered chromosomes among the p rogenies of heterozygotes with IB was about 15 to 16%.