Identification and characterization of wheat-wheatgrass translocation lines and localization of barley yellow dwarf virus resistance

Stable introgression of agronomically important traits into crop plants thr ough wide crossing often requires the generation and identification of tran slocation lines. However, the low efficiency of identifying lines containin g translocations is a significant limitation in utilizing valuable alien ch romatin-derived traits. Selection of putative wheatgrass-wheat translocatio n lines based on segregation ratios of progeny from gamma-irradiated seed u sing a standard phenotypic analysis resulted in a low 4% success rate of id entifying barley yellow dwarf virus (BYDV) resistant and susceptible transl ocation lines. However, 58% of the susceptible progeny of this irradiated s eed contained a Thinopyrum intermedium chromosome-specific repetitive seque nce, which indicated that gamma-irradiation-induced translocations occurred at high rate. Restriction fragment length polymorphism (RFLP) analysis of susceptible lines containing alien chromatin, their resistant sister lines and other resistant lines showed that more than one third of the progeny of gamma-irradiated double monosomic seeds contained wheatgrass-wheat translo cations. Genomic in situ hybridization (GISH) analysis of selected lines co nfirmed that these were wheatgrass-wheat translocation lines. This approach of initially identifying BYDV susceptible deletion lines using an alien ch romosome-specific repetitive sequence followed by RFLP analysis of their re sistant sister lines efficiently identified resistant translocation lines a nd localized the BYDV resistance to the distal end of the introgressed Th. intermedium chromosome.