Molecular characterization of a Thinopyrum intermedium Group 2 chromosome (2Ai-2) conferring resistance to barley yellow dwarf virus

The wheat - Thinopyrum intermedium addition lines Z1 and Z2 carry 21 pairs of wheat chromosomes and one pair of Th. intermedium chromosomes (2Ai-2) co nferring resistance to barley yellow dwarf virus (BYDV). GISH results using the genomic DNA of Pseudoroegneria strigosa (S genome) as the probe indica ted that the 2Ai-2 chromosome in Z1 and Z2 is an S-J intercalary translocat ion. Most of the 2Ai-2 chromosome belongs to the S genome, except for about one third in the middle region of the long arm that belongs to the J genom e. The results of detailed RFLP analyses confirmed that the 2Ai-2 chromosom e is extensively homoeologous to wheat group 2 chromosomes. Some new RFLP m arkers specific to the 2Ai-2 chromosome were identified. A RAPD marker, OP- R16(340), specific to the 2Ai-2 chromosome, was screened. We converted the RAPD marker into a sequence-characterized amplified region (SCAR) marker (d esignated SC-R16). The study establishes the basis for selecting translocat ion lines with small segments of the 2Ai-2 chromosome and localizing the BY DV resistance gene when introgressed into a wheat background.