Molecular cytogenetic characteristics of a translocation line between common wheat and Thinopyrum intermedium with resistance to powdery mildew

Powdery mildew caused by Blumeria graminis (DC) Speer f. sp. tritici Em. Marchal is a serious disease of wheat (Triticum aestivum L.) in Southwestern China. A line of common wheat designated 08-723 isolated from the progeny of a hybrid between common wheat and Thinopyrum intermedium (Host) Barkworth & Dewey, was highly resistant to the existing powdery mildew races in the region. This line had a similar phenotype to its wheat parent, and it showed normal bivalent pairing at metaphase I of meiosis. It was analyzed by genomic in situ hybridization, fluorescence in situ hybridization and sequential C-banding-GISH to determine the amount, location and origin of the alien chromatin present. The results revealed that line 08-723 is homozygous for a two-point translocation replacing chromosome 6A of wheat. The translocation chromosome appears to have a normal 6AL arm; its short arm has a short terminal segment of ca. 10 % in length originating from an unidentified B-genome chromosome of wheat and a long proximal segment of ca. 90 % of the arms' length originating from one of the St-genome chromosomes of Th. intermedium. Genetic analysis of powdery mildew resistance in F-1, F-2 and F-2:3 populations from a cross of 08-723 with a susceptible wheat line indicated that the resistance was controlled by a single dominant gene and in a sample of F2 plants it always associated with the translocated chromosome. The gene responsible for resistance on the translocated chromosome may provide an alternate source of resistance in wheat breeding programs.