Molecular cytogenetic identification of a wheat-Thinopyrum ponticum translocation line resistant to powdery mildew

Thinopyrum ponticum (2n = 70) serves as a valuable gene pool for wheat improvement. Line SN0224, derived from crosses between Th. ponticum and the common wheat cultivar Yannong15, was identified in the present study. Cytogenetic observations showed that SN0224 contains 42 chromosomes in the root-tip cells and 21 bivalents in the pollen mother cells, thereby demonstrating its cytogenetic stability. Genomic in situ hybridization, probed with the total genomic DNA of Th. ponticum, produced hybridization signals in the distal region of two wheat chromosome arms. After inoculation with the Blumeria graminis f. sp. tritici (Bgt) isolates, SN0224 exhibited immunity. Segregation in F1s and F2s from the cross SN0224/cv. Huixianhong indicated that SN0224 carries a single dominant gene for powdery mildew (Pm) resistance, which was temporarily designated PmSn0224. Three markers Barc212, Xwmc522 and Xbarc1138 were detected to be linked with PmSn0224. Based on the locations of the markers, PmSn0224 was located on the chromosome 2A. None of the three markers above is linked with the previously reported PM resistance genes on chromosome 2A, and none of the previously reported PM resistance genes on chromosome 2A is related to Th. ponticum. Therefore, PmSn0224 is likely a novel gene putatively from Th. ponticum.