Physical mapping of chromosome 4J of Thinopyrum bessarabicum using gamma radiation-induced aberrations

Gamma radiation induced a series of structural aberrations involving Thinopyrum bessarabicum chromosome 4J. The aberrations allowed for deletion mapping of 101 4J-specific markers and fine mapping of blue-grained gene BaThb. Irradiation can induce translocations and deletions to assist physically locating genes and markers on chromosomes. In this study, a 12-Gy dosage of (60)Co-γ was applied to pollen and eggs of a wheat (Triticum aestivum) landrace Chinese Spring (CS)-Thinopyrum bessarabicum chromosome 4J disomic addition line (DA4J), and the gametes from irradiated plants were fertilized with normal CS eggs or pollen to produce M1 seeds. Based on genomic in situ hybridization analysis of 261 M1 plants, we identified 74 lines carrying structural aberrations involving chromosome 4J with the higher aberration rate in treated pollen (31.2 %) than in the treated eggs (21.3 %). We further identified 43 (53.8 %) lines with structural aberrations on chromosome 4J by analyzing another 80 M1 plants with 74 4J-specific markers, indicating that combining molecular and cytological methods was more efficient for detecting chromosome aberrations. Marker analysis thus was performed prior to cytogenetic identification on M2-M4 seeds to detect chromosome structural aberrations. Sixty-eight M3 lines with structural aberrations on chromosome 4J and six previously obtained chromosome 4J alien lines were then analyzed using 101 chromosome 4J-specific markers. After combining marker results with chromosome aberrations in each line, chromosome 4J was physically divided into 24 segmental blocks with 7 in the short arm and 17 in the long arm. The blue-grained gene BaThb was further mapped into the region corresponding to block 4JL-11. The chromosome aberrations and the physical map developed in this research provide useful stocks and tools for introgression of genes on chromosome 4J into wheat.