The Ph gene and the origin of tetraploid wheats

None of the diploid species of Triticum and Aegilops, from which tetraploid emmer and timopheevii wheats were presumably derived, presently possess a Ph gene identical to that on the long arm of chromosome 5B of T. aestivum. This suggests that the Ph gene originated at the tetraploid level. Both emmer and Timopheevii completely compensate for the absence of chromosome 5B of T. aestivum clearly due to the presence of a Ph gene identical to that on chromosome 5B. The presence of a similar Ph gene in both the tetraploids and its absence in the putative diploid parents suggests that the tetraploids diverged from a common amphiploid ancestor after the origin of the Ph gene. The possibility of independent origin of the tetraploids involving an unidentified common B genome donor with the Ph gene at the diploid level, however, can not be completely ruled out.