A cytological and molecular analysis of D-genome chromosome retention following F2-F6 generations of hexaploidxtetraploid wheat crosses

Both hexaploid bread wheat (AABBDD) (Triticum aestivum L.) and tetraploid durum wheat (AABB) (T. turgidum spp. durum) are highly significant global food crops. Crossing these two wheats with different ploidy levels results in pentaploid (AABBD) F-1 lines. This study investigated the differences in the retention of D chromosomes between different hexaploidxtetraploid crosses in subsequent generations by using molecular and cytological techniques. Significant differences (P<0.05) were observed in the retention of D chromosomes in the F-2 generation depending on the parents of the original cross. One of the crosses, 2WE25x950329, retained at least one copy of each D chromosome in 48% of its F-2 lines. For this cross, the retention or elimination of D chromosomes was determined through several subsequent self-fertilised generations. Cytological analysis indicated that D chromosomes were still being eliminated at the F-5 generation, suggesting that in some hexaploidxtetraploid crosses, D chromosomes are unstable for many generations. This study provides information on the variation in D chromosome retention in different hexaploidxtetraploid wheat crosses and suggests efficient strategies for utilising D genome retention or elimination to improve bread and durum wheat, respectively.