A genetransfer strategy based on durum wheat–Aegilops comosa amphiploid top-crossed with hexaploid wheat results in elimination of D chromosomes led to the production of homoeologous M(D) substitutions and translocations

Abstract

Background Domestication and nearly eight thousand years of cultivation have resulted in a narrow genetic base, which hinders the identification of effective allele combinations and hampers breeding progress under changing environmental conditions. The gene portfolio can be extended using a crossing strategy providing favourable conditions for the formation of wheat × alien chromosome addition, substitution and translocation lines. To utilize the gene pool of Aegilops comosa, the present study applied durum wheat–Ae. comosa amphiploids top-crossed (TC) by hexaploid wheat (Mv9kr1ph1b), a strategy exploiting monosomic conditions of D- and M-genomes in TC1 to form cytogenetic stocks. Results While the expected genome structure of amphiploid and TC1 generations was confirmed, consecutive in situ hybridization using D- and M-genomic, as well as DNA repeat probes on 52 TC2F1 lines, showed significant elimination of not only M- but also D-genome chromosomes. Differences in the elimination frequency seemed to be related to chromosome size, with an opposite tendency for the two genomes, as shorter M chromosomes (1M,4M, 6M) were retained more frequently, while the shorter D chromosomes (1D, 4D) were predominantly eliminated. D–M rearrangements within group 1, 3, 4, and 6 chromosomes were dominantly homoeologous, with 5D/5M recombinations observed at the highest frequency. Besides monosomic introgressions, disomic substitutions 2M(2D) and 7M(7D), addition 6M, and translocation T6MS·6ML-6D were selected. Morphological characterization and yield components indicated the good compensation ability of these Ae. comosa chromosomes for the loss of those of wheat.
Conclusions Relationships between chromosomes size and their elimination from wheat × alien hybrid progenies were discussed. Based on the high level of homoeologous recombinations and substitutions, top-crossing has proven to be an effective strategy for transferring alien chromosome segments from closely related diploid species into wheat. The newly developed wheat–Ae. comosa prebreeding materials represent potentially valuable genetic resources for wheat improvement.