Chromosomal Engineering and Genomic Reconstruction of Durum Wheat: Prospects for Breeding for FHB Resistance

Allopolyploidy with multiples of divergent genomes, resulting from intergeneric hybridization in conjunction with chromosome doubling, has been a major force in plant evolution and speciation. This evolutionary pathway led to the very successful polyploid wheats, bread wheat (Triticum aestivum L., 2n = 6x = 42; AABBDD genomes) and durum wheat (Triticum turgidum L., 2n = 4x = 28; AABB genomes).  At the time of their evolution, a genetic control in the form of the Ph1 gene was established to enforce regular, diploid-like pairing and disomic inheritance. Compared to bread wheat with three genomes, durum wheat with two genomes, AA and BB, has a narrower genetic base and hence lower tolerance for added alien chromatin. We have shown, however, that despite its allotetraploid status, durum wheat is genetically buffered to the extent that it can tolerate addition of alien chromosome(s) or substitution of its chromosome(s) 1A and 1B with the corresponding chromosome 1E from a wild relative, diploid wheatgrass (Lophopyrum elongatum (Host) Á. Löve, 2n = 2x = 14; EE genome). 

The chromosome 1E is an important source of Fusarium head blight resistance.  The presence of an intact Ph1 gene confers stability to the durum disomic alien addition line and the disomic substitutions, 1E(1A) and 1E(1B).  This is an important step toward the production of scab-resistant durum cultivars.  Interestingly, chromosome 1E of the wild species compensates for the absence of durum chromosomes 1A or 1B, respectively, in its substitution lines 1E(1A) or 1E(1B), providing direct evidence of the close relationship ("genetic equivalence") between the homoeologues 1A and 1B.  The genomic reconstruction of durum wheat with wheatgrass chromatin opens up avenues for further chromosomal engineering with desirable chromosome(s) of other wild relatives. "Genetic policing" of chromosome pairing facilitates the durum genomic reconstruction.