Insights into Homoeologous Recombination Between Wild- and Cultivated Wheat

Hexaploid wheat is an allopolyploid, containing three closely related A, B and D genomes, but behaves as a diploid at meiosis. Ph1 is a locus with a major effect on homologous pairing, which evolved during the polyploidization events that led to the establishment of the species. In the absence of Ph1, homoeologous recombination occurs between homoeologous wheat chromosomes and alien chromosomes. Thus, the mutant (ph1b) has been used for directed transfer of alien chromatins to wheat chromosomes. Here we present another approach to induce homoeologous recombination between the wild and cultivated wheat chromosomes in presence of normal Ph1. The ovate goat grass Aegilops geniculata Roth (U^gU^gM^gM^g) is an excellent source of resistance genes against various pests and diseases and has been used in the past for genes transfers to wheat using ph1b-induced homoeologous recombination. Meiotic pairing analysis of F₁ hybrid between TA6675 [a disomic substitution line DS5M (5D) which has 5M from Ae. geniculata (TA10437)] in the wheat cultivar, Chinese Spring revealed the presence of multivalent formation. GISH analysis in derived progenies confirmed presence of several spontaneous recombinants, providing evidence that homoeologous recombination between wheat chromosome 5D and Ae. geniculata chromosome 5M occurs in presence of Ph1. The possible mechanisms will be presented.