Ph-I-induced transfer of leaf and stripe rust-resistance genes from Aegilops triuncialis and Ae. geniculata to bread wheat

Leaf and stripe rusts are severe foliar diseases of bread wheat. Recently, chromosomes 5M(g) from the related species Aegilops geniculata that confers resistance to both leaf and stripe rust and 5U(t) from Ae. triuncialis conferring resistance to leaf rust have been transferred to bread wheat in the form of disomic DS5M(g) (5D) and DS5U(t) (5A) chromosome substitution lines. The objective of this study was to shorten the alien segments in these lines using Ph-I-mediated, induced homoeologous recombination. Putative recombinants were evaluated for their rust resistance, and by genomic in situ hybridization and microsatellite analyses. One agronomically useful wheat-Ae. geniculata recombinant resistant to leaf and stripe rust was identified that had only a small terminal segment of the 5M(g) L arm transferred to the long arm of an unidentified wheat chromosome. This germplasm can be used directly in breeding programs. Only one leaf rust-resistant wheat-Ae. triuncialis recombinant, which consists of most of the complete 5U(t) chromosome with a small terminal segment derived from 5AS, was identified. This germplasm will need further chromosome engineering before it can be used in wheat improvement.