Bread wheat originated from the hybridization of three different wild progenitor species. These progenitors are genetically diverse and have been the source of many economically important genes for cultivated wheat improvement, especially with respect to disease resistance.
In the recent paper by Scott et al. (2014), 1,320 accessions of 10 different species of Aegilops from Israel were evaluated for their reaction to widely virulent pathotypes of the stem rust pathogen from Africa (i.e. pathotypes in the Ug99 lineage such as TTKSK). Aeg. longissima and Aeg. speltoides had the highest frequency of resistance (97-100%) to pathotype TTKSK, followed by Aeg. bicornis (79%) and Aeg. sharonensis (77%). Overall, 346 Aegilops accessions were resistant to the three virulent African stem rust pathotypes of TTKSK, TTKST, and TTTSK. Thus, there is great potential for identifying new stem rust resistance genes that can be used in wheat.
Although very cumbersome, it is feasible to transfer genes from Aegilops into wheat through various wide-crossing schemes. However, there are many problems to address including the timing of flowering and dehiscence, low hybrid seed set, reduced chromosome pairing and segment exchange, and the presence of antigameticidal genes in some Aegilops species. In a recent paper by Millet et al. (2014), a comprehensive procedure was used to overcome some of these major obstacles, leading to the successful transfer of leaf rust and stripe rust resistance from Aeg. sharonensis (Sharon goatgrass) into wheat. This was done by inducing homoeologous recombination by the ph1b allele to obtain resistant wheat recombinant lines carrying the alien chromosome segments in the genetic background of the spring wheat cultivar Galil. Gametocidal genes in Aeg. sharonensis can complicate the transfer of genes into wheat. This obstacle was overcome by using an “antigametocidal” wheat mutant. The resistant recombinant wheat lines produced in this study will be useful in programs breeding wheat for resistance to leaf and stripe rust.
Brian Steffenson is the Lieberman-Okinow Endowed Chair of Cereal Disease Resistance at the University of Minnesota