The International Maize and Wheat Improvement Center (CIMMYT) acts as a catalyst and leader in a global maize and wheat innovation network that serves the poor in the developing world. Drawing on strong science and effective partnerships, CIMMYT researchers create, share, and use knowledge and technology to increase food security, improve the productivity and profitability of farming systems and sustain natural resources. This peoplecentered mission does not ignore the fact that CIMMYT's unique niche is as a genetic resources enhancement center for the developing world, as shown by this review article focusing on wheat.

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Aegilops species have significantly contributed to wheat breeding despite the difficulties involved in the handling of wild species, such as crossability and incompatibility. A number of biotic resistance genes have been identified and incorporated into wheat varieties from Aegilops species, and this genus is also contributing toward improvement of complex traits such as yield and abiotic tolerance for drought and heat. The D genome diploid species of Aegilops tauschii has been utilized most often in wheat breeding programs. Other Aegilops species are more difficult to utilize in the breeding because of lower meiotic recombination frequencies; generally they can be utilized only after extensive and time-consuming procedures in the form of translocation/introgression lines. After the emergence of Ug99 stem rust and wheat blast threats, Aegilops species gathered more attention as a form of new resistance sources. This article aims to update recent progress on Aegilops species, as well as to cover new topics around their use in wheat breeding.

To date, the International Maize and Wheat Improvement Center (CIMMYT) has produced more than 1000 synthetic hexaploid wheats (SHWs), using diverse accessions of the D genome donor species (Aegilops tauschii). Many of these SHWs produced from many different Ae. tauschii have shown resistance or tolerance to various biotic and abiotic stresses, indicating the potential importance of the Ae. tauschii gene pool for breeding purposes. SHWs were backcrossed to CIMMYT improved germplasm to produce synthetic backcross-derived lines (SBLs), which are agronomically similar to the improved parents, but retain the introgressed traits of interest under selection and thereby new diversity. Molecular studies show that SHWs and SBLs are genetically diverse at the DNA level when compared with traditional bread wheat cultivars and preferential transmission of some alleles from the SHW parent has been seen in all genomes, indicating positive selection. Marker analyses of wheat cultivars released over time indicate that SBLs are ideal materials to simultaneously increase yield and diversity for other traits. Following successful diversification of the wheat D genome, CIMMYT has shifted to target improvement of hexaploid wheat via the A and B genomes, focusing on specific traits. Screening the CIMMYT germplasm collection of T. turgidum subsp. dicoccum for Russian wheat aphid resistance and drought tolerance revealed varying levels of phenotypic expression. Promising accessions will be used for the production of new SHWs for future introgressions into elite bread wheat backgrounds.