Theor Appl Genet (2009) 119:1371–1381 DOI 10.1007/s00122-009-1141-z 123 ORIGINAL PAPER Development of consistently crossable wheat genotypes for alien wheat gene transfer through Wne-mapping of the Kr1 locus Isabelle Bertin · Lesley Fish · Tracie N. Foote · Emilie Knight · John Snape · Graham Moore Received: 12 May 2009 / Accepted: 12 August 2009 / Published online: 30 August 2009  Springer-Verlag 2009 Abstract Breeders can force sexual hybridisation between wheat and related grass species to produce inter- speciWc hybrids containing a dihaploid set of wheat and related chromosomes. This facilitates the introgression of desirable genes into wheat from the secondary gene pool. However, most elite European wheat varieties carry genes that suppress crossability, making the transfer of novel traits from exotic germplasm into elite wheat varieties diY- cult or impossible. Previous studies have identiWed at least Wve crossability loci in wheat. Here, the crossability locus with the largest eVect, Kr1 on chromosome arm 5BL, was Wne-mapped by developing a series of recombinant substi- tution lines in which the genome of the normally non-cross- able wheat variety ‘Hobbit sib’ carries a recombinant 5BL chromosome arm containing segments from the crossable variety ‘Chinese Spring’. These recombinant lines were scored for their ability to cross with rye over four seasons. Analysis revealed at least two regions on 5BL aVecting crossability, including the Kr1 locus. However, the ability to set seed is highly dependent on prevailing environmental conditions. Typically, even crossable wheat lines exhibit little or no seed set when crossed with rye in winter, but show up to 90% seed set from similar crosses made in sum- mer. By recombining diVerent combinations of the two regions aVecting crossability, wheat lines that consistently exhibit up to 50% seed set, whether crossed in the UK win- ter or summer conditions, were generated, thus creating a very important tool for increasing the eYciency of alien wheat transfer programmes. Introduction The genetic diversity available within bread wheat (Triti- cum aestivum L.) is very limited compared to that of its cul- tivated relatives such as rye (Secale cereale L.), barley (Hordeum vulgare) and diploid Triticum, and within the gene pools of wild (uncultivated) grass species such as Aegilops, Triticum and Thinopyrum. It is important for wheat breeders to be able to access the genetic diversity in the secondary gene pools of wild and cultivated relatives of wheat, to develop new varieties that yield well under a wide range of adverse conditions, and that have new loci for pest and disease resistance. Many wild species, in particular, possess very good resistance to diseases and tolerance to climatic stresses such as drought and extremes of tempera- ture. However, successful exploitation of exotic germplasm in wheat breeding programmes is hindered by a number of barriers that need to be overcome to facilitate the breeding process. The Wrst barrier is the ability to generate interspe- ciWc hybrids between wheat and related species; the second is the ability to retain the chromosomes of related species in the interspeciWc hybrid zygote during embryo develop- ment; and the Wnal barrier is the ability to induce genetic exchange between the chromosomes of the two species even though these chromosomes are often divergent or Communicated by P. Langridge. Electronic supplementary material The online version of this article (doi:10.1007/s00122-009-1141-z) contains supplementary material, which is available to authorized users. I. Bertin Department of Genetics, Diversity and Ecophysiology of Cereals, UMR INRA-UBP, 234, Avenue de Brézet, 63100 Clermont-Ferrand, France L. Fish · T. N. Foote (&) · E. Knight · J. Snape · G. Moore Department of Crop Genetics, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK e-mail: tracie.foote@bbsrc.ac.uk