Theor Appl Genet (1990) 80:609-616 9 Springer-Verlag 1990 Linkage mapping of genes for resistance to leaf, stem and stripe rusts and m-secalins on the short arm of rye chromosome 1R N.K. Singh 1, ,, K.W. Shepherd 1 and R.A. MeIntosh 2 1 The University of Adelaide, Agronomy Department, Waite Agricultural Research Institute, Glen Osmond, S.A. 5064, Australia 2 The University of Sydney, Plant Breeding Institute, P.O. Box 180, Castle Hill, N.S.W. 2154, Australia Received April 24, 1990; Accepted June 1, 1990 Communicated by E Salamini Summary. The genes controlling resistance to three wheat rusts, viz., leaf rust (Lr26), stem rust (St31) and stripe or yellow rust (Yr9), and co-secalins (Secl), located on the short arm of rye chromosome IR, were mapped with respect to each other and the centromere. Analysis of 214 seeds (or families derived from them) from test- crosses between a IBL.IRS/IR heterozygote and 'Chi- nese Spring' ditelocentric 1BL showed no recombination between the genes for resistance to the three rusts, sug- gesting very tight linkage or perhaps a single complex locus conferring resistance to the three rusts. The rust resistance genes were located 5.4_+ 1.7 cM from the Secl locus, which in turn was located 26.1 _+ 4.3 cM from the centromere; the gene order being centromere - Seel - Lr26/Sr31/Yr9 telomere. In a second test-cross, using a different IBL.1RS translocation which had only stem rust resistance (SrR), the above gene order was con- firmed despite a very large proportion of aneuploids (45.8%) among the progeny. Furthermore, a map dis- tance of 16.0 + 4.8 cM was estimated for SrR and the telomeric heterochromatin (C-band) on I RS. These re- sults suggest that a very small segment of 1RS chromatin is required to maintain resistance to all three wheat rusts. It should be possible but difficult to separate the rust resistance genes from the secalin gene(s), which are thought to contribute to dough stickiness of wheat-rye translocation lines carrying 1RS. Key words: Rye - Secalins Rust resistance Stem rust Leaf rust - Stripe/yellow rust - Linkage mapping * To whom correspondence should be addressed Introduction The short arm of chromosome IR of cereal rye (Secale cereale) carries a number of genes of agronomic impor- tance, and when transferred to wheat in the form of IBL.1RS and 1AL.1RS translocations has resulted in some valuable new cultivars. For example, the highly successful 'Veery' lines developed at CIMMYT (Rajaram et al. 1983) were derived from cv 'Kavkaz', which carries chromosome arm 1RS from 'Petkus' rye as a 1BL.1RS translocation (Mettin et al. 1973; Zeller /973). This rye arm carries genes conferring resistance to leaf, stem and stripe rusts and powdery mildew, described as Lr26, Sr31, Yr9 and Pm8, respectively (McIntosh 1988), but the exact location and linkage relationships of these genes is not known. Another wheat, cv 'Amigo', possess- es a 1AL.IRS translocation, and the rye arm in this line is thought to be responsible for the resistance of this cultivar to greenbug (Schizaphis graminum), powdery mildew and stem rust (Wood et al. 1974; Lowry et al. 1981; Zeller and Fuchs 1983). Due to their disease and pest resistance and high yielding potential, these translo- cation lines have been used widely in breeding programs around the world, and many cultivars have been re- leased. However, in contrast to their desirable agronomic traits, wheats carrying these translocations generally pro- duce a flour with serious quality defects (Zeller et al. 1982; Dhaliwal et al. 1987). In particular, doughs derived from them often show marked stickiness, reduced dough strength and intolerance to overmixing, and this has seri- ously limited their use in those countries where leavened bread is the main end-product of the flour. Some other translocation lines involving IRS of 'Im- perial' rye have also been isolated, including a ]AL.IRS translocation in 'Chinese Spring' (CS) wheat background (Singh and Shepherd 1988 b), a 1BL. 1RS translocation in