Molecular Mapping Of Stripe Rust Resistance Gene YrCH42 In Wheat Cultivar Chuanmai 42 And Its Allelism With Yr24 And Yr26

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases on wheat in the world. It is an effective way to use resistant cultivars to control the disease. Marker-assisted selection can certainly accelerate the development of resistant wheat cultivars in pyramiding resistance genes and breeding multi-line cultivars. Chuanmai 42, derived from the cross of CIMMYT synthetics and Chinese wheats, is a highly productive wheat cultivar with high resistance to stripe rust. At present, the cultivar was highly resistant to all of popular PST races in China. It is, therefore, important to map the stripe rust resistance gene in Chuanmai 42 with molecular markers.The objectives of this study were to map a stripe rust resistance gene in Chinese wheat cultivar Chuanmai 42 using molecular markers and to investigate its relationship with Yr24 and Yr26. An F2 population with 787 individuals and 186 F3 families derived from the cross of Chuanmai 42 (resistant)/Taichung 29 (susceptiable) were inoculated with Chinese dominating PST isolate CYR32 at seedling stage. The result indicated that stripe rust resistance in Chuanmai 42 was conferred by a single dominant gene, designated as YrCH42. In all, 819 pairs of wheat SSR primers were employed to test the two parents, as well as resistant and susceptible bulks. Subsequently, nine polymorphic markers were used to test the F2 and F3 mapping populations. Results showed that YrCH42 is linked to the nine SSR loci with genetic distances ranging from 1.6 cM to 14.8 cM, and LOD scores ranging from 15.7 to 35.7. Among them, Xgwm498 and Xbarc187 were two SSR markers linked to YrCH42 most closely, with genetic distances of 1.6 cM and 2.3 cM, respectively. YrCH42 was close to the centromere of chromosome 1B. Use of these markers may greatly facilitate resistance gene pyramiding, and improve breeding efforts in achieving durable stripe rust resistance.A total of 197 F2 plants from the cross Chuanmai 42×Yr24/3*Avocet S and 726 F2 plants from Chuanmai 42×Yr26/3*Avocet S showed high resistance to CYR32 without segregations. Seedling testes with 26 PST isolates showed an identical reaction patterns for Chuanmai 42 (YrCH42), Yr24/3*Avocet S (Yr24) and Yr26/3*Avocet S (Yr26). In considering the allelic test of two F2 populations and seedling responses to 26 PST isolates as well as chromosome locations, YrCH42, Yr24 and Yr26 are likely to be the same gene.