Mapping Yr28 and other genes for resistance to stripe rust in wheat

Stripe (yellow) rust, caused by Puccinia striiformis West., is an important constraint to wheat production in cool environments. With the purpose of i dentifying genes for resistance to the disease, a RFLP mapping population o f recombinant inbred lines developed from a synthetic [Triticum turgidum L. x Aegilops tauschii (Coss.) Schmal.] x T. aestivum L. cv. 'Opata 85' cross was visually evaluated for seedling infection type in three greenhouse ino culation tests and for adult-plant disease severity in Pour field tests at Celaya and Toluca, Mexico. A previously unidentified gene from Ae. tauschii , designated as Yr28, was located on chromosome arm 4DS. Although Yr28 stro ngly influenced seedling resistance, it showed a strong effect in adult pla nts at only the warmer of the two field sites. A second gene showed high en vironmental sensitivity in seedling tests, with resistance associated with Opata marker alleles near the adult-plant resistance (APR) gene Yr18 on chr omosome arm 7DS. Gene Yr18, known to be present in Opata, strongly reduced disease response in field trials and was tightly linked with leaf-rust resi stance gene Lr34. Three other regions from Opata on chromosome arms 3BS, 3D S, and 5DS were also associated with APR.