YrF: a Race-Specific Resistance Gene to Stripe Rust in Francolin#1

Francolin#1, a high yielding spring wheat line developed by the International Maize and Wheat Improvement Center (CIMMYT), displays good agronomic characters and stable resistance to current populations of the three rusts. The genetic basis of resistance to stripe rust in Francolin#1 was investigated using a population of 141 F₅ recombinant inbred lines (RILs) derived from a cross with the susceptible line Avocet-YrA. The parents and RILs were phenotyped thrice as seedlings in the greenhouse with races of Puccinia striiformis f. sp. tritici prevalent in Mexico. Parents and RILs were also phenotyped for stripe rust resistance in field trials for two years at Toluca (Mexico) and one year at Sichuan (China) and Greytown (South Africa) under high disease pressure. Segregation results in seedlings and molecular marker analyses indicated the presence of a temporarily designated gene YrF in Francolin#1 for resistance to stripe rust. YrF conferred intermediate seedling reactions and moderate resistance at adult plants in Mexican, Chinese and South African environments. It was located on chromosome 2BS and explained 10.4-27.9% of stripe rust severity variance in the adult plant across three inter-continental environments. The flanking markers for YrF were Xgwm374 and Xwmc474 within 2.0 cM and 1.8 cM, respectively, which can be useful for marker assisted selection in wheat rust breeding based on the testing of 350 advanced wheat lines. YrF, in combination with adult plant resistance genes Yr29 and Yr30, also mapped in the population, conferred a high level of resistance to stripe rust at the three locations.