Genetic mapping of the wheat leaf rust resistance gene Lr60 (LrW2)

Leaf rust (caused by Puccinia triticina Eriks.) is an important disease of wheat (Triticum aestivum L.) in North America. This study was conducted to assess the utility of the uncharacterized resistance gene Lr60 (formerly LrW2) for the development of resistant cultivars by demonstrating its novelty, genetic location, and the breadth of resistance that it confers. Haploids of a single gene line carrying Lr60 (RL6172) were pollinated with a susceptible cultivar to generate hybrids with random chromosome deficiencies arising from irregular meiosis of the haploid. Out of 488 hybrids, four were susceptible to leaf rust. All susceptible hybrids lacked several polymorphic microsatellite alleles from RL6172 that are specific to chromosome 1D. Analysis of an F-2 population confirmed that Lr60 was located on the short arm of 1D, 8.4 cM distal to the microsatellite BARC149. Since Lr21 is also located on 1DS a cross was made between single gene lines of Lr21 and Lr60; five susceptible plants recovered in F-2 out of 1141 individuals tested were confirmed with progeny tests. This ratio (5:1136) gives an estimated recombination frequency of 13% between Lr21 and Lr60. RL6172 was tested with 37 isolates of P. triticina, encompassing a diversity of virulence found in North America; one isolate was virulent. Lr60 is a novel resistance gene and represents a useful diversification of the genetic resources available in wheat for development of leaf rust resistant cultivars.