Molecular and phenotypic characterization of seedling and adult plant leaf rust resistance in a world wheat collection.

Genetic resistance is the most effective approach to managing wheat leaf rust. The aim of this study was to characterize seedling and adult plant leaf rust resistance of a world wheat collection. Using controlled inoculation with ten races of , 14 seedling resistance genes were determined or postulated to be present in the collection. , , and were the most prevalent genes around the world while , , and/or and were rare. To confirm some gene postulations, the collection was screened with gene-specific molecular markers for , , and . Although possessing the and/or gene-specific marker, 51 accessions showed unexpected high infection types to race BBBD. The collection was tested in the field, where rust resistance ranged from nearly immune or highly resistant with severity of 1 % and resistant host response to highly susceptible with severity of 84 % and susceptible host response. The majority of the accessions possessing the adult plant resistance (APR) gene had a maximum rust severity of 0-35 %, similar to or better than accession RL6058, a Thatcher- near-isogenic line. Many accessions displayed an immune response or a high level of resistance under field conditions, likely as a result of synergy between APR genes or between APR and seedling resistance genes. However, accessions with three or more seedling resistance genes had an overall lower field severity than those with two or fewer. Immune or highly resistant accessions are potential sources for improvement of leaf rust resistance. In addition, some lines were postulated to have known but unidentified genes/alleles or novel genes, also constituting potentially important sources of novel resistance.