The wheat cultivars Westphal 12A and BH1146 were characterized in previous studies as having partial resistance to the leaf rust pathogen Puccinia triticina. In the present study, genetic analysis showed that Westphal 12A has three genes that condition resistance in seedling plants, and the gene Lr34, which is optimally expressed in adult plants. The three seedling resistance genes in Westphal 12A may be new leaf-rust resistance genes. BH1146 was shown to have the adult plant resistance genes Lr13 and Lr34. Many wheat cultivars with partial resistance to leaf rust may have Lr13 and/or Lr34, or other previously described Lr genes.

A genetic analysis of the landrace-derived wheat accessions Americano 25e, Americano 26n, and Americano 44d, from Uruguay was conducted to identify the leaf rust resistance genes present in these early wheat cultivars. The three cultivars were crossed with the leaf rust susceptible cultivar ÔThatcherÕ and approximately 80 backcross (BC1) F 2 families were derived for each cross. The BC1F 2 families and selected BC1F 4 lines were tested for seedling and adult plant leaf rust resistance with selected isolates of leaf rust, Puccinia triticina. The segregation and infection type data indicated that Americano 25e had seedling resistance genes Lr3, Lr16, an additional unidentified seedling gene, and one adult plant resistance gene that was neither Lr12 nor Lr13, and did not phenotypically resemble Lr34. Americano 26n was postulated to have genes Lr11, Lr12, Lr13, and Lr14a. Americano 44d appeared to have two possibly unique adult plant leaf rust resistance genes.Key words: Triticum aestivum -Puccinia triticina -wheat leaf rust -adult plant resistance -seedling resistanceThe wheat accessions Americano 25e, Americano 26n, and Americano 44d, were derived from landraces in Uruguay in the early 20th century (Kohli 1986). Americano 26n and Americano 44d were released by ÔA. BoergerÕ as cultivars in 1918. In Uruguay, these accessions were among the parents used for the early cultivars Artigas (Americano 25e/Americano 26n, 1924), Larranaga (Americano 25e/Pelon 33c, 1926), ACD 11 (Americano 44d/Pelon 33c, 1931) and Porvenir (Americano 26n/ Pelon IV, 1935). In Argentina, Americano 26n, also known as Klein Universal I, was used as a parent for Klein Record (1925) and Klein H 51 (1929). Americano 44d, also known as Klein Universal II, was used as a parent for Klein Vencedor (1925), Klein Sin Rival (1925), Klein Ceres (1926) and Klein Titan (1925. Americano 25e was used as a parent for Klein San Martin (1926), Klein Mammuth (1927) and Klein Triunfo (1929. These early Uruguayan and Argentine wheats were subsequently used as parents for later cultivars in both countries and also in Brazil (Kohli 1986).Wheat leaf rust, caused by Puccinia triticina Eriks., is an important disease of wheat in South America and worldwide. In recent years, increased susceptibility to leaf rust has been a major cause of cultivar replacement in Uruguay, as the leaf rust pathogen is genetically diverse and virulent races can rapidly increase (German 1996). Wheat cultivars from South America have been a rich source of important leaf rust resistance genes (Dyck et al. 1966, Dyck and Kerber 1977, 1981. Over 50 leaf rust resistance genes have been mapped and given gene designations (McIntosh et al. 2005), however relatively few genes still condition effective resistance to the leaf rust pathogen. This study was undertaken to identify the leaf rust resistance genes present in accessions of Americano 25e, Americano 26n and Americano 44d, in order to determine if new uncharacterized leaf rust resistance genes are possibly present in these three landra...