The Role of Lr1O, Lrl3, and Lr34 in the Expression of Adult-Plant Resistance to Leaf Rust in the Wheat Cultivar Era. Z. A. Pretorius, Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa. A. P. Roelfs, Cereal Rust Laboratory, University of Minnesota, St. Paul 55108. Plant Dis. 80:199-202. Accepted for publication 16 October 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0199.

Elucidation of the genetic basis of the highly effective resistance in Era wheat to Puccinia re-condita f. sp. tritici could assist breeders in reconstructing similar Lr gene combinations in other cultivars. Attempts to relate the presence of Lr10, Lrl3, and Lr34 with the expression of adult-plant resistance showed that a combination of these genes did not necessarily confer high levels of resistance to pathotype UVPrt8 of P. r. f. sp. tritici. The most resistant adult F2 plant derived from a cross between Era and line RL6058 was homozygous for Lr10, Lrl3, and Lr34, but other F2 plants exhibiting intermediate levels of adult-plant resistance also appeared homo-zygous for all three genes. In the leaf rust-susceptible background of Line E, no clear relationship between Lr13 and expression of adult-plant resistance derived from Era was observed. Limited evidence was obtained that Lr10 in association with an unknown gene or Lrl3 interacted with Lr34 to confer an improved level of resistance to leaf rust in certain plants. Mostly results indicated a lack of interaction among Lr10, Lrl3, and Lr34. It seems unlikely that wheat breeders will be able to reconstruct a similar Era-type of leaf rust resistance by combining Lr10, Lr13, and Lr34