Interactions of Lr13 or Lr34 with other leaf rust resistance genes, pathogen isolates and the environment

Leaf rust resistance genes Lr13 and Lr34 are associated with durable resistance, thermosensitivity, and reported to be more effective in the adult than at the seedling stage. They also enhance the effectiveness of additional genes. The objectives of the study were: (1) to characterize the expression of resistance on combinations of Thatcher (Tc) isolines TcLr13, TcLr34 or TcLr13,34 , environments, and an array of isolates with which these genes showed different degrees of compatibility; (2) to determine the consistency among different approaches utilized to identify resistance due to Lr13 and/or Lr34; and (3) to identify the effect of environment, isolates, and specific leaf rust resistance gene combinations with other Lr genes, on the expression of resistance of Lr13 and Lr34. Seven resistance parameters, measured from seedlings or adult plants, were evaluated and compared among themselves. Seedlings of lines with single resistance genes and pair-wise combinations with Lr13 or Lr34 were inoculated with different pathogen isolates to study gone interactions. Two temperatures were utilized to allow for the expression of Lr13 and Lr34. Resistance due to Lr34 was reliably detected as seedling infection type at 15°C. This is the most practical option to identify Lr34. The area under the disease progress curve was highly correlated with every other disease assessment parameter and detected more differences among host genotypes. Lr13 was reliably identified as low adult infection types for both 15°C and 25°C. The resistance due to Lr13 and Lr34 was enhanced by their interaction. Enhancement of resistance was also observed in combinations of Lr13 or Lr34 with other Lr genes in specific pathogen : environment : isoline combinations. Genes apparently ineffective when alone appeared to be effective when combined. The recognition of these gene interactions should provide procedures to better identify resistance genes in breeding programs.