Dosage Effect of Lr3 Gene in the Triticum aestivum–Puccinia recondita Specific Interaction

Gene dosage e€ects of Lr3 gene were studied in the Triticum aestivum±Puccinia recondita tritici speci®c interaction. Deletion-duplication lines carrying di€erent doses of Lr3 gene in chromosome 6B were obtained from a cross between standard Sinvalocho MA wheat and an isogenic translocated Sinvalocho MA 1BS/6BS- 1BL/6BL line. Cytogenetic analysis and assessment of pathogen development revealed evidence for Lr3 gene dosage dependence in the expression of both resistance and avirulence. Increasing doses of chromosome 6B, from nullisomic to tetrasomic condition, increased the resistance, reaching the maximum at the tetrasomic level. The role of reciprocal translocations in the evolution of disease resistance genes in hexaploid wheat, the duplication of genes for resistance as a strategy to be used in plant breeding and the implications of gene- dosage dependence in host±parasite associations are discussed.