Inheritance of adult plant leaf rust resistance in the Brazilian wheat cultivar Toropi

Adult plant resistance to leaf rust in the Brazilian wheat cultivar Toropi (Triticum aestivum) was studied in crosses with the susceptible cultivar IA C 13. Cvs. Toropi and IAC 13 are susceptible at the seedling stage to race LCG-RS of Puccinia triticina Erikss., and to all other known Brazilian leaf -rust races. Thus, the resistance observed in Toropi in the field was due t o adult plant-resistance genes. In the greenhouse at the adult plant stage, resistance segregated in a 7:9 ratio for two complementary recessive genes . Additionally, two recessive genes for leaf-tip necrosis were identified i n the greenhouse environment. Necrosis was expressed when the two homozygou s recessive genes occurred together in the Fz, independently of the respons e to leaf rust. The resistance and leaf-necrosis genes differ from those pr eviously reported in wheat. Segregation for leaf-rust resistance in the fie ld at Passe Fundo, Brazil, fit a 1:3 ratio for a single recessive gene. Wit h a different pathogen race, and in crosses of cvs. Toropi and ThatcherLr34 , two recessive genes and a dominant gene for resistance were detected in t he field in Mexico. The dominant gene was likely Lr34 from cv. ThatcherLr34 and the two recessive genes were likely those detected in the greenhouse a dult plants tests at Passe Fundo.