ABSTRACT
Leaf rust is one of the most destructive diseases affecting wheat worldwide. The most effective way to control it is to use resistant cultivars. Resistance based on slow-rusting adult plant resistance (APR) genes has proven to be the best method for developing cultivars with durable resistance. A source of slow-rusting APR for leaf rust is the Brazilian wheat cultivar Toropi. The Toropi/IAC 13 F2 and F7 recombinant inbred lines (RILs) were developed in previous studies. Phenotypic analysis of the F2 and F7 RILs showed that 2 recessive genes that were temporarily named trp-1 and trp-2 conferred APR in Toropi. In the present study, we used monosomic families and amplified fragment length polymorphism (AFLP), sequence-tagged site, and simple sequence repeat (SSR) markers to map trp-1 and trp-2 on wheat chromosomes. Analysis of the F2 monosomic RIL showed that trp- 1 and trp-2 were located on chromosomes 1A and 4D, respectively. AFLP analysis of the F7 RIL identified 2 independent AFLP markers, XPacgMcac3 and XPacgMcac6, which were associated with Toropi APR. These markers explained 71.5% of the variation in the phenotypic data in a multiple linear regression model. The AFLP markers XPacg/ Mcac3 and XPacg/Mcac6 were anchored by SSR markers previously mapped on the short arms of chromosomes 1A (1AS) and 4D (4DS), respectively. The trp-2 gene is the first leaf rust resistance gene mapped on wheat chromosome 4DS. The mapping of trp-1 and trp-2 provides novel and valuable information that could be used in future studies involving the fine mapping of these genes, as well as in the identification of molecular markers that are closely related to these genes for marker-assisted selection of this important trait in wheat.
Subject(s)
Chromosome Mapping/methods , Disease Resistance/genetics , Genes, Plant/genetics , Monosomy/genetics , Plant Diseases/genetics , Plant Leaves/microbiology , Triticum/genetics , Amplified Fragment Length Polymorphism Analysis , Analysis of Variance , Basidiomycota/physiology , Brazil , Chromosome Segregation/genetics , Chromosomes, Plant/genetics , Crosses, Genetic , Disease Resistance/immunology , Genetic Markers , Microsatellite Repeats/genetics , Plant Diseases/immunology , Plant Diseases/microbiology , Plant Leaves/genetics , Polymorphism, Genetic , Triticum/immunology , Triticum/microbiologyABSTRACT
Adult plant resistance to leaf rust in the Brazilian wheat cultivar Toropi (Triticum aestivum) was studied in crosses with the susceptible cultivar IAC 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 to 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 in the greenhouse environment. Necrosis was expressed when the two homozygous recessive genes occurred together in the F2, independently of the response to leaf rust. The resistance and leaf-necrosis genes differ from those previously reported in wheat. Segregation for leaf-rust resistance in the field at Passo Fundo, Brazil, fit a 1:3 ratio for a single recessive gene. With a different pathogen race, and in crosses of cvs. Toropi and ThatcherLr34, two recessive genes and a dominant gene for resistance were detected in the field in Mexico. The dominant gene was likely Lr34 from cv. ThatcherLr34 and the two recessive genes were likely those detected in the greenhouse adult plants tests at Passo Fundo.
