RESUMO
Apple scab, caused by the fungal pathogen Venturia inaequalis, is one of the most severe diseases of apple worldwide. It is the most studied plant-pathogen interaction involving a woody species using modern genetic, genomic, proteomic and bioinformatic approaches in both species. Although 'Geneva' apple was recognized long ago as a potential source of resistance to scab, this resistance has not been characterized previously. Differential interactions between various monoconidial isolates of V. inaequalis and six segregating F1 and F2 populations indicate the presence of at least five loci governing the resistance in 'Geneva'. The 17 chromosomes of apple were screened using genotyping-by-sequencing, as well as single marker mapping, to position loci controlling the V. inaequalis resistance on linkage group 4. Next, we fine mapped a 5-cM region containing five loci conferring both dominant and recessive scab resistance to the distal end of the linkage group. This region corresponds to 2.2 Mbp (from 20.3 to 22.5 Mbp) on the physical map of 'Golden Delicious' containing nine candidate nucleotide-binding site leucine-rich repeat (NBS-LRR) resistance genes. This study increases our understanding of the complex genetic basis of apple scab resistance conferred by 'Geneva', as well as the gene-for-gene (GfG) relationships between the effector genes in the pathogen and resistance genes in the host.
Assuntos
Resistência à Doença/genética , Genes de Plantas , Malus/genética , Malus/microbiologia , Família Multigênica , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Segregação de Cromossomos/genética , Cruzamentos Genéticos , Epistasia Genética , Ligação Genética , Loci Gênicos , Genótipo , Interações Hospedeiro-Patógeno , Modelos Genéticos , Fenótipo , Mapeamento Físico do Cromossomo , Polimorfismo de Nucleotídeo Único/genética , Análise de Sequência de DNA , Esporos Fúngicos/fisiologiaRESUMO
The wild apple (Malus sieversii) is a large-fruited species from Central Asia, which is used as a source of scab resistance in cultivar breeding. Phytopathological tests with races of Venturia inaequalis were performed to differentiate scab-resistance genes in Malus as well as an avirulence gene in the pathogen. A novel gene-for-gene interaction between V. inaequalis and Malus was identified. The locus of the scab-resistance gene Vh8 is linked with, or possibly allelic to, that of the Vh2 gene in Malus pumila Russian apple R12740-7A, at the lower end of linkage group 2 of Malus. Race 8 isolate NZ188B.2 is compatible with Vh8, suggesting the loss or modification of the complementary AvrVh8 gene, while isolate 1639 overcomes both Vh2 and Vh8, but is incompatible with at least one other gene not detected by any of the other race isolates tested. Our research is the first to differentiate scab-resistance genes in a putative gene cluster in apple with the aid of races of V. inaequalis.
