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Genetic dissection of partial resistance to race 6 of Venturia inaequalis in apple

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Abstract:

Scab, caused by the fungus Venturia inaequalis, is one of the most important diseases of apple (Malus × domestica). The major resistance gene, Vf, has been widely used in apple breeding programs, but two new races of the fungus (races 6 and 7) are able to overcome this gene. A mapped F1 progeny derived from a cross between the cultivars Prima and Fiesta has been inoculated with two monoconidial strains of race 6. These strains originated from sporulating leaves of 'Prima' and a descendant of 'Prima' that were grown in an orchard in northern Germany. 'Prima' carries the Vf resistance gene, whereas 'Fiesta' lacks Vf. A large variation in resistance and (or) susceptibility was observed among the individuals of the progeny. Several quantitative trait loci (QTLs) for resistance were identified that mapped on four genomic regions. One of them was located in the very close vicinity of the Vf resistance gene on linkage group LG-1 of the 'Prima' genetic map. This QTL is isolate specific because it was only detected with one of the two isolates. Two out of the three other genomic regions were identified with both isolates (LG-11 and LG-17). On LG-11, a QTL effect was detected in both parents. The genetic dissection of this QTL indicated a favourable intra-locus interaction between some parental alleles.Key words: Malus × domestica, partial resistance, Venturia inaequalis, resistance breakdown, quantitative trait locus.

La tavelure, causée par le champignon Venturia inaequalis, est une des plus importantes maladies du pommier (Malus × domestica). Le gène de résistance majeur Vf a été largement utilisé dans les programmes d'amélioration du pommier, mais deux nouvelles races du champignon (races 6 et 7) sont capables de le contourner. Une descendance F1 cartographiée issue du croisement entre les cultivars Prima et Fiesta a été inoculée avec deux souches monospore de race 6. Ces souches avaient été isolées à partir de feuilles sporulantes de 'Prima' ou d'un de ses descendants, dans un verger du nord de l'Allemagne. 'Prima' porte le gène Vf, mais pas 'Fiesta'. Ce dernier est considéré comme modérément sensible en verger. Une grande variation de résistance/sensibilité a été observée dans la descendance. Plusieurs QTLs (« quantitative trait loci ») de résistance ont été identifiés et sont localisés dans quatre régions génomiques. L'un d'eux est situé très proche du gène Vf sur le groupe de liaison LG-1 et est souche spécifique. Deux autres régions génomiques ont été identifiées avec les deux souches (LG-11 et LG-17). Pour le groupe de liaison LG-11, un effet QTL a été détecté chez chaque parent. L'analyse de ce QTL indique une interaction intra-locus favorable entre certains des allèles parentaux.Mots clés : Malus × domestica, résistance partielle, Venturia inaequalis, contournement de résistance, locus de caractère quantitatif.

Document Type: Research Article

Publication date: April 1, 2003

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  • From its inception in 1957, this international cytogenetics journal has catered to the research areas of the members of the Genetics Society of Canada; traditionally, these have included agriculture, entomology, genetics/cytogenetics, and evolutionary mechanisms. The contents of the journal have evolved as contributors developed new technologies and interests. A 20-member Editorial Board is composed of scientists from around the world. Reviews and commentary from respected experts are often featured.
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