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QTL ANALYSIS OF PATHOGEN RESISTANCE FACTORS AND RIPENING TIME TRAITS IN A GENETIC MAP FROM GRAPEVINE BREEDING LINE GF.GA-47-42 CROSSED TO 'VILLARD BLANC'

Marker-assisted selection is an important tool of current grapevine breeding which aims to improve cultivars for more sustainable viticulture. Markers genetically linked to traits of interest are hence required. These can be identified by QTL (quantitative trait loci) analysis scanning genetic maps elaborated from controlled crosses for marker genotypes correlating with segregating phenotypes. Major traits of interest are resistances to pathogens like powdery and downy mildew (Erysiphe necator resp. Plasmopara viticola) of leaves and fruits. In addition, phenological traits have recently acquired special attention. Breeders wish to select grapes with a better defined “window” of ripening time as ripening behavior affects both pathogen susceptibility and fruit quality. Ripening time needs to be considered within the context of the climate change debate. To identify genomic regions carrying loci affecting resistance traits and ripening time we constructed a genetic map using 151 individuals from the cross of grapevine breeding line Gf.GA- 47-42 (‘Bacchus’ × ‘Seyval’) with ‘Villard blanc’ (‘Seibel 6468’ × ‘Subereux’). Both parental lines are resistant to powdery and downy mildew and vary considerably in “véraison” time as an indicator of ripening. While Gf.GA-47-42 is rather early, ‘Villard blanc’ exhibits middle to late “véraison” and this trait segregates clearly in the cross. Linkage/recombination analysis for map construction was based on more than 350 simple sequence repeat (SSR)-derived markers. Many of these loci were newly extracted from the Vitis reference genome sequence of PN40024 (http://www.genoscope.cns.fr/externe/GenomeBrowse r/Vitis/). In addition, the mapping included 210 newly developed SNP (single nucleotide polymorphisms) markers. A subset of these was analyzed with two different techniques permitting to assess the reliability of SNP genotyping with both methods. The resulting map was scanned for QTL influencing powdery and downy mildew disease resistance and the time of “véraison”. Several major QTL were identified.

grapevine; Erisyphe necator; Plasmopara viticola; resistance loci; veraison; Vitis sp.

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