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International audience; The production of botrytised wines involves grapes with high sugar concentration and complex aromas caused by the presence of noble rot. The aim of this paper was to characterise botrytised grapes on a physico-chemical basis and therefore identify markers of its evolution. Colour analysis, compression and puncture tests and phenolic profiles were performed in order to identify the potential markers and discriminating tools for the presence of the fungus. Chenin blanc grapes from two parcels in Loire Valley (France) were sampled during a 4-week period. Significant changes of phenolic composition like the total polyphenol which decreases up to 40 % were observed as B. cinerea was more advanced on the berries. Myricetin a compound that has not been reported before in white grapes was found only in highly affected berries. At the same time as the level of infection increases, the presence of the fungus seems to induce, from one side, an increase of catechin, epicatechin and epicatechin gallate, and from the other side, the decrease in caftaric acid, coutaric acid, quercetin-3 glucoside and kaempferol-3 glucoside. Puncture tests appeared to be the more reliable mechanical tool to differentiate between infection levels by itself; however, the combination of puncture and compression tests with colour showed a more significant and clear differentiation. This combination appeared to be the most adequate for stablish markers of noble rot evolution in the conditions studied. A decrease in mechanical resistance of berries' skin (measured by the maximum puncture force required for skin rupture) was observed during infection. These results on botrytised Chenin grapes are new and provide a novel approach for an objective measurement of noble rot in Chenin grapes.

International audience

With the objective to identify previously unknown parental relationships among grapevine cultivars, 352 cultivars of Vitis vinifera L. were analyzed at 17 microsatellite loci. 29 were found to be duplicate genotypes of other cultivars. From the 323 unique genotypes, 89 possible pairs of parents were identified for 52 cultivars (i.e., each putative progeny cultivar shared at least one allele with each putative parent at each of the loci anlayzed). Sixty cultivars were then analyzed with an additional 15 microsatellit e markers and from among these 24 possible pairs of parents were identified for 24 cultivars. Fourteen of the 24 (including Chardonnay, Gamay noir, Aligote, and Melon) are possible progeny of Pinot and Gouais blanc. Two cultivars (Aubin and Petit Meslier) are possible progeny of Gouais blanc and Savagnin (syn. Traminer) and three cultivars (Colombard, Meslier St-Francois and Balzac blanc) are possible progeny of Gouais blanc and Chenin. The possible parents of Syrah were also identified as Dureza and Mondeuse blanche.

In an attempt to develop a technique for the identification of grape cultivars in commercial wines, a method for the extraction of DNA from must and experimental wines was adapted and optimal PCR conditions for the amplification of this DNA were established. DNA was analyzed during the fermentation process for six cultivars (Chardonnay, Clairette blanche, Grenache noir, Merlot, Muscat blanc à petits grains, and Syrah). The extractions were performed on solid parts in suspension as well as on the aqueous fraction. Expected profiles for these cultivars were obtained with DNA extracted from the solid parts during all of the fermentation process and for the wine. The analysis of DNA extracted from aqueous fractions was less reproducible, and microsatellite amplifications were obtained only in the case of Clairette blanche, Merlot, and Syrah wines. Results demonstrate that the purification process is adequate for the analysis but that the DNA concentration represents the main limiting factor. Technical improvements of the method are discussed.