Acceso usuarios
Annik Schnitzler, Claire Arnold, Frédéric Guibal, Jean Michel Walter
The Eurasian wild grapevine Vitis vinifera ssp.
sylvestris ([Gmelin] Hegi) is currently distributed in a few alluvial and colluvial forests around the Mediterranean basin between the 30th and 49th northern parallels, from sea level up to an altitude of 2000m. These areas are refugia where grapevine pest (phylloxera) and fungi diseases (oïdium; mildew) have a restricted spread. These pest and diseases were imported with the American Vitis species at the end of the 19th century. Phylloxera entered floodplains massively thanks to large-scale hydraulic works, which have deprived alluvial zones of regular flooding.
Today, another threat should be taken into account: taxonomic pollution. Gene flows between wild grapevines and the Vitis taxa that escape from vineyards are now occurring.
The taxa may be either European cultivars (Vitis vinifera ssp. vinifera), interspecific cultivars or artificial polyhybrids of American Vitis species used as rootstocks.
In the south of France, a few wild grapevines have been reported along hedges close to the lower Rhône valley. Two other small populations of Vitis sp. were found in two private lands, the Meyranes and the mas Saint-Georges woodlands, in the Camargue delta. In Meyranes, true wild grape vines are very rare, and much less abundant than in the mas Saint-Georges.
The mas Saint-Georges population is particularly rich in Vitis individuals (an estimation of 52 individuals).
Old maps indicate that the mas Saint-Georges woodland was an ancient wetland, dried up after the Rhône embankment at the beginning of the 20th century. The forest stand is thus ca. 100 years old. Wild grapevines have found refugia in this young woodland.
The study aimed to provide insight into this Vitis population through field, ecological and genetic analyses.
The genetic composition and diversity were analyzed on 37 samples. Thirty-one (31) individuals collected were true wild grapevines.
Their genetic diversity was found to be similar to that of other European populations. Four were hybrids/introgressed between rootstocks and wild grapevines, and two were hybrids/introgressed wild grapevines and cultivars We found three haplotypes (H1, H3, H4) in the true wild grapevines: 14 individuals had H1 haplotype, which is common to wild populations of western Europe and largely dominant among true wild grapevines. Four individuals had H3 haplotype, which is common in wild grapevine populations from Central Europe, but also present in some cultivars. Thirteen individual had H4 haplotype, which is common to western grapevines and a few cultivars.
The three haplotypes H1, H3 and H4 found in this population suggest that the Camargue is situated in a convergence zone between populations from west, center and south of the Mediterranean basin.
For hybrids between wild grapevines and rootstocks, we showed that hybridization can occur in both directions.
We measured morphological features. The mean diameter of the population is 4.9cm ± 1.9cm.
The biggest lianas reach 7cm diameter and live in the canopy. Dendrochrological data indicate that these big lianas are 38-50 years old.
True wild grapevines live within the forest and along a few edges, climbing on white poplars, elms and ashes. Hybrids are located only along forest edges. This means that the woodland is closed enough to avoid pollen exchange with exotic Vitis.
Architectural features of the woodland were evaluated with the help of hemispherical photographies. Gap fraction (TG: mean 0.24;
amplitude 0.11-0.30) and canopy openess (CO:
0.20; 0.10-0.26) as well as light extinction coefficient (Kb), Fraction Cover (FC) and Fraction Soil (FS) from nadir view all indicate a relatively high porosity of the canopy to direct light. With regard to this rather high light microclimate in the understories, the native liana can establish sustainably.
However seedlings were not found in this woodland, suggesting that sexual reproduction no longer occurs. The present environment in the delta is thus not suitable for wild grapevine maintenance on the long term. This result fits with conclusions of other studies of wild grapevines in Europe.
In contrast, seedlings from American rootstocks are numerous in the adjacent Meyranes woodland, and globally in the delta. Expansion of these hybrids is helped by abundant fructifications, transported by birds.
Conservation of these last individuals of wild grapevines should be set up with the land owners consent. More ambitious schemes, i.e.
increase in forest cover and return of flooding, would however be necessary for a long term conservation of the species.
La vigne sauvage (Vitis vinifera ssp. sylvestris) est en déclin marqué depuis la fin du xixe siècle.
Depuis 2000, l’espèce est considérée en danger critique d’extinction. Des prospections dans la vallée du Rhône ont montré qu’il existait quelques micropopulations jusque dans le delta.
Une population de 52 pieds de grandes dimensions et présentant un phénotype sauvage a récemment été découverte en rive gauche du Grand Rhône, dans le boisement privé du mas Saint-Georges.
Une recherche pluridisciplinaire a été entreprise sur cette population de vignes afin de reconstituer leur histoire ; les outils utilisés ont été la génétique (effectuée sur 37 individus), l’écologie (dimensions des pieds, identification des porteurs), et la dendrochronologie effectuée sur 5 pieds. L’habitat forestier a également été analysé du point de vue architectural et dynamique de la lumière.
Trente et un (31) individus ont été déterminés comme étant de véritables vignes sauvages, dont la diversité est légèrement inférieure à celle des autres populations européennes. Quatre sont des individus hybrides ou introgressés : deux entre vignes sauvages et vignes américaines, et deux entre vignes sauvages et vignes cultivées.
Trois haplotypes typiques des vignes sauvages ont été déterminés, indiquant que ce site est à un point de convergence entre populations méditerranéennes du sud, de l’ouest et du centre de la Méditerranée.
Le boisement a été suffisamment fermé pour éviter les échanges de pollen avec les vignes américaines échappées.
À partir de ces données et de l’analyse des cartes anciennes, il a pu être déduit que ce boisement s’était développé au début du xxe siècle à partir d’un marais asséché par les aménagements hydrauliques. L’âge des vignes, estimé par la dendrochronologie à une fourchette de 38 à 50 ans, pourrait cependant être de l’âge de la forêt. Les vignes se seraient installées lors de la succession forestière. Les caractéristiques architecturales du boisement (à la fois dense et lumineux) ont permis à la vigne de s’y établir sur une longue durée.
Actuellement, cette population ne se reproduit plus. Les conditions actuelles ne sont donc plus favorables à l’espèce, à l’inverse des populations échappées de porte-greffes, très abondantes en Camargue. Une protection forte de ces derniers pieds de vigne forestière devrait être mise en place avec l’accord des propriétaires.
