Berry fresh weight and composition are under the control of complex interactions among genotype, environmental factors, and viticulture practice, which all affect not only the mean value but also the ranges of variation in berry traits. Both mean values and variation range in berry composition play a role in berry quality and, subsequently, wine typicity. This review examines recent ecophysiological, genetic, and molecular knowledge to provide better understanding of the mechanisms that influence variability in berry weight and composition. We specifically reviewed the variation range in berry weight and composition (including sugars, organic acids, and anthocyanins) among Vitis genotypes, the environmental and viticulture practices that cause variability for a given cultivar, the genetic clues underlying the genotypic variation, and the putative genes controlling berry weight and composition. Despite numerous studies comparing differences in the mean value of a berry trait among different environment conditions and viticulture practices, very few studies have explored the level of variation in response to those factors. Present genetic and molecular studies are mainly focused on identifying genes involved in the control of berry weight and composition, with few considerations of environmental factors that affect their expression. In the future, more effort should be directed toward integration of genetic and molecular work with ecophysiological approaches in an effort to gain novel insights into the cause of variability in grape fresh weight and composition.

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The aim of the present study was t o investigate the effects of an enhanced CO, concentration alone or in combination with drought stress on antioxidative systems of a deciduous (oak; Quercus robur) and an evergreen (pine; Pinos pinaster) tree species. The seedlings were grown for one season in a greenhouse in tunnels supplied with 350 or 700 p L L-' CO,. The experiment was repeated i n a second year. Antioxidants, protective enzymes, soluble protein, and pigments showed considerable fluctuations in different years. Elevated CO, caused significant reductions in the activities of superoxide dismutases i n both oak and pine. The activities of ascorbate peroxidase and catalase were also reduced in most cases. The activities of dehydroascorbate reductase, monodehydroascorbate radical reductase, glutathione reductase, and guaiacol peroxidase were affected little or not at all by elevated CO,. When the trees were subjected to drought stress by withholding water, the activities of antioxidative enzymes decreased in leaves of pine and oak grown at ambient CO, and increased in plants grown at elevated CO, concentrations. The present results suggest that growth i n elevated CO, might reduce oxidative stress to which leaf tissues are normally exposed and enhance metabolic flexibility t o encounter increased stress by increases in antioxidative capacity.Most predictions suggest that the current mean ambient CO, concentration of 355 pL L-' will approximately double by the end of the next century (Roeckner, 1992). Increasing concentrations of CO, and of other greenhouse gases will result in an increase in mean temperature and cause changes in precipitation patterns (Roeckner, 1992). Climate models predict large-scale drought periods during summer for northern mid-latitudes (Roeckner, 1992). The availability of water is one of the most important factors determining vegetation diversity and plant productivity (Rochefort and Woodward, 1992). The effects of water deficits on plant performance and growth are mediated through decreases in stomatal conductance and photosynthesis and depend on the severity and duration of the drought period, the '

Background and Aims:  Grafting is used in viticulture worldwide. Rootstocks are known to alter scion development or ‘confer vigour’ to varying degrees. This work examines scion/rootstock interactions in young grafted grapevines. Its aim was to determine the effects of scion and rootstock genotypes on biomass allocation within the plant. Methods and Results:  Five months after grafting, biomass allocation between the root and the shoot was measured for all the scion/rootstock combinations made between three Vitis genotypes. The scion genotype explained the highest percentage of the non‐random variance for biomass allocation within the plant, including biomass allocation to the roots, i.e. it conferred differences in root vigour. In addition, we developed a double‐grafted system, in which a single scion was grafted onto two rootstocks, to analyse further scion (or carbon source) effects on root development. Conclusions:  This work provides evidence of conferred root vigour by the scion which does not appear to be related to carbon supply from the shoot. The genotypes studied display varying levels of plasticity in their response to different grafting partners. Significance of the Study:  This work presents detailed analysis of biomass allocation within young grafted vines. In young grafted grapevines, the scion genotype has a major effect on most parameters of development, especially in the root. This aspect of rootstock/scion interactions should be taken into account when selecting rootstocks. A double‐grafting system was developed for future research on signalling pathways and exchange mechanisms between scion and rootstock in grafted grapevine.

Background and Aims: Both rootstocks and mineral nutrition, particularly nitrogen (N), are known to affect many aspects of plant development including the control of scion vigour. In this study, we investigated the role of the rootstock genotype in grafted grapevine responses to N supply in terms of the root and leaf ionomes, scion vigour and whole plant biomass. Methods and Results: Vitis vinifera cv. Cabernet Sauvignon was grafted on two rootstock genotypes known to confer high and low vigour. Plants were grown for 60 days under three levels of nitrate supply. Stem, leaf, trunk and root biomass, and the concentration of 13 macroelements and microelements in roots and leaves were measured. High scion vigour was associated with a high concentration of elements in the leaves. The concentration of some elements in the leaves, such as phosphorus, was affected by the N supply differently in the two scion/rootstock combinations. Conclusion: Differences in rootstock conferred vigour were associated with particular shoot and root ionome profiles, and these responses were dependent on N supply. Significance of the Study: These results demonstrate that rootstocks alter scion growth and the leaf ionome in response to N supply.

The dynamics of sugar (hexose) concentration in ripening grape berries (Vitis vinifera L.) were simulated with a refined mechanistic model. Changes in sugar concentration were reproduced by the sum of sugar import (S), sugar metabolism (M) and water budget (W). S and W were derived from model inputs of fresh and dry mass, and M was simulated with a relative metabolism rate describing the depletion of hexose. The relative metabolism rate was associated with the relative growth rate of dry mass with a coefficient (k) that was constant for a given cultivar under various growth conditions (temperature, water supply, and source-sink ratio) but varied with genotype. The k value was~20% higher for cv. Merlot than for cv. Cabernet Sauvignon, indicating more imported sugars would be depleted by Merlot than Cabernet Sauvignon. The model correctly simulated the negative effect of lowered leaf-to-fruit ratio and the positive effect of water shortage on sugar concentration. Sensitivity analysis revealed that the present model was weakly sensitive to k because of sugar accumulation being predominantly controlled by S, with M relatively small (~20%) with respect to the increment of sugar concentration. Model simulation indicated that the decreasing leaf-to-fruit ratio reduced S more than M and W, causing a net decrease in sugar concentration. In contrast, the water shortage decreased S less than M and W, resulting in a net increase in sugar concentration.

Summary — The purpose of this study was to explain large differences in growth and decline of the pedunculate oak (Ouercus robur L) and the sessile oak (Q petraea Liebl) observed in the forest as a result of drought. In addition, northern red oak (Q rubra L) was compared with the 2 indigenous oaks. The effects of controlled soil water deficits on growth and water relations of young plants of these 3 species grown in large boxes have been studied. The plants were old enough to have developed normal root systems. Two species were planted in each box, and submitted to very similar patterns of water stress. Predawn leaf water potential, stomatal conductance, net assimilation rates, shoot elongation and mortality were monitored. The effect of an overall improvement in mineral nutrition on these parameters was also tested. During water deficit (decrease in predawn leaf water potential), the pattern of decrease of gas exchange was similar for the 3 species. Thus, their ability to limit water deficit by reduction of transpiration was similar. On the other hand, shoot growth of Q rubra was more reduced than that of Q robur for similar predawn leaf water potential; growth of Q petraea was the least sensitive. However, increase of mineral nutrition improved the growth of both Q robur and Q rubra, but not that of Q petraea. For the 3 species, no mortality was noted as long as predawn leaf water potentials remained > -3.6 MPa. Below this limit, the mortality rate was highest in Q robur, Q petraea and lowest in Q rubra. These differences in mortality between species are due to differences in tolerance to water stress, not in avoidance.drought / growth I gas exchange I dieback I fertilization I Quercus Résumé — Différences dans la résistance à la sécheresse de 3 espèces de chêne à feuilles caduques, cultivées en conteneurs.