Wilhelm De Almeida Luciana

Abstract :

The increase in water demand caused by climate change in certain regions affects all crops, potentially altering yield and fruit composition. Perennial fruit crops face both short-term fluctuations and long-term cumulative effects of water deficit (HD). Understanding the seasonal and multi-annual effects of HD on fruit production and composition is challenging, but essential. Because of the need to reduce the pesticide footprint in viticulture, many breeding programmes are proposing new interspecific Vitis hybrids that, unlike V. vinifera L., are tolerant to a range of fungal diseases. However, in most breeding programmes, the DH response of grapevine genotypes is not taken into account. In this context, the aim of this work was to characterise the behaviour of a new panel of fungal disease-tolerant genotypes under DH conditions. The behaviour of 6 genotypes from the INRAE breeding programme, compared with that of V. vinifera Syrah as a control, was evaluated in two different experimental contexts, under field conditions and on potted plants in a phenotyping platform.

The objectives were to characterise their water use efficiency (WUE), identify the strategies adopted by the genotypes to cope with cumulative DH, understand C allocation trade-offs within berry metabolites, and explore whether the LowSugarBerry (LSB) trait could provide an advantage under DH. The main results of this work show that: All genotypes improve their WUE at leaf and plant level under DH compared to well-irrigated plants, with genotypes G14 and 3176N standing out for higher water use efficiency than Syrah. The genotypes adopt different acclimatisation strategies to cope with DH, but maintain a fairly stable ranking from one year to the next in terms of fruit-leaf balance and soluble sugar (SS) concentrations in the grapes. On this basis, the genotypes can be divided into three groups, taking into account both the levels and stability over time of four major plant balance and production parameters (yield per plant, fruit-leaf ratios, SS concentrations and organic acid/SS ratio in berries). In general, the 3176N, Syrah and G14 genotypes showed higher production and a more balanced leaf-to-fruit ratio than the Floreal and 3159B varieties.

Apart from the variations in SS associated with the LSB trait, this parameter was stable for all the genotypes, whatever the water regime and experimental conditions. DH systematically increased tartaric acid concentration in all genotypes, while malate consumption varied according to genotype (Artaban showing the highest consumption). Accumulation of thiol precursors and anthocyanins also varied between genotypes, with 3176N standing out for its high levels of both parameters. LSB genotypes did not show any particular response strategy to DH compared to genotypes with normal sugar content. However, to fully understand whether a decoupling of water/C demand in the fruit of these genotypes could confer an advantage with respect to DH, it is important to standardise the plants in terms of fresh weight yield and biomass (at equivalent water and C demand, respectively). Finally, after analysing and comparing the variables under two different experimental conditions, we identified a certain group of variables (e.g. gs) that enabled us to categorise the genotypes under conditions of high DH, and the response to DH from the organ level to the plant level.

Key words : resistant varieties, drought, climate change, viticulturevariétés résistantes, sécheresse, changement climatique, viticulture