Water deficit responses for tolerant varieties to downy and powdery mildew

Abstract

Fungus disease-tolerant grape varieties appear to be a solution to cope with reduction of phytosanitary spraying in the vineyard as well as increasing disease pressure. In early 2000, INRAE launched a new breeding programme named Resdur that aimed at creating new grapevine varieties with sustainable resistance to downy and powdery mildew and suitable traits for high quality wines production. However, the performances of these varieties in response to water shortage is not yet well characterized. This study aims at characterizing the responses to water deficit of ten fungus disease-tolerant varieties in comparison to four Vitis vinifera cultivars (Cabernet-Sauvignon, Grenache, Syrah, and Pinot noir). To assess these responses under controlled water deficit conditions, plants were grafted onto two rootstocks (SO4 and 110R), grown in pots in natural loamy clayey soil under greenhouse conditions. Two watering regimes were applied, well-watered set at 85% of soil water content, and a mild water deficit set at 40% of soil water content. Several physiological traits were monitored during the experiment: defoliation levels, leaf area, shoot and root biomass, shoot length, transpiration, and δ13C measured on leaves grown in each condition. Defoliation levels responded significantly to a variety effect with 45% of the variance explained. Genotype effect was also reported on shoot and root biomass with 28% and 29% of explained variance, respectively. Similarly, genotypes affected 23% of transpiration under both watering conditions. Rootstock effect is more limited with 19% of explained variance only for the shoot biomass. Moreover, significant rootstock effect was limited to shoot biomass under water deficit conditions. No significant differences between fungus disease-tolerant varieties and Vitis vinifera cultivars was reported for the following traits: shoot and root biomass, transpiration for both conditions and defoliation levels. Genotype ranking was not consistent across studied traits indicating that varieties responded to drought in a complex way. One major conclusion of our study is that the genotype effect is significant for most studied traits. The consequences of such genotype effects on drought tolerance should now be studied under field conditions on fruit bearing vines.