Physiological response of new cultivars resistant to fungi confronted to drought in a semi-arid Mediterranean area

Abstract

Context and purpose of the study – Water is one of the most limiting factors for viticulture in Mediterranean regions. Former researches showed that water shortage hampers both vegetative and reproductive developments. INRA is running programs to breed varieties carrying QTL of tolerance to major fungi, i.e. powdery and downy mildews. Some varieties have been already certified or are close to be certified. However, little is known about the response of these varieties to water deficit, which behavior is critical for their development. This study characterized physiological responses of 4 new varieties to water deficit and described relationship between them.
Material and methods – This experiment was carried out in 2018 the south of France at the INRA’s Experimental Unit of Pech Rouge (Gruissan). Five cultivars were studied: INRA 1, 2, 3 and 4 in comparison to Syrah, all genotypes being grafted on 140Ru. Each cultivar was represented by 60 vines, with 30 vines being irrigated (I) and 30 vines without irrigation (NI). Each treatment x genotype was done in triplicated (3 x 10 vines). Irrigation was applied weekly from 3rd July until 11th September. Predawn leaf water potential (ѰPd) was measured weekly from mid-July to mid-September. When ѰPd between I and NI treatments were evidenced, physiological measurements –photosynthesis (A), stomata conductance (gs) and transpiration (E)- were weekly performed and water use efficiency (WUE= A/E) was calculated.
Results – In all varieties, we observed variations of ѰPd between I and NI, with Syrah and INRA 2 showing the maximum and minimum difference respectively. A, gs and E decreased for all genotypes in relation with ѰPd. Syrah showed the lowest ѰPd (-0.66 MPa averagely), A, gs and E. WUE in all of the varieties, exception INRA 3, was increased as water potential decreased, but in INRA 3 WUE slightly decreased in less values of ѰPd. The physiological parameters were classified to three level of predawn water potential: [0.2-0.4] MPa (moderate stress), [0.4-0.6] MPa (strong stress) and [0.6-0.8] MPa (severe stress) respectively. Under moderate stress, INRA 1 showed the higher A with 9.7 µmol m-2 S-1, but gs and E were maximum for INRA 4. Under a severe water deficit, A and WUE of INRA 1 were 6.44 µmol m-2 S-1 and 2.85 respectively, which is higher than other varieties, indicating INRA 1 as the most drought tolerant variety. These first results should not be considered conclusive.