Grafting cv. Grechetto Gentile Vines to New M4 Rootstock Improves Leaf Gas Exchange and Water Status as Compared to Commercial 1103P Rootstock

Abstract

M4 is a relatively new rootstock that was selected for increased resilience of vineyards across hot regions where meteorological drought is often coupled to water scarcity. However, M4 has thus far been tested only against water-stress sensitive rootstocks. Against this backdrop, the aim of the present work is to examine the water status and gas exchange performances of vines grafted to M4 in comparison to those of vines grafted to a commercial stock that is drought-tolerant, 1103 Paulsen (1103P), under a progressive water deficit followed by re-watering. This study was undertaken on Grechetto Gentile, a cultivar that is renowned for its rather conservative water use (near-isohydric behavior). While fifty percent of both grafts were fully irrigated (WW), the remaining underwent progressive water stress by means of suspending irrigation (WS). Soil and leaf water status, as well as leaf gas exchanges, along with chlorophyll fluorescence, were followed daily from 1 day pre-stress (DOY 176) until re-watering (DOY 184). Final leaf area per vine, divided in main and lateral contribution, was also assessed. While 1103P grafted vines manifested higher water use under WW conditions, progressive stress evidenced a faster water depletion by 1103P, which also maintained slightly more negative midday leaf water potential (Ψleaf) as compared to M4 grafted plants. Daily gas exchange readings, as well as diurnal assessment performed at the peak of stress (DOY 183), also showed increased leaf assimilation rates (A) and water use efficiency (WUE) in vines grafted on M4, which were also less susceptible to photosynthetic downregulation. Dynamic of stomatal closure targeted at 90% reduction of leaf stomatal conductance showed a similar behavior among rootstocks since the above threshold was reached by both at Ψleaf of about −1.11 MPa. The same fractional reduction in leaf A was reached by vines grafted on M4 at a Ψleaf of −1.28 MPa vs. −1.10 MPa measured in 1103P, meaning that using M4 as a rootstock will postpone full stomatal closure. While mechanisms involved in improved CO2 uptake in M4-grafted vines under moderate-to-severe stress are still unclear, our data support the hypothesis that M4 might outscore the performance of a commercial drought-tolerant genotype (1103P) and can be profitably used as a tool to improve the resilience of vines to summer drought.

Grapevine Rootstocks Differently Affect Physiological and Molecular Responses of the Scion under Water Deficit Condition

“…This conclusion was further supported by the higher daily water loss measured in Cab/M4 than in the other combinations under WD (Figure S2). Interestingly, Frioni and co-workers obtained similar results in long-time experiments comparing graft combinations in which the cultivar Grechetto gentile was grafted on M4 or 1103 Paulsen rootstocks [41].…”

“…The union of the rootstock with the scion by means of the grafting practice produces a new plant with phenotype having peculiar characteristics, which depend not only on the contribution of the two different genetic backgrounds but also on the reciprocal influences between the two partners [6][7][8]16,17,19,[35][36][37]40,41]. Considering the importance of preserving the typical features of the grape that are mainly linked to the scion genotype, the more promising strategy to improve the tolerance of grapevine to abiotic stresses, such as water deficiency (WD), is to select new tolerant rootstocks [7,36].…”

“…Following exposure to drought, g s rapidly dropped in 101.14 leaves, while M4 sustained higher levels of this parameter [10,39]. Additional studies revealed that M4 significantly improved leaf gas exchange and leaf water status of scion under WD when grafted with different Vitis vinifera cultivars, as compared with other rootstocks, including SO4 and 1103 Paulsen [40,41]. Although the previous studies highlighted the value of M4 in improving vine tolerance to moderate-to-severe drought stress, the mechanisms underlying the superior performance of M4-grafted plants under water stress remain largely elusive.…”

How Do Novel M-Rootstock (Vitis Spp.) Genotypes Cope with Drought?

“…A recent study compared M4 to 1103P in grafting combination with Grechetto Gentile. The two combinations maintained similar water potential under water stress, though M4 showed higher photosynthesis and water use efficiency [ 56 ]. Galbignani et al [ 57 ] found higher Pn values and higher instantaneous WUE values in Sangiovese grafted on M4 than grafted on SO4 under moderately water-stressed conditions.…”

Modifications Induced by Rootstocks on Yield, Vigor and Nutritional Status on Vitis vinifera Cv Syrah under Hyper-Arid Conditions in Northern Chile

“…Grafting allows some grape grower control over important agronomic traits and provides flexibility in growing a particular scion or cultivar across diverse soil and environmental conditions [9]. Vine rootstocks are commonly characterized according to the vigor attributes conferred to the scion and are able to modify scion gas exchange, water use efficiency, and, by consequence, crop productivity [10,11]. Recent reports showed significant effects on technological parameters, organic acids, yeast assimilable nitrogen, and phenolic and volatile compounds in grapes and wines obtained from grafted and ungrafted vines [2,[12][13][14].…”