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.
Highlights
Global warming is making rapid and transformative changes in the traits associated with viticulture across the world [1]
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
It is well known that rootstocks can confer different vigor to the grafted scion [12,31]; in our study, though, vegetative growth parameters (Table S1) show that, albeit 1103P had a tendency to slightly push growth, no significant difference was found in vine leaf area at the end of the experiment, re-enforcing the reliability of single leaf readings
Summary
Global warming is making rapid and transformative changes in the traits associated with viticulture across the world [1]. The heightened severity and frequency of several summer-induced stresses exerted in the vineyard are one of the most common ramifications of warming trends [1]. They encompass the simultaneous emergence of heat and water stress in conjunction with excessive radiation loads, leading to necrosis and leaf photoinhibitions, a significant reduction in yields, spoilage of fruit quality, and, in young plantings, vineyard loss [1,6]. As well as selection programs, have witnessed slow progress in viticulture, as evidenced in a subdued rate of material released over the past century, the pressure associated with warming trends has resulted in the selection of genotypes that can possibly confer to the scion a higher tolerance to abiotic stresses
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