Search

SUMMARY: The leaf of a deciduous species completes its life cycle in a few months. During leaf maturation, osmolyte accumulation leads to a significant reduction of the turgor loss point (ΨTLP), a known marker for stomatal closure. Here we exposed two grapevine cultivars to drought at three different times during the growing season to explore if the seasonal decrease in leaf ΨTLP influences the stomatal response to drought. The results showed a significant seasonal shift in the response of stomatal conductance to stem water potential (gs~Ψstem), demonstrating that grapevines become increasingly tolerant to low Ψstem as the season progresses in coordination with the decrease in ΨTLP. We also used the SurEau hydraulic model to demonstrate a direct link between osmotic adjustment and the plasticity of gs~Ψstem. To understand the possible advantages of gs~Ψstem plasticity, we incorporated a seasonally dynamic leaf osmotic potential into the model that simulated stomatal conductance under several water availabilities and climatic scenarios. The model demonstrated that a seasonally dynamic stomatal closure threshold results in trade‐offs: it reduces the time to turgor loss under sustained long‐term drought, but increases overall gas exchange particularly under seasonal shifts in temperature and stochastic water availability. A projected hotter future is expected to lower the increase in gas exchange that plants gain from the seasonal shift in gs~Ψstem. These findings show that accounting for dynamic stomatal regulation is critical for understanding drought tolerance. [ABSTRACT FROM AUTHOR]

• Deficit irrigation (35% ET 0) does not reduce stem water potential (Ψ stem) below water stress levels in Merlot Khorus. • Stomatal conductance (g s) and net photosynthesis (A N) are negatively affected by deficit irrigation in Merlot Khorus. • The basal crop coefficient (K cb) of Merlot Khorus in northeast Italy is far different from what suggested by standard methodologies. • Merlot Khorus is suitable for deficit irrigation management. Fungus–resistant varieties are gathering attention all over viticultural areas owing to their contribution to sustainable management. Sustainable viticulture implies lower inputs in terms of pesticides and water. However, investigations on the physiological behavior of fungus–resistant varieties under drought stress have been seldom conducted so far. Under climate change conditions, evaluating precise water use is particularly important to set up proper irrigation. In this study, a two-year experiment was imposed to characterize the physiological behavior of the fungus–resistant variety Merlot Khorus under two contrasting water regimes (full irrigation, WW; water deficit, WD). Berry weight and grape quality in the two treatments was also compared to evaluate the feasibility of adopting deficit irrigation strategies in the region. The study was conducted in the Friuli Venezia Giulia region (Italy). The measured values of stem water potential (Ψ stem) did not highlight any severe water stress (> -1.15 MPa) in WD. However, g s and A N decreased to values typical of drought–stressed vines. Concurrently, the experiment assessed that the calculated Kcb of Merlot Khorus in northeast Italy is far different from what has been suggested by standard methodologies and the literature. The grapes under deficit irrigation showed reduced berry weight, while basic maturation parameters and anthocyanins were improved. Overall, the study indicated that Merlot Khorus appears to be a genotype suitable for dry farming or deficit irrigation management in northeastern Italy. Therefore, the results may help winegrowers to improve irrigation strategies. [ABSTRACT FROM AUTHOR]

Grapevines in Karst between Italy and Slovenia are grown on a shallow "Terrarossa" red karst loam laying on carbonate rocks. In Karst, water stress conditions occur during the summer season both because of the rain scarcity and the poor available water content of the soils. Moreover, irrigation can be used to only partially supply grapevine requirements, where possible. An irrigation trial was carried out in a vineyard of "Refošk" during the seasons 2018–2019 to understand the effects of two deficit irrigation regimes (20% and 50% ET C) on yield parameters and basic maturation, but mainly on polyphenol content, composition and extractability. During the summer season Ψ stem was regularly checked in order to follow the plant water status, and at harvest time berry samples were collected to determine the total concentration of anthocyanins and proanthocyanidins and their extractability in a wine-like solution. Moreover, the structural characteristics of seed and skin proanthocyanidins were analyzed. In both seasons, differences in plant water status were ascertained, but values of Ψ stem never highlighted situations of severe water stress for both deficit irrigation regimes. 20% ET C resulted in a significant increase in the concentration of both total and extractable anthocyanins; on the other hand, proanthocyanidin concentration was not significantly affected by the irrigation regime. As regards the structure of proanthocyanidins, 20% ET C accounted for a higher degree of galloylation in both total and extractable seed and skin proanthocyanidins. A more limited irrigation regime resulted in both higher anthocyanin concentration and degree of galloylation of seed and skin proanthocyanidins - attributes that might account for a better wine quality potential. • Berry weight and seed color were significantly impacted by water regime. • The most limited water deficit (20% ETc) increased anthocyanins while reduced soluble solids in grapes. • 20% ETc and 50% Etc irrigation regimes showed no differences in grape proanthocyanidin concentration. • Galloylation of skin and seed proanthocyanidins was higher with 20% ETc than with 50% ETc. [ABSTRACT FROM AUTHOR]

Disentangling the factors that foster the tolerance to water stress in plants could provide great benefits to crop productions. In a two-year experiment, two new PIWI (fungus resistant) grapevine varieties, namely Merlot Kanthus and Sauvignon Kretos (Vitis hybrids), grown in the field, were subjected to two different water regimes: weekly irrigated (IR) or not irrigated (NIR) for two months during the summer. The two varieties exhibited large differences in terms of performance under water-limiting conditions. In particular, Merlot Kanthus strongly decreased stem water potential (Ψ s) under water shortage and Sauvignon Kretos maintained higher Ψ s values accompanied by generally high stomatal conductance and net carbon assimilation, regardless of the treatment. We hypothesized differences in the hormonal profile that mediate most of the plant responses to stresses or in the regulation of the aquaporins that control the water transport in the leaves. In general, substantial differences were found in the abundance of different hormonal classes, with Merlot Kanthus reporting higher concentrations of cytokinins while Sauvignon Kretos higher concentrations of auxins, jasmonate and salicylic acid. Interestingly, under water stress conditions ABA modulation appeared similar between the two cultivars, while other hormones were differently modulated between the two varieties. Regarding the expression of aquaporin encoding genes, Merlot Kanthus showed a significant downregulation of VvPIP2;1 and VvTIP2;1 in leaves exposed to water stress. Both genes have probably a role in influencing leaf conductance, and VvTIP2;1 has been correlated with stomatal conductance values. This evidence suggests that the two PIWI varieties are characterized by different behaviour in response to drought. Furthermore, the findings of the study may be generalized, suggesting the involvement of a complex hormonal cross-talk and aquaporins in effectively influencing plant performance under water shortage. • Sauvignon Kretos exhibited higher Ψ s even in the presence of water shortage. • The observed different degree of tolerance is probably ABA independent. • Sauvignon Kretos hormonal profile is more suitable to cope with water limiting conditions. • VvPIP2;1 and VvTIP2;1 aquaporins might affect the hydraulic behaviour under water stress. [ABSTRACT FROM AUTHOR]

Phytoplasmas are sieve-elements restricted wall-less, pleomorphic pathogenic microorganisms causing devastating damage to over 700 plant species worldwide. The invasion of sieve elements by phytoplasmas has several consequences on nutrient transport and metabolism, anyway studies about changes of the mineral-nutrient profile following phytoplasma infections are scarce and offer contrasting results. Here, we examined changes in macro- and micronutrient concentration in tomato plant upon ' Candidatus Phytoplasma solani' infection. To investigate possible effects of ' Ca. P. solani' infection on mineral element allocation, the mineral elements were separately analysed in leaf midrib, leaf lamina and root. Moreover, we focused our analysis on the transcriptional regulation of genes encoding trans-membrane transporters of mineral nutrients. To this aim, a manually curated inventory of differentially expressed genes encoding transporters in tomato leaf midribs was mined from the transcriptional profile of healthy and infected tomato leaf midribs. Results highlighted changes in ion homeostasis in the host plant, and significant modulations at transcriptional level of genes encoding ion transporters and channels. • Invasion of sieve elements by phytoplasma affects nutrient transport and metabolism. • Macro- and micronutrients such as K+, Ca2+, Mg2+, Fe2+ and Mn2+ change in concentration upon infection in tomato plants. • Infected tomato plants up- and downregulate in the leaf midrib many transmembrane transporters. • We provide a manually curated inventory of 200 genes encoding transporters regulated in the midrib upon infection. [ABSTRACT FROM AUTHOR]

Grapevines are being challenged by climate changes, forcing winemakers to implement irrigation systems to cope with excessive water stress. Previous studies focused on a small set of international varieties, and only few data are available for terroirs hosting cultivars with possibly different responses to drought stress. In this light, we monitored grapevine water status and grape's physical and chemical composition, as well as concentration and structural characteristics of grape extractable polyphenols, in ten different Refošk vineyards located in the Classical Karst terroir during 2018 and 2019. Grapevines did not suffer severe stress during the two years, but their response to water shortage periods was highly heterogeneous, as pre-dawn (Ψ pd) and minimum (Ψ min) leaf water potential significantly differed between vineyards, especially during the drier part of the season. Moreover, the timing of maximum water stress differed in the two years, as in 2019 longer water shortage periods and higher temperature occurred at flowering stage and before veraison, while in 2018 they were higher after veraison. These differences influenced berry's quality, as titratable and malic acid concentration in juice, as well as total anthocyanin, total polyphenols and higher high molecular weight proanthocyanidins (HMWP) concentration in skins, were higher in 2019 than in 2018. Regarding seed proanthocyanidins, HMWP concentration, mean degree of polymerisation (mDP) and percentage of galloylation (G) in seeds were higher in 2018 than in 2019. The differences in water status measured in spatially close-related vineyards strongly support the importance of monitoring grapevines' water status dynamics to design adequate and effective water management activities rather than relying on climate data solely. Moreover, the timing of water shortage periods also played a role in determining Refošk grape quality. Our analyses showed that the higher (but still moderate, with Ψ pd and Ψ min mean values around −0.50 and −1.25 MPa, respectively) water stress between veraison and harvest occurred in 2018 might reduce Refošk grape acidity and increase concentration, polymerisation and galloylation of seed extractable proanthocyanidins. • Climate change is forcing winemakers to implement irrigation systems in Karst. • Water status affects grape quality, but this relationship is poorly understood. • High heterogeneity in water status was found in spatially closed vineyards. • Different timing of water shortage in 2018 and 2019 influenced berry's quality. • Water management activities should be planned based on actual plant water needs. [ABSTRACT FROM AUTHOR]