Ungrafted Grapevines Research Articles

The effects of mixes of peat and olive pomace at various ratios on the vegetative growth of potted grapevine saplings

Numerous studies have been conducted in order to utilize the olive pomace, the solid waste left over from the oil processing of olives, which is widely cultivated, especially in Mediterranean countries, and to consider it a raw material that has added value instead of being considered waste. Some of these research are focused on establishing the re-utilization of olive pomace in agricultural production. Although some studies have reported that olive pomace can be utilized as fertilizer, soil improvement regulator, solid media culture, and even mulching material, this study was carried out due to the lack of sufficient scientific data on whether or not this material can be used as a growth medium in the cultivation of potted grapevine saplings. The study was carried out by growing ungrafted grapevine saplings of Vitis vinifera L. cv. Hatun Parmağı on media with peat and olive pomace at different ratios for six months, and then some vegetative growth parameters were examined. Due to the elevated olive pomace ratios in the growth medium, shoot and root growth of the grapevine saplings were restricted. The chlorophyll index and root fresh weight decreased dramatically when more than 25% (v/v) and 20% (v/v) crude pomace were available in the growth medium, respectively. Moreover, the availability of olive pomace in the medium significantly reduced shoot length, number of leaves, shoot weight, and leaf weight of grapevine saplings, regardless of the amount of olive pomace. However, it was found that 15% (v/v) or less of crude olive pomace could be utilized in growth medium mixtures when growing potted grapevine saplings; however, higher ratios would prevent the saplings from attaining marketable quality. While designing new studies, examining different grape varieties, fruit species, and lower olive pomace ratios would contribute to new and more comprehensive findings on the utilization of olive pomace in growing potted saplings.

The activation of iron deficiency responses of grapevine rootstocks is dependent to the availability of the nitrogen forms

BackgroundIn viticulture, iron (Fe) chlorosis is a common abiotic stress that impairs plant development and leads to yield and quality losses. Under low availability of the metal, the applied N form (nitrate and ammonium) can play a role in promoting or mitigating Fe deficiency stresses. However, the processes involved are not clear in grapevine. Therefore, the aim of this study was to investigate the response of two grapevine rootstocks to the interaction between N forms and Fe uptake. This process was evaluated in a hydroponic experiment using two ungrafted grapevine rootstocks Fercal (Vitis berlandieri x V. vinifera) tolerant to deficiency induced Fe chlorosis and Couderc 3309 (V. riparia x V. rupestris) susceptible to deficiency induced Fe chlorosis.ResultsThe results could differentiate Fe deficiency effects, N-forms effects, and rootstock effects. Interveinal chlorosis of young leaves appeared earlier on 3309 C from the second week of treatment with NO3−/NH4+ (1:0)/-Fe, while Fercal leaves showed less severe symptoms after four weeks of treatment, corresponding to decreased chlorophyll concentrations lowered by 75% in 3309 C and 57% in Fercal. Ferric chelate reductase (FCR) activity was by trend enhanced under Fe deficiency in Fercal with both N combinations, whereas 3309 C showed an increase in FCR activity under Fe deficiency only with NO3−/NH4+ (1:1) treatment. With the transcriptome analysis, Gene Ontology (GO) revealed multiple biological processes and molecular functions that were significantly regulated in grapevine rootstocks under Fe-deficient conditions, with more genes regulated in Fercal responses, especially when both forms of N were supplied. Furthermore, the expression of genes involved in the auxin and abscisic acid metabolic pathways was markedly increased by the equal supply of both forms of N under Fe deficiency conditions. In addition, changes in the expression of genes related to Fe uptake, regulation, and transport reflected the different responses of the two grapevine rootstocks to different N forms.ConclusionsResults show a clear contribution of N forms to the response of the two grapevine rootstocks under Fe deficiency, highlighting the importance of providing both N forms (nitrate and ammonium) in an appropriate ratio in order to ease the rootstock responses to Fe deficiency.

Anthocyanin Accumulation and Its Corresponding Gene Expression, Total Phenol, Antioxidant Capacity, and Fruit Quality of ‘Crimson Seedless’ Grapevine (Vitis vinifera L.) in Response to Grafting and Pre-Harvest Applications

The color of grapevine berries is one of the most important quality parameters that define the appearance, attracts the consumer, and determines the price, especially in red grape cultivars. Some grape varieties show less color development due to many factors such as temperature, light intensity, and agricultural management. The present study aimed to evaluate diverse phytohormones coupled with grafting on quality and fruit coloration of ’Crimson Seedless‘ grapes. Pre-harvest foliar treatments of abscisic acid (ABA) at 400 mg L−1, methyl jasmonate (MeJ) at 1 mM L−1, ethephon (Eth) at 480 mg L−1, and melatonin (Mel) at 100 μmol were applied after 7 days and repeated after 21 days of ‘Veraison’ (beginning of the coloring phase). The results exposed that the ABA application provided the best anthocyanin accumulation with grafted grapevines whereas Eth displayed the maximum anthocyanin accumulation with ungrafted grapevines. Moreover, the expression of anthocyanin biosynthesis genes (chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), and flavanol 3-O-glucosyl transferase (UFGT)) was consistent with the anthocyanin concentration in berry peel. Moreover, Eth treatment revealed the highest total phenols and antioxidant capacity for both grafted and ungrafted grapevines. MeJ phytohormone exhibited the largest total yield, whereas the treatment of Eth increased the weight of 50 berries and the bunch. Furthermore, ABA induced the uppermost firmness and removal force. Regarding the chemical attributes, the Mel treatment revealed the minimum value of titratable acidity (TA) and the highest polyphenol oxidase (PPO) activity, while the MeJ treatment recorded the superior soluble solids content (SSC), in addition to phenylalanine ammonia-lyase (PAL) and catalase (CAT) enzymes activities. Eth treatment produced the highest activity of the peroxidase (POD) enzyme. Finally, the grafting treatment improved most of the studied fruit attributes.

Effect of drought on aquaporin expression in grafted and ungrafted grapevine cultivars

Drought stress severely affects growth, development and productivity in most agricultural crops. Since ancient times, rootstocks have been used to enable crop cultivation in unsuitable soil conditions. In the present study, three factors were evaluated: 1) cultivar: Vitis vinifera L. cv. ‘Horozkarası’ (drought-tolerant) and cv. ‘Kabarcık’ (drought-sensitive) were used; 2) rootstock: each cultivar was self-rooted and grafted onto ‘Rupestris du Lot’ rootstock; 3) drought stress: half of each cultivar/rootstock combination underwent drought stress and the other half was irrigated at field capacity for seven days. In order to estimate the responses of the cultivars, relative water content, proline content and aquaporin isoform expression levels (VvPIP2;1, VvPIP2;2, VvTIP1;1, and VvTIP2;1) were quantified. The results revealed that drought stress caused more reduction in relative water content (RWC) in ‘Kabarcık’ cultivar (drought-sensitive) than in ‘Horozkarası’ cultivar (drought-tolerant). Proline content increased in both cultivars in response to drought stress but to a relatively greater extent in the grafted ‘Kabarcık’ cultivar. Considering expression levels of genes, VvPIP2;1, VvPIP2;2, and VvTIP2;1 were downregulated whilst VvTIP1;1 was upregulated in the leaf. Both ‘Horozkarası’ and ‘Kabarcık’ cultivars showed similar trends in terms of their responses to drought stress. Grafting significantly increased the proline content in both cultivars exposed to drought stress. The rootstock conferred better drought protection to ‘Kabarcık’ cultivar than to ‘Horozkarası’ cultivar.

Rootstocks Shape Their Microbiome-Bacterial Communities in the Rhizosphere of Different Grapevine Rootstocks.

The microbiota associated with the rhizosphere is responsible for crucial processes. Understanding how the plant and its bacterial community interact is of great importance to face the upcoming agricultural and viticultural challenges. The composition of the bacterial communities associated with the rhizosphere of grapevines is the result of the interaction between many drivers: biogeography, edaphic factors, soil management and plant genotype. The experimental design of this study aimed to reduce the variability resulting from all factors except the genotype of the rootstock. This was made possible by investigating four ungrafted grapevine rootstock varieties of the same age, grown on the same soil under the same climatic conditions and managed identically. The bacterial communities associated with the rhizosphere of the rootstocks 1103 Paulsen, 140 Ruggeri, 161-49 Couderc and Kober 5BB were characterized with the amplicon based sequencing technique, targeting regions V4–V5 of 16S rRNA gene. Linear discriminant analysis effect Size (LEfSe) analysis was performed to determine differential abundant taxa. The four rootstocks showed similarities concerning the structure of the bacteria assemblage (richness and evenness). Nonetheless, differences were detected in the composition of the bacterial communities. Indeed, all investigated rootstocks recruited communities with distinguishable traits, thus confirming the role of rootstock genotype as driver of the bacteria composition.

“Bois noir” incidence reduction by grafting recovered grapevine shoots

It was evaluated if grafting of recovered material on symptomatic and symptomless grapevines can have curative and preventive effects against the “bois noir” phytoplasma disease. Symptom observation and molecular detection of ‘Candidatus Phytoplasma solani’ were conducted on grafted and ungrafted grapevines. The percentage of symptomatic and infected plants was significantly reduced in grafted symptomatic grapevine, indicating that grafting of recovered shoots may have a curative effect.

Changes in Morphological, Physiological Traits and Enzyme Activity of Grafted and Ungrafted Grapevine Rootstocks Under Drought Stress

American grapevine rootstocks are used as the most efficient control method for phylloxera disease. Vitis vinifera species are grown over these rootstocks. The rootstocks may have different drought tolerances. In present study, morphological and physiological responds and enzyme activities of grafted and ungrafted grapevines were investigated under drought stress. The rootstocks Rupestris du Lot, 420A, 5BB, SO4, 8B, 110R, 1103P, 140Ruggeri and Ramsey and K‑7 clone of Sultani Seedless grape cultivar were used as the plant material of this study. Drought stress was exerted as water deficits and stress treatments were terminated when the available moisture level dropped to 5%. Current findings revealed that grafted plants were less influenced morphologically from the droughts than the ungrafted ones. In control group, average leaf water potential was measured as −0.51 MPa for ungrafted plants and −0.46 MPa for grafted plants. In stress group, leaf water potential was measured as −2.03 MPa for ungrafted plants and as −1.69 MPa for grafted ones. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzyme activities of both grafted and ungrafted plants increased with drought stress. Considering the enzyme activities of ungrafted plants in control and stress groups, it was observed that SOD activity increased from 508 (unit/mg protein) to 852 (unit/mg protein); APX activity increased from 153 (micromole/mg protein/min) to 584 (micromole/mg protein/min). In grafted plants, SOD activity increased from 639 (unit/mg protein) to 796 (unit/mg protein); APX activity increased from 414 (micromole/mg protein/min) to 1002 (micromole/mg protein/min). The drought resistant rootstocks (like 140Ru, 110R) exhibited higher enzyme activity in both control and stress groups than drought sensitive rootstocks (like 5BB, SO4).

Gas Exchange Relations of Ungrafted Grapevines (cv. Carménère) Growing Under Irrigated Field Conditions

A study was carried out to evaluate the leaf gas exchange relations and water-use efficiency (WUE) of ungrafted Carmenere (Vitis vinifera L.) grapevines growing under field conditions and different levels of water stress. Stomatal conductance (g s ), transpiration (E), net CO 2 assimilation (A N ) and stem water potential (Ψs) were measured at midday in a drip-irrigated commercial vineyard located in the Maule Valley (Chile) during three growing seasons (2005 to 2009). In addition, the instantaneous (A N /E) and intrinsic (A N /g s ) water-use efficiencies and stomatal sensitivity factor (k) were estimated for the own-rooted grapevines. In this study a significant non-linear relationship was observed between A N and g s (r 2 = 0.82), with values of A N decreasing from 14.9 to 3.5 μmol/m 2/ sec as g s diminished from 0.5 to 0.05 mol/m 2 /sec. This resulted in a progressive increase in WUEi (intrinsic water use efficiency). A significant linear relationship was observed between Ψs and g s (r 2 = 0.39) for measurements taken before and after veraison, with an increasing scattering from -1.6 to -0.4 MPa. Finally, k decreased as water stress increased, with values of 234 and 120 for no and severe water stress respectively, while k ranged from 264 to 480 and 255 to 297 for the measurements taken before and after veraison respectively. Based on the results obtained in the present study, the cultivar Carmenere could be classified as drought tolerant at low water potentials, with a large range of physiological parameters changing in response to water stress.

Aquaporins isoforms in cv. Touriga Nacional grapevine under water stress and recovery—Regulation of expression in leaves and roots

The aim of this work was to advance the knowledge in aquaporins expression and physiological responses of Touriga Nacional grapevine to water stress and recovery. Ungrafted grapevines cv. Touriga Nacional were subjected to two different irrigation treatments: (i) a well watered treatment (WW), in which vines were daily irrigated, being maintained at field capacity; (ii) and a water stress treatment (WS), in which vines were not irrigated along six days, with a later recovery (Rec), with these vines being re-irrigated at field capacity. Measurements started 48h after treatments application (T1, mild stress), and from this point on, every 48h until the maximum water stress point was reached (144h after the beginning of the trial, T2). After this point WS plants were re-watered, and 48h after this recovery, measurements were taken again in both treatments. The expression pattern of different aquaporins (VvPIP2;1–VvTIP1;1–VvTIP2;1–VvTIP2;2 and VvSIP) was studied in roots and leaves in both treatments at T1, T2 and Rec respectively. With the same periodicity, leaf and root specific hydraulic conductivity (Ks-leaf; Ks-root), abscisic acid (ABA) concentration, xylem sieve pH and leaf temperature were assessed. Both VvPIP2;1 and VvTIP2;2 were down regulated in WS roots, which was in line with the decrease observed in Ks-root. However, non-significant effects on Ks-leaf were observed in WS, in parallel with an up-regulation of VvPIP2;1 and VvTIP1;1. An increase of ABA in roots and leaves of WS vines was observed, in line with the results of vine water status, leaf temperature and pH of xylem sieve. Overall, results demonstrate the existence of different regulatory mechanisms occurring in response to water stress, being dependent on stress intensity and plant organ.

Cultural Conditions and Propagule Type Influence Relative Chloride Exclusion in Grapevine Rootstocks

Breeding for salt resistance in grapevines and other crops has made slow progress despite decades of research. One factor contributing to this problem in grapevines is the weak or nonexistent correlation of field and greenhouse performance observed in some studies when salt resistance is assessed by chloride accumulation in leaf tissue. To develop a rapid chloride exclusion assay for use in rootstock breeding, multiple systems were tested. Results were obtained wherein the well-established field performance of specific genotypes was augmented, equalized, or reversed when in containerized culture. One assay using fritted clay media and herbaceous cuttings yielded a rank order and relative chloride uptake among the tested genotypes that was similar to published values from long-term studies in experimental vineyards. This assay used only 14 days of high salt exposure, was inexpensive, required relatively little space and maintenance, and has continued to provide reliable data in subsequent experiments. The results demonstrate the potential for considerable plasticity in chloride exclusion exhibited by ungrafted grapevines when assayed in containers. This underscores the importance of system design wherein genotypes of known capacity for chloride exclusion are accurately calibrated to their established field performance. This study describes an empirically derived assay that replicates these conditions closely enough to be used in a rootstock breeding program for improved chloride exclusion.

Influence of Green Algae Chlorella vulgaris on Infested with Xiphinema index Grape Seedlings

Plant-parasitic nematodes are considered a major pest in grape growing countries. The present study was conducted during June-November 2007. The aim of the pot experiments was to establish the impact of dry extract of Chlorella vulgaris on the ungrafted grapevine seedlings cv.“Palieri” infested with root ectoparasite Xiphinema index. Different dosages of Chlorella (0.5, 1.0, 2,0 g per plant/pot) were investigated. The results show a decrease in the number of X. index in the variants treated with 1g Chlorella. There has been a positive effect on the growth characteristics of the test plants at the same concentrations. The green algae Chlorella vulgaris as a powerful phytoprotector have strong stimulating effect on the plant growth.

Screening of rhizosphere bacteria from grapevine for their suppressive effect on Xiphinema index Thorne & Allen on in vitro grape plants

Xiphinema index is the most aggressive root parasite affecting vines in Chile, controlled mainly chemically. The aim of this study was to identify rhizobacteria in grapevine roots growing in infested soils and to determine if some of these affect the parasitism caused by the nematode. Rhizobacteria of ungrafted grapevine cultivars from 11 vineyards were isolated using TSBA and identified with FAMEs analysis. The antagonistic effect to X. index of those from soils 1 to 4 was assessed in 500 ml pots treating 2 months old in vitro plants with a bacterial suspension containing 1 × 106 c.f.u./ml and 400 nematodes, determining after 4 months growth nematode populations and root damages. Also culture filtrates were assessed. 400 isolates in 25 genera were obtained from the 11 vineyards. The most frequent species were Pseudomonas putida (35.1%), Escherichia coli (7.6%) and Pseudomonas fluorescens (6.1%). Isolates of soils 1 to 4, show that Bacillus megaterium, B. brevis, Pseudomonas corrugata, P. savastanoi, Stenotrophomonas maltophilia and Serratia plymuthica reduced root damage and suppressed populations, meanwhile strains of B. brevis and Comamonas acidovorans increased plant growth but did not control nematodes. It is concluded that these isolates may be useful in biological control programmes in vineyards.

Influence of composted green waste on the population dynamics and dispersal of grapevine phylloxera Daktulosphaira vitifoliae

A field study was conducted, over three grapevine growing seasons, to assess the effect of composted green waste on the population dynamics and risk of dispersal of root-feeding grapevine phylloxera Daktulosphaira vitifoliae on ungrafted Vitis vinifera grapevines. An assessment was also made to determine the effect of compost application on grapevine vigour, grape yield and quality. Phylloxera crawler (first instar) emergence above-ground was significantly increased through the annual application of composted green waste. The implications of these results for phylloxera management on ungrafted grapevines are discussed.

Occurrence of Phaeomoniella chlamydospora and Phaeoacremonium aleophilum associated with Petri disease and esca in Australian grapevines

Over a 5-year period (1998–2002), 124 samples of diseased grapevines sent to the Department of Primary Industries, Knoxfield, in Victoria were diagnosed with the grapevine decline diseases, Petri disease and esca. The proportion of grapevines with Petri disease (82%) was much greater than those with esca (18%). In addition, Phaeomoniella chlamydospora was isolated from all but two of the samples, whereas Phaeoacremonium aleophilum was isolated from only 19 samples. Other fungi associated with grapevine decline diseases, such as species of Phomopsis, Cylindrocarpon, Botryosphaeria and heart-rotting basidiomycetes, were also isolated but not consistently. Thirty-two different grapevine cultivars were represented, and samples were received from most major grape-growing regions of New South Wales, South Australia, Victoria and Western Australia. The majority (62%) were ungrafted grapevines. Phaeomoniella chlamydospora was also found to be present in grapevines with no external symptoms of disease, including mother grapevines used for propagation.

Determination of transpiration in irrigated grapevines: comparison of the heat-pulse technique with gravimetric and micrometeorological methods

The use of a heat-pulse technique to monitor sap flow from which transpiration can be deduced was evaluated in ungrafted grapevines (Vitis vinifera L., cv. Sultana) under glasshouse and field conditions. There was a significant degree of agreement between daily transpiration deduced from heat-pulse velocity (T hp) and that determined directly by gravimetry in the glasshouse and by calibration using the Penman-Monteith equation in the field. Comparison throughout the growing season of T hp to transpiration calculated with the full Penman-Monteith equation produced a high coefficient of determination (r 2=0.69). A similar comparison of T hp with transpiration calculated with only the aerodynamic component of the Penman-Monteith equation produced a non-linear relationship, due to the equation over-estimating transpiration relative to T hp at high vapour pressure deficits (i.e. above 2.5 kPa). Values for total seasonal transpiration measured with heat-pulse sensors or calculated with either the full Penman-Monteith equation or with only the modified aerodynamic component of the equation were within 10% of each other. Transpiration (T hp) in grapevines with an adequate supply of soil water was shown to be coupled to ambient air conditions.

Chlorosis occurrence, natural arbuscular‐mycorrhizal infection and stilbene root concentration of ungrafted grapevine rootstocks growing on calcareous soil

Ungrafted rootstocks of fifteen grapevine genotypes with considerable resistance and susceptibility to lime‐tolerance [iron (Fe) deficiency chlorosis] were grown outdoors in pots with a fine, mixed (calcareous) mesic Typic Ustorthents soil, to determine the correlation between degree of lime‐tolerance, natural arbuscular mycorrhizal (AM) infection, and AM infection relationship with root levels of stilbenes (antifungal compounds). During the second year of growth, shoot length was measured and degree of chlorosis symptoms was evaluated four times as SPAD readings. At the end of the growing season, shoot and root dry weight, root length, AM infection, root concentration of stilbene compounds (trans‐ and cis‐resvaratrol, ϵ‐viniferin, pterostilbene) were determined. The most significant findings were: a) a negative correlation between degree of chlorosis and natural AM infection (expressed as total length of infected roots per plant); b) no significant correlation between AM infection and root stilbene concentration for the different rootstocks; c) positive relationship between chlorophyll leaf concentration and root dry weight, and d) a negative correlation between ϵ‐viniferin root level and shoot dry matter.

Water stress and rootstock influence on leaf gas exchange of grafted and ungrafted grapevines

In order to investigate the effects of rootstocks on plants of the genus Vitis subjected to gradually increased levels of water stress we studied the links between abscisic acid in leaves and the major leaf physiological parameters. Cuttings of Vitis vinifera cv. Müller Thurgau were grafted onto three hybrid rootstocks (H1, H8, H26) and grown in pots. Own-rooted plants of V. vinifera and own-rooted hybrids were also cultivated in an identical manner. Vines were tested during 7 and 14 days of water stress (i.e. daily water supply reduced to 66% of well-watered plants). Water stress reduced net photosynthesis and stomatal conductance with large differences between grafted and ungrafted vines. Significant differences were observed after only 14 days of water stress. In particular two grafting combinations, V. vinifera grafted on H1 (V/H1) and H8 (V/H8), did not show net photosynthesis reduction after 14 days of water stress. Water use efficiency increased with water stress whereas carboxylation efficiency was reduced. Net photosynthesis, stomatal conductance and carboxylation efficiency were affected by the rootstock genotype combination, so that under water stress only some rootstock genotypes transferred drought tolerance to the scion. Abscisic acid in leaves increased significantly from Control to 7 and 14 days of water stress but the relations with CO 2 assimilation rate, stomatal conductance and carboxylation efficiency appeared to be affected by the genotype of the vegetative apparatus. Our data show that the interaction between scion and rootstock with regard to production performance under water deficits may be an important consideration in vineyard planting strategies.

Uptake and distribution of potassium by grapevine rootstocks and its implication for grape juice pH of scion varieties

Differences in petiole K+ concentration of ungrafted grapevine rootstocks grown under field conditions at Merbein, Victoria, were compared with the rootstock effects on grape juice pH of the scion varieties Chardonnay and Ruby Cabernet. Significant positive correlations were obtained between grape juice pH of the scion varieties on various rootstocks and K+ accumulation in the petioles of ungrafted rootstock vines. Rootstock varieties that contributed to high pH in the grape juice of the scion (e.g. Freedom, Dog Ridge, Rupestris du Lot) showed high K+ concentrations in their petioles, while those rootstocks that contributed to low pH in the grape juice of the scion (e.g. 140 Ruggeri, 1202 Couderc, 110 Richter), had low K+ concentrations in their petioles. In 2 water culture experiments in the glasshouse, K+ uptake and distribution in ungrafted rootstock vines was examined at different K+ levels. In the first experiment the rootstocks 140 Ruggeri and Freedom had similar K+ concentrations in the various plant parts when grown in nutrient solution with 0.1 mmol K+/L. With K+ concentrations of 1, 2, and 10 mmol/L in the nutrient solution Freedom had significantly higher K+ contents in leaves and petioles than 140 Ruggeri. When K+ supply was increased from 1 to 2 mmol/L, K+ concentrations in the various plant parts were not significantly increased. However, when the supply was increased to 10 mmol/L, K t concentrations were significantly different. In the second experiment with K+ levels of 1 and 10 mmol/L, higher K+ contents were obtained in the basal and apical leaves of Dog Ridge and Ramsey compared with 140 Ruggeri, Schwarzmann, 1103 Paulsen and Sultana, while in roots, 140 Ruggeri, 110 Richter and Sultana had the highest K+ contents. Dog Ridge and Rarnsey are both known to increase scion grape juice K+ concentration and pH of the scion variety, while 140 Ruggeri and 1103 Paulsen contribute to low grape juice K+ concentration and pH. The results demonstrate that differences between rootstocks in the extent of K+ accumulation in the shoot are a major determinant of the rootstock effects on grape juice pH. The extent of K+ accumulation can best be measured in basal leaves or petioles. This provides a screening method for the evaluation of rootstocks which restrict K+ accumulation and contribute to lower grape juice pH.