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Summary Under salinity, Vitis spp. rootstocks can mediate salt (NaCl) exclusion from grafted V. vinifera scions enabling higher grapevine yields and production of superior wines with lower salt content. Until now, the genetic and mechanistic elements controlling sodium (Na+) exclusion in grapevine were unknown. Using a cross between two Vitis interspecific hybrid rootstocks, we mapped a dominant quantitative trait locus (QTL) associated with leaf Na+ exclusion (NaE) under salinity stress. The NaE locus encodes six high-affinity potassium transporters (HKT). Transcript profiling and functional characterization in heterologous systems identified VisHKT1;1 as the best candidate gene for controlling leaf Na+ exclusion. We characterized four proteins encoded by unique VisHKT1;1 alleles from the parents, and revealed that the dominant HKT variants exhibit greater Na+ conductance with less rectification than the recessive variants. Mutagenesis of VisHKT1;1 and TaHKT1.5-D from bread wheat, demonstrated that charged amino acid residues in the eighth predicted transmembrane domain of HKT proteins reduces inward Na+ conductance, and causes inward rectification of Na+ transport. The origin of the recessive VisHKT1;1 alleles was traced to V. champinii and V. rupestris. We propose that the genetic and functional data presented here will assist with breeding Na+-tolerant grapevine rootstocks.

Background and Aims: Rootstocks influence the inorganic ion and organic acid composition of grapes of the scion variety. The aim was to investigate the impact of rootstocks on the inter-relationship of inorganic ions and organic acid anions in the skin and pulp of grapes and in resultant wine. Methods and Results: Vines were irrigated with water having electrical conductivities in the range 1.6–2.1 dS/m. Chloride, sodium, potassium, malic and tartaric acid concentrations were higher in almost all cases in skin than in pulp. Significant positive correlations existed between chloride and sodium concentrations in both pulp and skin. A significant negative linear regression existed between malic acid and both chloride and sodium concentrations in skin of Chardonnay berries. There were positive linear regressions in chloride concentration between berry (pulp and skin) and resultant wine chloride in both Chardonnay and Shiraz. Conclusion: The higher malic acid and lower chloride concentrations in skin of most grafted Chardonnay and Shiraz vines, and vice versa for own rooted vines, may indicate competition for similar transporter proteins involved in loading into skins. Alternatively, higher salt concentrations in skins may be associated with accelerated malic acid catabolism. Significance of the Study: Chloride-excluding rootstocks demonstrated advantages through reduced chloride (but not sodium) in pulp and skin of grape berries and in resultant wines. Where rootstocks reduced chloride concentrations in skin of grape berries, there is potential for higher malic acid in skin and in the resultant red wines.

Field-grown vines of cv. Sultana on either their own roots or grafted to a range of rootstocks, were drip-irrigated at one of three salinity levels (0.40, 1.75 and 3.50 dS/m) over a five year period. Rootstocks were Ramsey, 1103 Paulsen, J17-69 and 4 hybrids (designated R1, R2, R3 and R4) derived from parentage involving Vitis champini, V. berlandieri and V. vinifera. Grape juice total soluble solids, titratable acidity and pH were measured at harvest, while colour of dried fruit was measured before and after processing and again after six months storage. Damage index (an indicator of skin damage) was measured post-processing; sugar crystal formation in dried grapes and dried grape compaction were measured post-storage. There was a strong salinity x rootstock interaction for grape juice soluble solids concentration, soluble solids yield (the product of soluble solids concentration and fruit yield) and pH, but not for titratable acidity when analysed on the basis of 5 year means. Small increases (< 5%) in juice soluble solids concentration were recorded at medium salinity (1.75 dS/m) for the low vigour genotypes, Sultana on own-roots and on J17-69 rootstock, based on the 5 year means and Fisher's protected (interaction) LSDs. Moderate increases (< 10%) also occurred in years of low crop load e.g. 1993 at high salinity for the high vigour rootstock R2 and in 1995 at medium salinity for Sultana on own roots and at high salinity for Sultana on R1 rootstock. By contrast, decreases in soluble solids concentration occurred with increasing salinity for the high vigour rootstocks (Ramsey, 1103 Paulsen and R2) in years of high crop load e.g. 1992. Small (< 2%) increases in grape juice pH were recorded at high salinity for Sultana on R3 rootstock and moderate increases (< 7%) in grape juice titratable acidity were recorded at high salinity for Sultana on own roots and Sultana on J17-69, R1, R2 and R4 rootstocks. Dried grapes from all treatments achieved a light amber colour (quality grade termed 5 crown light) and were generally of high quality. Sultanas from own-rooted grapevines were redder (higher ‘a-value’) than sultanas from 1103 Paulsen and Ramsey when assessed as unprocessed fruit, after processing (both years) and after 6 weeks storage. While soluble solids yields per vine were 23–31% lower at high salinity for Sultana on own roots and on R1, R3 and R4 rootstocks, they were unaffected by high salinity for Ramsey, 1103 Paulsen and R2 rootstocks. Moreover, soluble solids yields for Sultana on Ramsey, 1103 Paulsen and R2 rootstocks were 1.4 to 2.5-fold higher than for Sultana on the other rootstocks at high salinity. This study has shown that over a 5 year period rootstocks such as Ramsey, 1103 Paulsen and R2 grafted with Sultana were tolerant of salinity, producing dried grapes of generally high quality.

This study was conducted over three seasons on irrigated Shiraz grapevines growing in a warm climate. We addressed The question of whether differences in berry size (within a population of berries from minimally pruned, own-rooted or Ramsey-grafted vines), would lead to differences in juice composition, wine composition or wine sensory score. Predictably, berry mass was found to increase with seed number, but berries in the smallest mass categories (0.3-0.7 g) still had similar juice soluble solids and pH; and similar concentrations of K+, tartaric acid and malic acid, compared with larger berries (1.4-2.0 g). Only by the very smallest mass category (0.3-0.55 g) was there any indication of better colour density (both by own-rooted and Ramsey-grafted vines) or higher anthocyanin concentration (for own-rooted vines) compared with larger berries (1.4-2.0 g). Concentrations of tartaric acid and K~ in berry skins were highest in the smallest berry mass categories (0.3-0.7 g( and decreased with increasing berry mass (up to 1.4-2.0 g). A strong correlation (R2 = 0.85 )between skin tartaric acid and K+ concentrations was observed across that range. Small-scale wine lost based on small berries (0.8-0.9 g) versus large berries (1.2-1.3 g) showed no differences in measures such as soluble solids, total acids or pH ob juice; nor any differences in pH, total acids, K+, tartrate, malate, spectral characteristics or sensory score of corresponding wines. Moreover, small berries had a similar skin to fruit ratio, and a similar juice yield, compared lo large berries. However, when measured post-fermentation, the ratio of seed weight to skin weight was higher for small berries. The mass range ob berries used here for small-scale winemaking (i.e. from 0.8-0.9 g up to 1.2-1.3 g), covered the range of Shiraz berry mass typically bound in irrigated vineyards (from 0.8 lo 1.5 g(, and thus confirms The relevance of present outcomes to practical winemaking. Finally, our data lot variation in juice and wine composition as a function of berry size, showed consistent trends for all seasons, and thus implies that reported instances of improved wine quality from small berries (often associated with certain pruning treatments nr deficit irrigation strategies), are more likely due to treatment effects that lead to small Fruit, rather than to intrinsic developmental differences between large and small berries

Field vines of cv. Sultana, grown either on their own roots, or grafted to a range of rootstocks, were drip-irrigated at three salinity levels (0.40, 1.75 and 3.50 dS/m) over a five-year period. Rootstocks comprised Ramsey, 1103 Paulsen, J17-69 and 4 hybrids (designated R1, R2, R3 and R4) derived from parentage involving Vitis champini, V. berlandieri and V. vinifera. Concentrations of Cl-, Na+, K+, Ca2+ and Mg2+ were measured in petioles at flowering, and in laminae and grape juice at harvest, in each year of the trial. Vines on all rootstocks accumulated less chloride in either petioles at flowering or in laminae and juice at harvest compared with vines on own roots at all salinity treatments. By inference, all rootstocks behaved as chloride excluders relative to the roots of own-rooted vines. 1103 Paulsen was the best chloride excluder based on lowest concentrations of accumulated Cl- in petioles, laminae and grape juice at high salinity. Sultana on R3 rootstock at high salinity accumulated more Na+ in both laminae and grape juice (at harvest) than did Sultana on own roots or on any of the other rootstocks. Laminae K+ at harvest time was reduced at high salinity in Sultana on own roots and on all rootstocks. Concentrations of both Cl- and Na+ in petioles at flowering and in laminae and grape juice at harvest showed no significant correlation with either yield (as kg of fresh grapes per vine) or vigour (as measured by fresh weight of one-year-old pruning wood per vine) for any salinity treatment. There was however, a strong positive correlation between yield and the subsequent weight of one-year-old pruning wood for all salinity treatments. There was also a negative correlation between Na+ concentrations in petioles at flowering and the subsequent weight of one year-old-pruning wood from the 0.40 dS/m treatment. Similar negative correlations were found between Na+ concentration in both laminae and grape juice at harvest time, and the subsequent weight of one-year-old pruning wood from the 0.40 dS/m treatment (but not from either the 1.75 or 3.50 dS/m treatments). Based on these findings and those from Walker et al. 2002a we conclude that a high innate vigour of a rootstock combined with moderate to high chloride and sodium exclusion ability represents the best combination for salt tolerance in Sultana grapevines as measured by yield at moderate to high salinity.

Background Salt tolerance in grapevine is associated with chloride (Cl−) exclusion from shoots; the rate-limiting step being the passage of Cl− between the root symplast and xylem apoplast. Despite an understanding of the physiological mechanism of Cl− exclusion in grapevine, the molecular identity of membrane proteins that control this process have remained elusive. To elucidate candidate genes likely to control Cl− exclusion, we compared the root transcriptomes of three Vitis spp. with contrasting shoot Cl− exclusion capacities using a custom microarray. Results When challenged with 50 mM Cl−, transcriptional changes of genotypes 140 Ruggeri (shoot Cl− excluding rootstock), K51-40 (shoot Cl− including rootstock) and Cabernet Sauvignon (intermediate shoot Cl− excluder) differed. The magnitude of salt-induced transcriptional changes in roots correlated with the amount of Cl− accumulated in shoots. Abiotic-stress responsive transcripts (e.g. heat shock proteins) were induced in 140 Ruggeri, respiratory transcripts were repressed in Cabernet Sauvignon, and the expression of hypersensitive response and ROS scavenging transcripts was altered in K51-40. Despite these differences, no obvious Cl− transporters were identified. However, under control conditions where differences in shoot Cl− exclusion between rootstocks were still significant, genes encoding putative ion channels SLAH3, ALMT1 and putative kinases SnRK2.6 and CPKs were differentially expressed between rootstocks, as were members of the NRT1 (NAXT1 and NRT1.4), and CLC families. Conclusions These results suggest that transcriptional events contributing to the Cl− exclusion mechanism in grapevine are not stress-inducible, but constitutively different between contrasting varieties. We have identified individual genes from large families known to have members with roles in anion transport in other plants, as likely candidates for controlling anion homeostasis and Cl− exclusion in Vitis species. We propose these genes as priority candidates for functional characterisation to determine their role in chloride transport in grapevine and other plants. Electronic supplementary material The online version of this article (doi:10.1186/s12870-014-0273-8) contains supplementary material, which is available to authorized users.

Shiraz grapevines on either their own roots, or on the rootstocks Ramsey, 1103 Paulsen, 140 Ruggeri or 101-14, were grown at two separate sites within the Murray-Darling viticultural region with similar irrigation regimes but with an irrigation water salinity of either 0.43 dS/m (low salinity site) or 2.3 dS/m (high salinity site). Rootstock effects on grape berry development, ion concentrations, soluble solids and acidity were followed during one season. Wines were also made and compared using spectral analysis and sensory evaluation. Rootstock effects that were common across both sites were (1) a close relationship between K+ and soluble solids accumulation in developing grape berries which commenced at the onset of veraison and was indicative of a link between K+ and sucrose transport in the phloem, and (2), higher wine K+, pH and colour hue for all rootstocks with one exception, namely 101-14 at high salinity where 101-14 responded similarly to own roots. Juice K+, pH and loss of K+ from juice during winemaking were highest for grapes from the high salinity site. Mean berry weight was smaller and the range in berry size across rootstocks was narrower at the saline site. The narrower range in berry sizes may have contributed to fewer rootstock effects on wine spectral characteristics at high salinity. There was no effect of rootstock on CO2 assimilation rate or stomatal conductance at either site, although intrinsic leaf-based water-use efficiency measured as A/g was 50% higher at the saline site. All treatments exhibited berry shrivel at maturity, but the extent was smaller at high salinity. Slower development of berry colour during veraison was observed on some rootstocks, for example 101-14, and while unrelated to canopy size per se, a higher leaf-to-fruit ratio for 101-14 may have been a factor. Slower berry colour development during veraison had no bearing on the colour density of wine made from the harvested grapes.

Salinity treatments of 0.43, 1.7 and 3.4 dS/m were applied through a drip‐irrigation system to four‐year‐old vines of own‐rooted Sultana (SO) and Sultana on Ramsey rootstock (Sr) The vines were planted in spring 1987 and established for two years under irrigation with low salinity (0.43 dS/m) water before commencing the range of salinity treatments in spring 1989. The effects of salinity and rootstock on yield, size and composition of berries, canopy size, lamina CO2 assimilation, leaf water relations and lamina ion concentrations were studied between veraison and harvest during the second season of salinity treatments. Mature leaves of SR had higher rates of CO2 assimilation (leaf area basis) and stomatal conductance than comparable leaves of SO. The high salinity treatment (3.4 dS/m) reduced CO2 assimilation rate of SO but not of SR. Medium salinity (1.7 dS/m) had no significant effect on CO2 assimilation rate of either type. Laminae of SO accumulated significantly higher concentrations of chloride than SR vines at all salinity levels. There was a significant negative correlation (r2= 0.44) between CO2 assimilation rate and laminae chloride of SO. Leaf sodium concentrations increased with increasing salinity, but concentrations in laminae at high salinity were similar in SO and SR, with SR showing no reduction in CO2 assimilation. Leaf potassium concentrations were higher in SR, but decreased with increasing salinity, whereas magnesium concentrations were similar in SO and SR vines but increased in both at high salinity. Leaf water potential and relative water content were not significantly affected by salinity in either SO or SR vines. Both vine types had reduced total leaf area and pruning wood weights as salinity increased, but they were greater in SR at all salinity levels because of the higher inherent capacity for biomass production in SR vines. The bigger canopies, lower lamina chloride concentrations and ‘normal’ photosynthesis rates of SR vines at 3.4 dS/m enabled these vines to mature crops with similar berry weights, sugar contents and fruit yield compared with those of SO vines at 0.43 dS/m. The research demonstrated the benefit of using Ramsey rootstock for Sultana under saline field conditions and provided a physiological explanation for their higher salt tolerance.

Plant cation-chloride cotransporters (CCCs) have been implicated in conferring salt tolerance. They are predicted to improve shoot salt exclusion by directly catalyzing the retrieval of sodium (Na(+)) and chloride (Cl(-)) ions from the root xylem. We investigated whether grapevine (Vitis vinifera [Vvi]) CCC has a role in salt tolerance by cloning and functionally characterizing the gene from the cultivar Cabernet Sauvignon. Amino acid sequence analysis revealed that VviCCC shares a high degree of similarity with other plant CCCs. A VviCCC-yellow fluorescent protein translational fusion protein localized to the Golgi and the trans-Golgi network and not the plasma membrane when expressed transiently in tobacco (Nicotiana benthamiana) leaves and Arabidopsis (Arabidopsis thaliana) mesophyll protoplasts. AtCCC-green fluorescent protein from Arabidopsis also localized to the Golgi and the trans-Golgi network. In Xenopus laevis oocytes, VviCCC targeted to the plasma membrane, where it catalyzed bumetanide-sensitive (36)Cl(-), (22)Na(+), and (86)Rb(+) uptake, suggesting that VviCCC (like AtCCC) belongs to the Na(+)-K(+)-2Cl(-) cotransporter class of CCCs. Expression of VviCCC in an Arabidopsis ccc knockout mutant abolished the mutant's stunted growth phenotypes and reduced shoot Cl(-) and Na(+) content to wild-type levels after growing plants in 50 mm NaCl. In grapevine roots, VviCCC transcript abundance was not regulated by Cl(-) treatment and was present at similar levels in both the root stele and cortex of three Vitis spp. genotypes that exhibit differential shoot salt exclusion. Our findings indicate that CCC function is conserved between grapevine and Arabidopsis, but neither protein is likely to directly mediate ion transfer with the xylem or have a direct role in salt tolerance.