Monoterpenols serve various biological functions and accumulate in grape (Vitis vinifera), where a major fraction occurs as nonvolatile glycosides. We have screened the grape genome for sequences with similarity to terpene URIDINE DIPHOSPHATE GLYCOSYLTRANSFERASES (UGTs) from Arabidopsis (Arabidopsis thaliana). A ripening-related expression pattern was shown for three candidates by spatial and temporal expression analyses in five grape cultivars. Transcript accumulation correlated with the production of monoterpenyl b-D-glucosides in grape exocarp during ripening and was low in vegetative tissue. Targeted functional screening of the recombinant UGTs for their biological substrates was performed by activity-based metabolite profiling (ABMP) employing a physiologic library of aglycones built from glycosides isolated from grape. This approach led to the identification of two UDP-glucose:monoterpenol b-D-glucosyltransferases. Whereas VvGT14a glucosylated geraniol, R,S-citronellol, and nerol with similar efficiency, the three allelic forms VvGT15a, VvGT15b, and VvGT15c preferred geraniol over nerol. Kinetic resolution of R,S-citronellol and R,S-linalool was shown for VvGT15a and VvGT14a, respectively. ABMP revealed geraniol as the major biological substrate but also disclosed that these UGTs may add to the production of further glycoconjugates in planta. ABMP of aglycone libraries provides a versatile tool to uncover novel biologically relevant substrates of small-molecule glycosyltransferases that often show broad sugar acceptor promiscuity.Plant secondary metabolites are frequently decorated with Glc that is transferred from uridine diphosphoglucose by a so-called family 1 URIDINE DIPHOSPHATE GLUCOSYLTRANSFERASE (UGT; Caputi et al., 2012). Since the glucosylation process can be envisaged as a simple nucleophilic displacement reaction of Secondorder Nucleophilic Substitution type, the product is a b-glucoside. A remarkably large array of different small molecules is glucosylated in planta, including terpenoids, alkaloids, cyanohydrins, and glucosinolates, as well as flavonoids, isoflavonoids, anthocyanidins, and phenylpropanoids. In grape (Vitis vinifera) alone, more than 200 different glucosides have been identified, and there is special interest in those glucoconjugates, which can contribute to wine flavor after the hydrolytic release of volatiles during the biotechnological vinification sequence leading from grape to aged wine (Wirth et al., 2001). These flavorless glucoconjugates accumulate in grape berries during maturation and can be grouped according to their linked aglycones into monoterpenes, C13-norisoprenoids, aliphatic alcohols, and shikimatederived benzoids and phenylpropanoids (Sefton et al., 1996). It still remains an open question how this large number of structurally different flavor precursors is actually glucosylated in vivo, because the in vitro activities of single UGTs show large differences in the individual range of acceptors. Some UGTs are considered highly specific with respect to substrate ...

Downy mildew, caused by the oomycete Plasmopara viticola, is one of the major threats to grapevine. All traditional cultivars of grapevine (Vitis vinifera) are susceptible to downy mildew, the control of which requires regular application of fungicides. In contrast, many sources of resistance to P. viticola have been described in the Vitis wild species, among which is V. amurensis Rupr. (Vitaceae), a species originating from East Asia. A genetic linkage map of V. amurensis, based on 122 simple sequence repeat and 6 resistance gene analogue markers, was established using S1 progeny. This map covers 975 cM on 19 linkage groups, which represent 82% of the physical coverage of the V. vinifera reference genetic map. To measure the general level of resistance, the sporulation of P. viticola and the necrosis produced in response to infection, five quantitative and semi-quantitative parameters were scored 6 days post-inoculation on the S1 progeny. A quantitative trait locus (QTL) analysis allowed us to identify on linkage group 14 a major QTL controlling the resistance to downy mildew found in V. amurensis, which explained up to 86.3% of the total phenotypic variance. This QTL was named 'Resistance to Plasmopara viticola 8' (Rpv8).

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Background and Aims: The influence of grapevine rootstocks on vine vigour and crop yield is recognized as an integral part of viticultural management. However, the genetic potential of Vitis species rootstock hybrids for vigour and yield control is not fully exploited in Australian viticulture. The effect of 55 novel inter-and intra-species hybrids and five traditional hybrid rootstock cultivars on winter pruning weight, berry size and fruit yield of grafted Shiraz vines is presented. The genetic predictions that resulted from this analysis were used to illustrate how rootstocks that best perform for a combination of traits may be selected. Methods and Results: The use of linear mixed models and residual maximum likelihood procedures took into account repeated measures and spatial variation within a large field trial (720 vines). Over 6 years of assessment, variation of up to 93.9% in winter pruning weight, 81.9% in fruit yield and 21.0% in berry weight between rootstocks was estimated. Conclusions: The effect of rootstock genotype accounted for marked differences in conferred pruning weight, berry weight and fruit yield from trial averages. Comparison of statistical analysis techniques illustrated that the choice of such techniques may influence the outcome of genetic selection from field trial data. Significance of the Study: Such quantification of the variation between vines in vigour, fruit yield and berry size due to rootstock genotype provides a framework for selection of well-performing genotypes for inclusion in advanced generations of the CSIRO vine rootstock breeding program.

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.

The influence of Ramsey, used as rootstock of the scion cvs Muscat Gordo Blanco (syn. Muscat of Alexandria), Shiraz (syn. Syrah), Riesling, Cabernet Sauvignon and Chardonnay, on the characteristics of the grape berries and of wine made from them was investigated, comparing ‘own‐rooted’ and ‘grafted’, and comparing wine fermented as juice (without skins) and must (juice and skins). The study involved the partitioning of K+ within berries, changes in juice K+, malic and tartaric acid through fermentation, wine inorganic ion and organic acid composition, and wine spectral characteristics. K+ concentration was higher in berries from grafted than from own‐rooted for all varieties except Chardonnay, and highest for grafted Shiraz. It was higher in skin than in pulp and seeds. In the pulp, it was highest for grafted Shiraz. K+ concentrations in all ferments using must (i.e. juice plus skins) increased during the initial two days after crushing, with the increase reflecting extraction from skins, being greatest for Shiraz and Muscat Gordo Blanco. Tartaric acid concentration in must also increased during the initial two days after crushing and then decreased. Malic acid concentration was higher in juice of Ramsey‐grafted than own‐rooted vines, especially for Shiraz; concentrations did not change markedly during the initial 12 days of fermentation, except where malo‐lactic fermentation occurred. Wine made from grapes of grafted contained significantly less tartaric and more malic acid than that made from own‐rooted for all varieties and for both fermentation types, with the exception of tartaric acid in wine of Muscat Gordo Blanco fermented as must. Wine made from juice had significantly higher tartaric acid and lower malic acid than that made from must for all varieties except for tartaric acid in wine from grafted Shiraz and malic acid in own‐rooted Chardonnay. Wine had a smaller tartaric acid/malic acid ratio when made from must. Wine pH was positively correlated with K+ but negatively with tartaric acid and with the tartaric acid to malic acid ratio. Overall, Shiraz wine contained highest Cl˜, Na+ and K+ concentrations. Red wines obtained from grafted had higher colour hue, especially those from Shiraz. Wines made from fruit borne on own‐rooted Cabernet Sauvignon had the highest concentration of total anthocyanins, ionised anthocyanins and total phenolics.

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