Denis Rusjan

Adjustments of water use efficiency by stomatal regulation during drought and recovery in the drought-adapted Vitis hybrid Richter-110 (V. berlandieri x V. rupestris).

The hybrid Richter-110 (Vitis berlandieri x Vitis rupestris) (R-110) has the reputation of being a genotype strongly adapted to drought. A study was performed with plants of R-110 subjected to water withholding followed by re-watering. The goal was to analyze how stomatal conductance (g(s)) is regulated with respect to different physiological variables under water stress and recovery, as well as how water stress affects adjustments of water use efficiency (WUE) at the leaf level. Water stress induced a substantial stomatal closure and an increase in WUE, which persisted many days after re-watering. The g(s) during water stress was mainly related to the content of ABA in the xylem and partly related to plant hydraulic conductivity but not to leaf water potential. By contrast, low g(s) during re-watering did not correlate with ABA contents and was only related to a sustained decreased hydraulic conductivity. In addition to a complex physiological regulation of stomatal closure, g(s) and rate of transpiration (E) were strongly affected by leaf-to-air vapor pressure deficit (VPD) in a way dependent of the treatment. Interestingly, E increased with increasing VPD in control plants, but decreased with increasing VPD in severely stressed plants. All together, the fine stomatal regulation in R-110 resulted in very high WUE at the leaf level. This genotype is revealed to be very interesting for further studies on the physiological mechanisms leading to regulation of stomatal responsiveness and WUE in response to drought.

The response of phenolic compounds in grapes of the variety ‘Chardonnay’ (Vitis vinifera L.) to the infection by phytoplasma Bois noir

The study was carried out on phytoplasma susceptible grapevine variety ‘Chardonnay’ (Vitis vinifera L.). The changes in total and individual phenolics, with a focus on hydroxycinnamic acids, flavanols and flavonol contents, were studied in phytoplasma-symptomatic and non-symptomatic berries of Bois noir (BN) infected and uninfected vines. Evident responses to BN infection at veraison have been monitored in a decreased accumulation of caftaric and coutaric acids, p-coumaroyl hexose, procyanidin B1, procyanidin trimer as well as of quercetin-3-O-glucoside, quercetin-3-O-glucuronide and quercetin-3-O-xyloside. At berry softening BN infection statistically increased the content of total phenolics, hydroxycinnamic acids and flavanols, but decreased the flavonol contents, especially at phytoplasma-symptomatic berry skins. Later, at harvest, the BN infection caused an additional significant decrease of coutaric acid and p-coumaroyl pentose contents, moreover of procyanidin B1 and procyanidin dimmers (1, 2, and 3), trimer, kaempferol-3-O-glucoside and of most identified quercetins, except of quercetin-3-O-xyloside. At harvest, non-symptomatic berries from infected plants showed similar dynamics in the total phenolic content compared to berry skins from uninfected plants, but in total flavanols and flavonols content similarity to those symptomatic was observed. The latter decreases grape quality and its antioxidant potential. The Bois noir disease showed specific, local and growth-phase-induced responses regarding the content of phenolics in berry skins, where in particular the differences between phytoplasma-symptomatic and non-symptomatic grapes have to be underlined.

Biochemical response of grapevine variety ‘Chardonnay’ (Vitis vinifera L.) to infection with grapevine yellows (Bois noir)

This study was carried out on the leaves of phytoplasma susceptible grapevine variety ‘Chardonnay’ (Vitis vinifera L.), and included research of the alterations in chlorophyll and carotenoid contents, contents of phenol compounds and in related enzymes activity in the phenylpropanoid pathway during the Bois noir (BN) infection. Phytoplasma-infected leaves showed reduced contents of chlorophylls and carotenoids, which promoted their susceptibility to oxidative reactions. Furthermore, modulation of flavonoid biosynthesis occurred in infected leaves, leading to an increased activity of phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase and polyphenoloxidase, but to a decreased peroxidase activity. Phytoplasma infection led to an increase of the contents of hydroxycinnamic acids (caftaric acid, sinapic acid glucose derivate and coutaric acid), flavanols (procyanidin B1, procyanidin dimer 3, catechin, epicatechin) and flavonols (quercetin 3-O-glucuronide, quercetin 3-O-glucoside) especially in the period up to vérasion. The study demonstrated that at certain phenological key-stages infection with phytoplasma (BN) induced different alterations in enzyme activities and in the contents of biochemical compounds from primary and secondary metabolism.

Genetic Characterization of Old Slovenian Grapevine Varieties of "Vitis vinifera" L. by Microsatellite Genotyping

Microsatellite genotyping of 38 local Slovenian varieties was performed using 11 SSR markers that have been shown to be highly polymorphic in European Vitis resources. Combining those data with previous studies, 49 unique genotypes were identified within the varieties currently cultivated in the Slovenian Primorje region. These genotypes were further compared to 161 cultivars from eight European countries to assess their genetic relationships. A high level of genetic diversity among Slovenian grapevines was revealed and some unknown relationships were discovered. Identity analyses revealed 11 groups of synonyms among Slovenian varieties and three matches between a Slovenian variety and a variety from other countries. Several groups of Slovenian varieties with similar names resulted in different SSR profiles. The genetic distances between varieties used in Slovenia and the most popular cultivars used in other European countries revealed the closest relationship with Croatian varieties and the most distant with French varieties.

Double maturation raisonnée: the impact of on-vine berry dehydration on the berry and wine composition of Merlot (Vitis vinifera L.)

BACKGROUND Double maturation raisonnée (DMR) is a potential canopy measure that affects grape and wine composition. The aim of this work was to study for the first time the DMR impact on the physical, biochemical and sensorial characteristics of the berries and wines of Merlot, one of the worlds fastest-expanding grapevine varieties. RESULTS DMR significantly increased the content of soluble solids (1.2-fold), free amino nitrogen (1.8-fold) and acidity in berries but decreased the weight of 100 berries on harvest (approx. 28%). Irrespective of the vintage, DMR-treated grapes had a significantly higher content of non-astringent tannins (0.73-0.78 mg L-1 ) and anthocyanin extractability (34.7-36.4%) but a lower index of astringency (31.2-33.7) when compared to the control. Consequently, the DMR wines achieved higher alcohol, total acidity and extract, hydroxycinnamic acids, flavanol and flavonol contents, whereas the content of anthocyanins was similar to that of the control. Sensorial evaluation showed that DMR wines were not rated higher and would not be appreciated more than control wines. CONCLUSION Changes in berries during DMR altered the wine characteristics only in terms of primary metabolites. A reduced accumulation of phenolics, especially anthocyanin content, in the berry skin of DMR-treated grapes was not reflected in their presence in wines. To the best of our knowledge, this is the first paper that has reported an impact of DMR on the grape and wine composition of Merlot, as one of the most promising red varieties.

The response of Monoterpenes to Different Enzyme Preparations in Gewürztraminer (Vitis vinifera L.) Wines

The α-terpineol, linalool, nerol and geraniol, which are the main aromatic monoterpenes in the grapevine variety Gewurztraminer, were determined in the grapes, must and wine after treatment with six different pectolytic enzymes [Lallzyme-β (‘Lall’); Rohavin VR-C (‘VRX’), Rohapect D5L (‘D5L’), Rohavin MX (‘MX’), Rohapect VRC (‘VRC’), Endozym cultivar A (‘Cult. A’)], and after treatment with β-glucosidase (βG, EC 3.2.1.21). The concentrations of monoterpenic compounds were determined by solid-phase microextraction (SPME) and GC-MS. The most abundant monoterpene in the grapes of Gewurztraminer was geraniol (66.7 μg/L), followed by nerol (13.3 μg/L), α-terpineol (7.8 μg/L) and finally linalool (3.3 μg/L). Gewurztraminer wine from must treated with the Lall enzyme preparation was the most aromatic, which was also confirmed by chemical and sensory analysis in which the concentrations of nerol (45.9 μg/L), geraniol (31.8 μg/L), α-terpineol (10.5 μg/L) and linalool (6.1 μg/L) were determined. The wines produced from must treated chemically with enzymes showed higher concentrations of many of the monoterpene compounds compared to the control, although the sensorial analysis did not affirm this convincingly.

Aromas in Grape and Wine

Aromatic compounds are an important quality parameter of grape and wine, which has gained further importance with consumer demand. The extraction methods and analytical techniques used should be quick, inexpensive, with high reproducibility and sensibility, and require a low volume of sample and automated for the major part. A procedure of solid-phase microextraction (DVB/CAR/PDMS fibre) for few aroma compounds from grape, musts and wines has been developed and the analyses were performed by Gas chromatography-Mass spectrometry (GC-MS). Different hydrolytic approaches were also tested; the most successful were enzymatic hydrolysis (with two different enzymes) and acidic hydrolysis at pH 3.00. Non-hydrolysed terpene glycosides were extracted from the musts using solid-phase extraction . The extract was analysed with Liquid chromatography-Mass spectrometry (LC-MS) and some compounds were tentatively identified as terpene glycosides . The selection of the methods and techniques of aroma determination in grape or wine should be made according to laboratory capacity, equipment, time, number of samples, budget and the group of aroma compounds to evaluate.

Biochemical composition of different table grape cultivars produced in Slovenia

ABSTRACT In a three-vintage (2014–2016) experiment, the fruit quality of 20 table grape cultivars was observed. The morphometric and chemical characteristics of the berries were evaluated at the edible grape stage, using OIV descriptors, colorimeter (CIRG index) and HPLC for measurements of sugars, organic acids and vitamin C contents. The cultivars ‘Michele Palieri’ and ‘Italia’ had significantly the highest berry weight (8.2 to 9.7 g), while ‘Perlette’, ‘Esther’, ‘Nero’, ‘Panse precoce’ and ‘Chasselas rouge’ had a lower (2.1 to 2.7 g) weight. Significantly, the lowest CIRG index was found with the cultivars ‘Victoria’, ‘Italia’ and ‘Perlette’ (0.99 to 1.3), and the highest with ‘Perlon’ and ‘Muscat de Hambourg’ (4.8 and 5.2, respectively). Berries of ‘Muscat bleu’ (147.3 g/kg FW) and ‘Nero’ (133.3 g/kg FW) had significantly the highest sugar content, while ‘Michele Palieri’, ‘Victoria’, ‘Italia’, ‘Matilde’ and ‘Queen of vineyards’ (75.9 to 92.08 g/kg FW) had the lowest. The highest organic acid contents were achieved by ‘Ribol’, ‘Perlette’, ‘Italia’, ‘Muscat bleu’ and ‘Lival’ (9.6 to 10.8 g/kg FW), while ‘Queen of vineyard’, ‘Ora’, ‘Perlon’ and ‘Victoria’ (5.8 to 7.1 g/kg FW) were the lowest. In terms of the sugars/acids ratio, ‘Ora’ had the highest (19.1), resulting in the sweetest taste, while ‘Italia’, with a ratio of 8.9, had a sour taste. However, ‘Panse precoce’, ‘Matilde’ and ‘Queen of vineyards’ had significantly the highest content of vitamin C (7.3 to 9.5 g/kg FW), while ‘Muscat bleu’, ‘Nero’, ‘Panse precoce’ and ‘Ribol’ had the highest total phenolics (1.27 to 1.57 g GAE/kg FW). The results suggest that the studied interspecific grapevine cultivars (‘Muscat bleu’, ‘Esther’, ‘Nero’ and ‘Presentabil’) showed an interesting chemical composition, while morphometrically they still fall behind Vinifera varieties.