Luca Mercenaro

NMR Analysis of Seven Selections of Vermentino Grape Berry: Metabolites Composition and Development

The goal of this work was to study via NMR the unaltered metabolic profile of Sardinian Vermentino grape berry. Seven selections of Vermentino were harvested from the same vineyard. Berries were stored and extracted following an unbiased extraction protocol. Extracts were analyzed to investigate variability in metabolites concentration as a function of the clone, the position of berries in the bunch or growing area within the vineyard. Quantitative NMR and statistical analysis (PCA, correlation analysis, Anova) of the experimental data point out that, among the investigated sources of variation, the position of the berries within the bunch mainly influences the metabolic profile of berries, while the metabolic profile does not seem to be significantly influenced by growing area and clone. Significant variability of the amino acids such as arginine, proline, and organic acids (malic and citric) characterizes the rapid rearrangements of the metabolic profile in response to environmental stimuli. Finally, an application is described on the analysis of metabolite variation throughout the physiological development of berries.

Distinctive Anthocyanin Accumulation Responses to Temperature and Natural UV Radiation of Two Field-Grown Vitis vinifera L. Cultivars

The responses of two red grape varieties, Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache), to temperature and natural UV radiation were studied in a three-years field experiment conducted in Sardinia (Italy), under Mediterranean climate conditions. Vines were covered with plastic films with different transmittances to UV radiation and compared to uncovered controls. Light intensity and spectral composition at the fruit zone were monitored and berry skin temperature was recorded from veraison. Total skin anthocyanin content (TSA) and composition indicated positive but inconsistent effects of natural UV light. Elevated temperatures induced alterations to a greater extent, decreasing TSA and increasing the degree of derivatives acylation. In Cannonau total soluble solids increases were not followed by increasing TSA as in Bovale Grande, due to both lower phenolic potential and higher sensitivity to permanence of high temperatures. Multi linear regression analysis tested the effects of different ranges of temperature as source of variation on anthocyanin accumulation patterns. To estimate the thermal time for anthocyanin accumulation, the use of normal heat hours model had benefit from the addition of predictor variables that take into account the permanence of high (>35 °C) and low (<15 °C and <17 °C) temperatures during ripening.

Responses of Fruit Uniformity to Deficit Irrigation and Cluster Thinning in Commercial Winegrape Production

Fruit uniformity is generally regarded as an essential quality parameter in winegrape production. Deficit irrigation and cluster thinning are popular techniques to improve fruit quality, but there is little empirical information on how these practices influence fruit uniformity in the field. Deficit irrigation and targeted cluster thinning treatments were imposed in a commercial Cabernet Sauvignon vineyard in Dunnigan Hills, California, for three consecutive years. Fruit uniformity measures at three levels (blocks, vines, and clusters) were evaluated using variance components analysis and ANOVA on absolute residuals (Levene’s test). Regardless of the irrigation treatment, cluster-to-cluster variation within vines was the primary source of fruit variability each season. In general, postveraison irrigation deficits decreased cluster-to-cluster uniformity for Brix and fruit anthocyanin content. While the decrease in anthocyanin content uniformity was due to unevenness of fruit anthocyanin synthesis/loss, the decrease in Brix uniformity was due to unevenness in fruit shriveling. Cluster thinning increased Brix uniformity at veraison, but there was no effect at harvest on fruit composition and berry size uniformity. Brix uniformity was not correlated to crop load, pruning weight, or the pruning weight/crop load ratio, but an increase in Brix uniformity did occur as fruit matured.

Sequence Polymorphisms and Structural Variations among Four Grapevine (Vitis vinifera L.) Cultivars Representing Sardinian Agriculture

The genetic diversity among grapevine (Vitis vinifera L.) cultivars that underlies differences in agronomic performance and wine quality reflects the accumulation of single nucleotide polymorphisms (SNPs) and small indels as well as larger genomic variations. A combination of high throughput sequencing and mapping against the grapevine reference genome allows the creation of comprehensive sequence variation maps. We used next generation sequencing and bioinformatics to generate an inventory of SNPs and small indels in four widely cultivated Sardinian grape cultivars (Bovale sardo, Cannonau, Carignano and Vermentino). More than 3,200,000 SNPs were identified with high statistical confidence. Some of the SNPs caused the appearance of premature stop codons and thus identified putative pseudogenes. The analysis of SNP distribution along chromosomes led to the identification of large genomic regions with uninterrupted series of homozygous SNPs. We used a digital comparative genomic hybridization approach to identify 6526 genomic regions with significant differences in copy number among the four cultivars compared to the reference sequence, including 81 regions shared between all four cultivars and 4953 specific to single cultivars (representing 1.2 and 75.9% of total copy number variation, respectively). Reads mapping at a distance that was not compatible with the insert size were used to identify a dataset of putative large deletions with cultivar Cannonau revealing the highest number. The analysis of genes mapping to these regions provided a list of candidates that may explain some of the phenotypic differences among the Bovale sardo, Cannonau, Carignano and Vermentino cultivars.

Intra-varietal Agronomical Variability in Vitis vinifera L. cv. cannonau investigated by fluorescence, texture and colorimetric analysis

To date, innovative, rapid and non-invasive techniques have been used to assess variations in morphological and technological characteristics between grape cultivars. In order to improve knowledge of the qualitative expression of the genetic traits of cv. Cannonau (syn. Grenache), fluorescence, texture and colorimetric analyses were performed on 85 biotypes attributable to this variety. Eighty-five Cannonau biotypes cultivated in the same vineyard were analysed in order to evaluate their morphological and agronomical characteristics. As regards the morphological traits, of the six descriptors observed, five were able to discriminate the Cannonau population according to different expression levels. Must composition, berry colour (using the Minolta tristimulus colorimeter), texture (assessed using the TaxT2i plus texturimeter) and fluorescence (using the Multiplex III detector) were determined on clusters harvested at the same time. Cluster analysis was able to separate the Cannonau population into five groups, characterised by differences in the following criteria: L*, a* and b*, berry skin thickness, FERARI, TSS, pH and titratable acidity, total polyphenols and total anthocyanins. The FERARI index was highly and positively correlated with total anthocyanins and negatively correlated with grape colour, while berry weight and berry skin thickness were not correlated with any variable assessed. The remarkable intra-variability encountered for the qualitative and quantitative characters in the Cannonau variety suggests that new biotypes could be selected for different oenological purposes, using techniques such as the measure of fluorescence and colorimetry. This is the first study carried out within the cv. Cannonau using innovative and classical techniques suitable to investigate intra-varietal variability.

Primary and secondary characterization of a Vermentino grape clones collection

Vermentino is one of the main grape variety cultivated in the west Mediterranean region, mainly in France (Provence and Corsica) and in Italy (Sardinia, Tuscany and Ligury). Due to the high quality of its monovarietal wines, Vermentino has increased its importance in the last two decades, while previously has been regarded as a minor variety covering small surfaces. Through clonal selection Vermentino clones have been patented and diffused among growers in Corsica and in Italy. On a collection of 14 Italian and Corsican Vermentino clones, ex situ preserved in Sardinia, ampelographic data, phenological stages, and agronomic characteristics, such as yield, bud fertility, bunch and berry weight, pH, acidity and SST of must, were recorded from 2004 to 2005. The description of the Vermentino genotypes evidenced the identities and the distinctive traits within the clones collection, increasing the information on their agronomic performance in a common area of cultivation.