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Xylem vessels are essential pivotal organs in bulk hydraulic flow through the whole woody plant. However, environmental constraints generate disagreements in xylem structures, which are characterized by air emboli and occlusions formations, compromising water conductivity in grapevines. The aim of this work was to explore xylem morphology dynamics through the xylem sap flow of five Tunisian grapevine cultivars during the natural bleeding sap periods of 2019, 2021, and 2022. In fact, Sakasly, Khamri, Hencha, Razegui1, and Razegui2 rain-fed grapevine cultivars revealed differential responses towards xylem sap movement. The results demonstrated that the xylem sap flow was significantly more abundant in 2019 than 2021 and 2022 bleeding sap campaigns. A variation was revealed between the cultivars regarding the xylem sap flow. In fact, Sakasly gave the best xylem flow during the three campaigns. Razegui1 and Razegui2 registered approximately similar xylem sap flow, while Hencha and Khamri present the lowest sap fluxes during the three campaigns. Moreover, several vascular occlusions forms were identified from stem cross sections using environmental scanning electron microscopy (ESEM), including tyloses, gels, starch, and gum deposits. The highest occlusion number was observed in Sakasly, Razegui1, and Razegui2 cultivars. Among different biogenic calcium shapes, several were observed for the first time in grapevine, including multi-faceted druse, cubic, crystalline sand, styloids, spherical, or drop-like structures. Considering their lower flow and totally blocked vessels, both Hencha and Khamri confirmed their susceptibility to environmental constraints. However, Sakasly, Razegui1, and Razegui2 cultivars presented higher tolerance according to their sap flow and xylem morphology. [ABSTRACT FROM AUTHOR]

To identify and isolate genes related to abiotic stress (salinity and drought) tolerance in grapevine, a candidate gene approach led to the isolation from Cabernet Sauvignon cultivar of a full-length cDNA of dehydrin gene. he latter, named VvDhn, which is highly and mainly induced in late embryogenesis in seeds, encodes for a protein of 124 amino acids with a predicted molecular mass of 13.3 kDa. Details of the physicochemical parameters and structural properties (molecular mass, secondary structure, conserved domains and motives, and putative posttranslational modification sites) of the encoded protein have also been elucidated. he expression study of VvDhn was carried out within plant organs and tissues as well as under drought and salt stresses. VvDhn was not detected in vegetative tissue, whereas it was only expressed during seed development (during late embryogenesis) at extremely high levels and was induced by salt and drought stresses as well as ABA application. Moreover, salt stress induced VvDhn expression in the tolerant variety (Razegui) but not the sensitive variety (Syrah), which did not display expression variation during stress; VvDhn expression level and salt-stress response depend on regulatory mechanisms that are efficient only in the tolerant variety. On the other hand, under drought stress VvDhn was induced in both tolerant and sensitive varieties, with higher levels in the tolerant variety. In addition, stress signal molecules such as ABA (applied alone or in combination with saccharose) induced VvDhn expression, even at low levels. Minimal knowledge about the role and functionality of this gene is necessary and constitutes a prerequisite for including VvDhn in grapevine abiotic stress tolerance improvement programs. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assessed population structure in Tunisian Vitis sylvestris using SSRs. [•] Genetic and demographic data highlighted high extinction level within this flora. [•] Various conservation plans were suggested for best management of grapevine. [Copyright &y& Elsevier]

An efficient protein extraction method is crucial to ensure successful separation by two-dimensional electrophoresis (2-DE) for recalcitrant plant species, in particular for grapevine ( Vitis vinifera L.). Trichloroacetic acid-acetone (TCA-acetone) and phenol extraction methods were evaluated for proteome analysis of leaves and roots from the Tunisian cultivar 'Razegui'. The phenol-based protocol proved to give a higher protein yield, a greater spot resolution, and a minimal streaking on 2-DE gels for both leaf and root tissues compared with the TCA-based protocol. Furthermore, the highest numbers of detected proteins on 2-DE gels were observed using the phenol extraction from leaves and roots as compared with TCA-acetone extraction. [ABSTRACT FROM AUTHOR]

Proteomic and transcriptomic analyses of pathogenesis-related proteins, PR10, were carried out by subjecting adult plants of the salt-tolerant grapevine cv. Razegui to 100 mM NaCl for 6 and 24 h under controlled greenhouse conditions. Within 6 h of salt exposure, an increase in levels of RzPR10 was observed in the roots. PR10 mRNA levels in leaves were significantly different than those in roots; moreover, significant differences for mRNA levels were found between treated and control plants. Within 24 h of salt treatment, roots exhibited the highest levels of RzPR10 protein, but no differences were observed for mRNA levels in both leaves and roots. Overexpression of Vvpr10 cDNA, under the control of the Gal promoter, in the yeast Saccharomyces cerevisiae revealed that growth of transformed cells on a minimal medium containing 500 mM NaCl is similar to that of cells cultivated on NaCl-free medium. This indicated that Vvpr10 gene was functional in yeast and conferred tolerance to high salt concentrations. [ABSTRACT FROM AUTHOR]

This study investigated the effects of temperature (15 to 37 °C) and water activity (0.90 to 0.99) on the growth and production of ochratoxin A (OTA) by Aspergillus carbonarius cultured on synthetic nutrient medium (SNM) after 5 and 10 d of incubation. Total of 8 ochratoxigenic A. carbonarius, isolated from vineyards located in different regions of Tunisia, were used. Growth data were modeled by the flexible model of Baranyi and growth rates at each set of conditions were obtained. For both growth and OTA production, optimal water activity was 0.99; however, optimal temperature varied. The optimal temperature for growth was 30 °C. At 37 °C, the growth rate decreased significantly ( P < 0.05). Maximum toxin production occurred at temperatures in the range of 15 to 25 °C with the optimum one depending on the isolate tested. Significant amounts of OTA were produced after only 5 d of incubation. Our results showed that A. carbonarius isolated from Tunisian grapes behave as those from European and Australian grapes, as reported in the literature, although some differences in trends for growth and OTA production were observed. [ABSTRACT FROM AUTHOR]

The aroma composition of the grape juice of Khamri, a native variety of Vitis vinifera grown in Tunisia, was investigated for the first time. A total of 27 free and 20 glycosidically bound compounds were identified by gas chromatography-mass spectrometry. According to the obtained results, the aroma compounds were C6 alcohols, benzene compounds, terpenes, acids and norisoprenoids. On the basis of gas chromatography-olfactometry, these compounds were grouped, according to volatiles exhibiting the identical odor quality, into 10 groups of the same character (aromatic series) as a way of establishing an aroma profile for the studied variety. The high glycosidically bound norisoprenoid concentrations and the absence of the bound form of the acids were a positive factor for the Khamri variety potential aroma. PRACTICAL APPLICATIONS This article aimed on the identification of the unknown Tunisian grapevine varieties that are very well adapted to the arid conditions and that could have a good quality. The discovery of unknown autochthonous grapevine varieties with good aroma and pomological characteristics could be of great importance for the agriculture sector all over the world especially the arid regions. [ABSTRACT FROM AUTHOR]

Abstract: This paper summarizes the results of a large study on the occurrence of ochratoxigenic fungi and Ochratoxin A from wine and table grapes in Tunisia. Our results revealed that Aspergillus section Nigri were the unique potential OTA producing fungi isolated from grapes. Isolates belonging to Aspergillus niger aggregate were the most abundant species followed by Aspergillus carbonarius isolates, then uniseriate aspergilli. A. carbonarius presented the highest percentage of OTA-positive strains (97%) whereas only 3% of A. niger aggregate isolates were OTA positive. Grapes were analysed for their OTA content and 58% of them contained detectable levels of OTA, between 0.05 and 5.85 μg/l. Only 4 samples out of 39 exceeded the OTA limit of 2 μg/l fixed by the EU for wine and grape juices. The most contaminated grapes were those from Raf–Raf region located in the North-Est and characterized by a humid climate. Grapes from the Regueb region, characterized by an arid climate, were rarely contaminated. Furthermore, A. carbonarius, which is the main OTA producer fungi on grapes, was rarely isolated in Regueb. [Copyright &y& Elsevier]

Abstract: Salt stress adversely affects the growth of grapevine plants. In order to understand the molecular basis of salt stress response in grapevine plants, suppression subtractive hybridization (SSH) and microarray based screening approaches were combined. Two leaf-specific subtractive cDNA libraries were constructed from grapevine plants subjected to a moderate, incremental salt stress treatment. SSH were performed 6h and 24h after NaCl peaked at 100mM using cDNAs prepared from leaves of a salt tolerant cultivar (Razegui) as testers and cDNAs from unstressed leaves as drivers. Then, a pre-screened subset of cDNA clones from these SSH libraries were used to construct a Vitis vinifera cDNA array, in order to verify the expression changes of the genes upon salt treatment. Expression profiles were compared between the salt tolerant and a susceptible cultivar (Syrah) under both control conditions and after salt stress treatment. Seven cDNA clones were identified which were up-regulated by salt stress in two independent growth experiments and confirmed by RNA blot analysis. The transcript expression patterns of the selected genes differed between the contrasting grapevine cultivars tested with respect to stress-regulation. The possible relationship of individual cDNAs with salinity tolerance mechanisms is discussed. [Copyright &y& Elsevier]

The preservation of embryogenic lines derived from several endangered local grapevine cultivars was studied. Embryogenic calluses were obtained from immature anthers of eight cultivars, sampled on both fruity-cuttings and field grown vines. Anthers at the 'separated flower' stage, derived from fruity-cuttings, resulted in an increased induction of somatic embryogenesis, compared to those derived from the field. Pro-embryogenic calluses were induced on Chùe and Pool (1987) basal medium, supplemented with 9 μM of 2,4-dichlorophenoxyacetic acid (2,4-D) and 11.35 μM of thidiazuron (TDZ) under dark conditions. Different anther zones (filament, abaxial, adaxial, lateral zones and entire anthers) were involved in somatic embryogenesis induction. The percentages of granular and yellowish pro-embryogenic call uses ranged between 15.6% and 34.8% in 'Kahli Kerkennah' and 'Muscat Raf-raf' cultivars, respectively. Although, morphological diversifications of pro-embryogenic calluses (several necrosis and spontaneous maturation) were observed on the induction medium after 5 subcultures. The reduction of 2,4-D and TDZ levels to 4.52 μM and 2.89 μM respectively, induced granular and yellowish embryogenic material. Thus, Chée and Pool (1987) (CP) enriched with 4.52 μM of 2,4-D and 2.89 μM of TDZ revealed to be the most appropriate for long-term maintenance. In fact, all the cultivars presented high and regular embryo maturation rates after 12, 24, 36 and 48 months of cultivation on this medium, under light conditions. After 4 years, they still exhibit high germination and regeneration abilities. Germination of somatic embryos was achieved on Murashige and Skoog (1962) basal-medium, with rates ranging from 69% to 96%. Only 5% of somatic embryos were concerned by morphological variations. The regenerated plantlets presented a normal phenotype under controlled greenhouse conditions, compared to mother plants. [ABSTRACT FROM AUTHOR]

Abstract: The occurrence of ochratoxin A (OTA) and the identification of the ochratoxigenic microbiota in Tunisian grapes were studied for the first time. Black aspergilli were the dominant genus among the filamentous fungi isolated from grapes and were the only potential OTA-producing fungi found. The most abundant species were member of Aspergillus niger aggregate (63%) and Aspergillus carbonarius (36%). Uniseriate aspergilli were rarely present (1%). Of the A. carbonarius isolates, 97% were OTA positive but only 3% of the A. niger aggregate isolates were OTA positive. During grape maturation, the frequency of black aspergilli increased due to increase of the numbers of A. carbonarius. Musts (n =24) obtained from grapes collected at the different sampling times were analyzed for their OTA content. Up to 37% of the musts contained OTA at levels varying between 0.59 and 2.57 μg/l. The amounts of OTA in musts increased as grapes matured. These results indicate that A. carbonarius is the main cause of OTA contamination of Tunisian grapes. [Copyright &y& Elsevier]