D. Grossi

Stem Xylem Characterization for Vitis Drought Tolerance

Together with stomatal conductance and root conductivity, the stem water reserve and transport systems could be regulatory mechanisms able to participate in the regulation of the plant water status. Lianas, such as Vitis spp., minimize the trunk support role, and stems have evolved to improve their ability in water transport. In this work, stems of 10 different Vitis species were studied in relation to their expected drought tolerance using reflectance spectroscopy. Spectra were measured before (T0) and after coloration with Sudan IV dye. The T0 spectral signature showed characteristic species features. The partial least squares (PLS) regression and the self-organizing map (SOM) neural network analysis were able to predict the expected drought tolerance score; thus, reflectance spectroscopy was demonstrated to be a useful technique for drought tolerance phenotyping. These methods could be applied for the preliminary selection of new rootstocks/cultivars. Wood composition variation appeared to be correlated with the water stress susceptibility. To clarify this relationship, the attention was focused on the wood hydrophobicity. Sudan IV is a microscopy dye traditionally used to underline suberin, waxes, and, in general, hydrophobic substances. Differences between rough and colored spectra evidenced the absorption band of Sudan IV with a maximum at 539 nm. The coloration intensity was used to develop a hydrophobicity index. The obtained values were correlated with the expected drought tolerance score. Therefore, hydrophobic compounds seem to play an important role in water use efficiency, and an hydrophobic barrier in the xylem tissue appears to be a protective mechanism against water stress.

Water deficit effects on grapevine woody tissue pigmentations

Grossi D., Rustioni L., Simone Di Lorenzo G., Failla O., Brancadoro L. (2016): Water deficit effects on grapevine woody tissue pigmentations. Hort. Sci. (Prague): 43: 188–194. Water availability is an important environmental factor in viticulture. In a climate change context, vineyard management should be adapted to the new conditions. Drought-resistant rootstocks need to be selected. In this paper, reflectance spectroscopy is proposed as a new method to characterize the water stress effects on woody section pigmentations. Cabernet Sauvignon grafted on 4 different rootstocks (140Ru, 420A, M2 and M3) represented the plant material. Greenhouse controlled conditions allowed the comparison of well-watered (WW) and water-stressed (WS) plants. The physiological responses were characterized concerning daily water consumption, stem water potential, gas exchange, and plant growth. The water use efficiency was calculated and discussed as well. Spectroscopy analyses of woody sections indicated a major absorption band probably related to phenolic derivatives. Water stress produced characteristic spectrum modifications both in the Cabernet Sauvignon stem and in the rootstock xylem. These preliminary results encourage further studies addressed at the evaluation of drought-resistant genotypes, to distinguish their stress responses and to characterize the compositional aspects linked to drought tolerance.

Grapevine field experiments reveal the contribution of genotype, the influence of environment and the effect of their interaction (GxE) on berry transcriptome

Changes in the performance of genotypes in different environments are defined as genotype × environment (G×E) interactions. In grapevine (Vitis vinifera), complex interactions between different genotypes and climate, soil and farming practices yield unique berry qualities. However, the molecular basis of this phenomenon remains unclear. To dissect the basis of grapevine G×E interactions we characterized berry transcriptome plasticity, the genome methylation landscape and within-genotype allelic diversity in two genotypes cultivated in three different environments over two vintages. We identified, through a novel data-mining pipeline, genes with expression profiles that were: unaffected by genotype or environment, genotype-dependent but unaffected by the environment, environmentally-dependent regardless of genotype, and G×E-related. The G×E-related genes showed different degrees of within-cultivar allelic diversity in the two genotypes and were enriched for stress responses, signal transduction and secondary metabolism categories. Our study unraveled the mutual relationships between genotypic and environmental variables during G×E interaction in a woody perennial species, providing a reference model to explore how cultivated fruit crops respond to diverse environments. Also, the pivotal role of vineyard location in determining the performance of different varieties, by enhancing berry quality traits, was unraveled.

Characterization of iron deficiency symptoms in grapevine (Vitis spp.) leaves by reflectance spectroscopy

The work aims at the description of the iron deficiency symptoms in grapevine leaves by reflectance spectroscopy at the plant and leaf levels. 5 genotypes of Vitis spp. were selected and grown in hydroponic conditions with and without iron supply. 450 spectra were collected among basal, young and apical leaves, as well as veins and interveinal areas. Iron deficiency produced significant and characteristic modifications in the pigment accumulation, proportion and distribution in plants. Basal leaves resulted to have higher concentrations of photosynthetic pigments in stressed plants with respect to the control, probably due to compensation effects. Iron deficient plants had lower chlorophyll concentrations in young and apical leaves. In the apical zone, also the relative composition of pigments appeared to be modified, explaining the reddish-yellowish apex appearance of iron deficient vines. Finally, the pigment distribution along the shoot characterized the symptoms, as well as the spectral variations among veins and interveinal areas. These results could support future applications in vineyard management (e.g.: symptom identification and detection; precision fertilization) as well as breeding programs for new rootstock selections (e.g.: fast screenings of seedlings).

Multi-parameter characterization of water stress tolerance in Vitis hybrids for new rootstock selection

Drought in grapevine could be faced using tolerant rootstocks. The present work aims at the evaluation of 25 new genotypes potentially tolerant to drought by using recent methods of phenotypical screening (thermography and on-solid reaction spectroscopy). Plants were grown in well-watered and stressed field conditions. Proxi for transpiration, wood hydrophobicity and starch content were used to characterize and classify the genotypes. The predominant role of the environment was highlighted, nevertheless genotype and genotype × environment interaction showed significant variations as well. Hybrids were classified based on their steady, susceptible or adaptable behavior. The 14 most promising genotypes were identified, 5 of them showing two tolerance mechanisms. In the future, results from this experiment will support viticulture in water limited areas releasing new drought-tolerant interspecific hybrids to be tested after grafting with different scions.