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Concept: Phylloxera

169

Vitis vinifera scions are commonly grafted onto rootstocks of other grape species to influence scion vigour and provide resistance to soil-borne pests and abiotic stress; however, the mechanisms by which rootstocks affect scion physiology remain unknown. This study characterized the hydraulic physiology of Vitis rootstocks that vary in vigour classification by investigating aquaporin (VvPIP) gene expression, fine-root hydraulic conductivity (Lp®), % aquaporin contribution to Lp®, scion transpiration, and the size of root systems. Expression of several VvPIP genes was consistently greater in higher-vigour rootstocks under favourable growing conditions in a variety of media and in root tips compared to mature fine roots. Similar to VvPIP expression patterns, fine-root Lp® and % aquaporin contribution to Lp® determined under both osmotic (Lp®(Osm)) and hydrostatic (Lp®(Hyd)) pressure gradients were consistently greater in high-vigour rootstocks. Interestingly, the % aquaporin contribution was nearly identical for Lp®(Osm) and Lp®(Hyd) even though a hydrostatic gradient would induce a predominant flow across the apoplastic pathway. In common scion greenhouse experiments, leaf area-specific transpiration (E) and total leaf area increased with rootstock vigour and were positively correlated with fine-root Lp®. These results suggest that increased canopy water demands for scion grafted onto high-vigour rootstocks are matched by adjustments in root-system hydraulic conductivity through the combination of fine-root Lp® and increased root surface area.

Concepts: Gene, Grafting, Root, Plant reproduction, Grape, Viticulture, Phylloxera, Rootstock

28

Grapevine leafroll disease (GLRD) is one of the most economically important virus diseases of grapevine (Vitis spp.) worldwide. In this study, we used high-throughput sequencing of cDNA libraries made from small RNAs (sRNAs) to compare profiles of sRNA populations recovered from own-rooted Merlot grapevines with and without GLRD symptoms. The data revealed the presence of sRNAs specific to Grapevine leafroll-associated virus 3, Hop stunt viroid (HpSVd), Grapevine yellow speckle viroid 1 (GYSVd-1) and Grapevine yellow speckle viroid 2 (GYSVd-2) in symptomatic grapevines and sRNAs specific only to HpSVd, GYSVd-1 and GYSVd-2 in nonsymptomatic grapevines. In addition to 135 previously identified conserved microRNAs in grapevine (Vvi-miRs), we identified 10 novel and several candidate Vvi-miRs in both symptomatic and nonsymptomatic grapevine leaves based on the cloning of miRNA star sequences. Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) of selected conserved Vvi-miRs indicated that individual members of an miRNA family are differentially expressed in symptomatic and nonsymptomatic leaves. The high-resolution mapping of sRNAs specific to an ampelovirus and three viroids in mixed infections, the identification of novel Vvi-miRs and the modulation of certain conserved Vvi-miRs offers resources for the further elucidation of compatible host-pathogen interactions and for the provision of ecologically relevant information to better understand host-pathogen-environment interactions in a perennial fruit crop.

Concepts: DNA, RNA, Vitis vinifera, Grape, Vitis, Vitaceae, Viticulture, Phylloxera

4

The plant compartments of Vitis vinifera, including the rhizosphere, rhizoplane, root endosphere, phyllosphere and carposphere, provide unique niches that drive specific bacterial microbiome associations. The majority of phyllosphere endophytes originate from the soil and migrate up to the aerial compartments through the root endosphere. Thus, the soil and root endosphere partially define the aerial endosphere in the leaves and berries, contributing to the terroir of the fruit. However, V. vinifera cultivars are invariably grafted onto the rootstocks of other Vitis species and hybrids. It has been hypothesized that the plant species determines the microbiome of the root endosphere and, as a consequence, the aerial endosphere. In this work, we test the first part of this hypothesis. We investigate whether different rootstocks influence the bacteria selected from the surrounding soil, affecting the bacterial diversity and potential functionality of the rhizosphere and root endosphere.

Concepts: Plant, Root, Vitis vinifera, Grape, Vitis, Vitaceae, Viticulture, Phylloxera

3

Downy mildew resistance across days post-inoculation, experiments, and years in two interspecific grapevine F1 families was investigated using linear mixed models and Bayesian networks, and five new QTL were identified. Breeding grapevines for downy mildew disease resistance has traditionally relied on qualitative gene resistance, which can be overcome by pathogen evolution. Analyzing two interspecific F1 families, both having ancestry derived from Vitis vinifera and wild North American Vitis species, across 2 years and multiple experiments, we found multiple loci associated with downy mildew sporulation and hypersensitive response in both families using a single phenotype model. The loci explained between 7 and 17% of the variance for either phenotype, suggesting a complex genetic architecture for these traits in the two families studied. For two loci, we used RNA-Seq to detect differentially transcribed genes and found that the candidate genes at these loci were likely not NBS-LRR genes. Additionally, using a multiple phenotype Bayesian network analysis, we found effects between the leaf trichome density, hypersensitive response, and sporulation phenotypes. Moderate-high heritabilities were found for all three phenotypes, suggesting that selection for downy mildew resistance is an achievable goal by breeding for either physical- or non-physical-based resistance mechanisms, with the combination of the two possibly providing durable resistance.

Concepts: Gene, Genetics, Evolution, Vitis vinifera, Grape, Vitis, Vitaceae, Phylloxera

3

The technological advances of RNA-seq and de novo transcriptome assembly have enabled genome annotation and transcriptome profiling in highly heterozygous species such as grapevine (Vitis vinifera L.). This work is an attempt to utilize a de novo-assembled transcriptome of the V. vinifera cultivar ‘Riesling’ to improve annotation of the grapevine reference genome sequence.

Concepts: Gene, RNA, Vitis vinifera, Grape, Vitis, Vitaceae, Viticulture, Phylloxera

3

Although domestication of the grapevine (Vitis vinifera L.) has been extensively documented, the history of genotype selection and evolution of vineyard management remain relatively neglected fields of study. The find of 454 waterlogged grapevine pips from a well-dated Etrusco-Roman site in the Chianti district (Tuscany, Central Italy) is an extraordinary chance to gain insights into the progress of viticulture occurring in a key historical period in one of the world’s most famous wine regions. The molecular and geometrical analyses of grape seeds showed (a) the presence in the site of different grapevine individuals and (b) a sudden increase in pip size, occurring at around 200 BC, whic explainable by the selection and introduction of new varieties. In this period, the Etruscans settlers in Chianti were stimulated by northward-expanding Roman culture to use novel vineyard management practices. We hypothesize that one of the most important innovations may have been the introduction of pruning, inducing vine physiological conditions more favorable to pip growth. Such changes were the consequence of specific entrepreneurial choices made by the Romans in a period of economic investment in grape cultivation and wine making to satisfy the increased trade demand after the conquest of the Central-Western Mediterranean basin.

Concepts: Vitis vinifera, Wine, Grape, Vitis, Vitaceae, Viticulture, Ancient Rome, Phylloxera

3

The importance and extent of wine consumption in all life aspects at the Holy Land is well documented. The Muslim influence in this region led to the abandonment of winemaking practices, and possible loss of indigenous wine varieties. Here we present a country wide collection of the local grapevine population including wild and cultivated forms, and its characterization by genetic, ampelographic and enological methods. The ampelographic analysis shows clear differences between Sativa and Sylvestris groups in flower, leaf and cluster parameters, and that most Sativa belong to proles orientalis. Genetic population analysis was conducted by analyzing 22 common SSR markers, determining first the unique genotypes, and internally assessing the population’s structure, showing the existence of two distinct Sativa and Sylvestris populations, and a third mixed one. Likewise, the relationship between the Israeli grapevine population and grapevine populations in Europe and parts of Asia was investigated, showing that the Israeli Sativa and Sylvestris populations cluster closely together, suggesting a common genetic source. Lastly, the enological characteristics of selected Sativa and Sylvestris genotypes are presented, demonstrating their potential for quality wine production. This research significantly contributes toward the re-establishment of indigenous and traditional local grapevine varieties into the modern international wine industry.

Concepts: Biology, Vitis vinifera, Wine, Grape, Vitis, Viticulture, Winemaking, Phylloxera

2

Smoke-taint is a wine defect linked to organoleptic volatile phenols (VPs) in Vitis vinifera L. berries that have been exposed to smoke from wildland fires. Herein, the levels of smoke-taint-associated VPs are reported in Cabernet Franc berries from veraison to commercial maturity and in wine after primary fermentation following on-vine exposure to simulated wildland fire smoke. VPs increased after smoke exposure, were rapidly stored as acid-labile conjugates, and the levels of both free VPs and conjugated forms remained constant through ripening to commercial maturity. An increase in total VPs after primary fermentation suggested the existence of VP-conjugates other than the acid-labile VP-glycosides already reported. This conclusion was supported with base hydrolysis on the same samples. Relative to published results, the data suggested a multifactorial regional identity for smoke-taint and they inform efforts to produce a predictive model for perceptible smoke-taint in wine based on the chemical composition of smoke-exposed berries.

Concepts: Vitis vinifera, Wine, Grape, Vitis, Vitaceae, Viticulture, Winemaking, Phylloxera

2

The vascular system of grapevine has been reported as being highly vulnerable, even though grapevine regularly experiences seasonal drought. Stomata would consequently remain open below water potentials that would generate a high loss of stem hydraulic conductivity via xylem embolism. This situation would necessitate daily cycles of embolism repair to restore hydraulic function.. However, a more parsimonious explanation is that some hydraulic techniques are prone to artifacts in species with long vessels, leading to overestimation of vulnerability. The aim of this study was to provide an unbiased assessment of (i) the vulnerability to drought-induced embolism in perennial and annual organs, and (ii) the ability to refill embolized vessels in two Vitis species. X-ray micro-CT observations on intact plants indicated that both V. vinifera and V. riparia were relatively vulnerable, with the pressure inducing 50% loss of stem hydraulic conductivity (Ψ50Stem) = -1.7 and -1.3MPa, respectively. In V. vinifera, both the stem and petiole had similar sigmoidal vulnerability curves, but differed in Ψ50 (-1.7 and -1.0MPa for stem and petiole, respectively). Refilling was not observed as long as bulk xylem pressure remained negative (e.g. at the apical part of the plants): P=-0.11{plus minus}0.02MPa; ∆PLC=0.02{plus minus}0.01%). However, positive xylem pressure was observed at the basal part of the plant (P=0.04{plus minus}0.01MPa), leading to recovered conductance (∆PLC=-0.24{plus minus}0.12%). Our findings provide evidence that grapevine is unable to repair embolized xylem vessels under negative pressure, but its hydraulic vulnerability segmentation provides a significant protection of the perennial stem.

Concepts: Philosophy of science, Annual plant, Grape, Vitis, Vitaceae, Vitis riparia, Perennial plant, Phylloxera

2

Grapevine phylloxera, an insect related to true aphids, is a major historic pest of viticulture only controlled through the selection of resistant rootstocks or through quarantine regulations where grapevine is cultivated own-rooted. Transcriptomic data could help understand the bases of its original life-traits, including a striking case of polyphenism, with forms feeding on roots and forms feeding in leaf-galls. Comparisons with true aphids (for which complete genomes have been sequenced) should also allow to link differences in life-traits of the two groups with changes in gene repertoires or shifts in patterns of expression.

Concepts: DNA, Gene, Genetics, Gene expression, Organism, Genome, RNA, Phylloxera