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Pierce's disease (PD) in grapevine (Vitis vinifera) is caused by the bacterial pathogen Xylella fastidiosa. X. fastidiosa is limited to the xylem tissue and following infection induces extensive plant‐derived xylem blockages, primarily in the form of tyloses. Tylose‐mediated vessel occlusions are a hallmark of PD, particularly in susceptible V. vinifera. We temporally monitored tylose development over the course of the disease to link symptom severity to the level of tylose occlusion and the presence/absence of the bacterial pathogen at fine‐scale resolution. The majority of vessels containing tyloses were devoid of bacterial cells, indicating that direct, localized perception of X. fastidiosa was not a primary cause of tylose formation. In addition, we used X‐ray computed microtomography and machine‐learning to determine that X. fastidiosa induces significant starch depletion in xylem ray parenchyma cells. This suggests that a signalling mechanism emanating from the vessels colonized by bacteria enables a systemic response to X. fastidiosa infection. To understand the transcriptional changes underlying these phenotypes, we integrated global transcriptomics into the phenotypes we tracked over the disease spectrum. Differential gene expression analysis revealed that considerable transcriptomic reprogramming occurred during early PD before symptom appearance. Specifically, we determined that many genes associated with tylose formation (ethylene signalling and cell wall biogenesis) and drought stress were up‐regulated during both Phase I and Phase II of PD. On the contrary, several genes related to photosynthesis and carbon fixation were down‐regulated during both phases. These responses correlate with significant starch depletion observed in ray cells and tylose synthesis in vessels. During Pierce's disease, Xylella fastidiosa triggers transcriptional changes in Vitis vinifera grapevines and induces major physiological responses, including tylose formation and starch depletion.

Aims In 2012, Italian kiwifruit orchards were hit by a serious root disease of unknown aetiology (kiwifruit decline, KD) that still causes extensive damage to the sector. While waterlogging was soon observed to be associated with its outbreak, the putative role of soil microbiota remains unknown. This work investigates the role of these two factors in the onset of the disease. Methods Historical rainfall data were analysed to identify changes that might explain KD outbreak and mimic the flooding conditions required to reproduce the disease in a controlled environment. A greenhouse experiment was thus designed, and vines were grown in either unsterilized (U) or sterilized (S) soil collected from KD-affected orchards, and subjected (F) or not (N) to artificial flooding. Treatments were compared in terms of mortality rate, growth, and tissue modifications. Results KD symptoms were only displayed by FU-treated vines, with an incidence of 90%. Ultrastructural observations detected tyloses and fibrils in the xylem vessels of all plants, irrespective of the treatment. Phytopythium vexans and Phytopythium chamaehyphon , isolated from roots of FU plants, emerged as the associated microorganisms. Conclusions We succeeded in reproducing KD under controlled conditions and confirmed its association with both waterlogging and soil-borne microorganism(s).

Esca disease as well as Botryosphaeria and Eutypa dieback cause considerable economic problems for vineyards worldwide, and currently, no efficient treatment is available to control these diseases. For these three grapevine trunk diseases (GTDs), the main physiological effects reported concern carbohydrate metabolism and defence responses in the different organs of vine. In the trunk, a depletion of starch reserves in woody tissues is associated with fungal colonization; in the leaves, where pathogens are not present, the carbohydrate metabolism is also affected as revealed by a decline of the photosynthetic rate. A consequence of these disturbances is a lower pool of carbon reserves that might contribute to a decrease of plant development and vigour during the subsequent year. Other metabolic activities such as lipid and amino acid metabolism are down regulated. The perturbation of these primary metabolisms is often associated with the induction of defence responses. The development of biochemical barriers resulting from the accumulation of both tyloses and gummosis is observed during the infection of the wood causing blockage of the xylem vessels and thus limiting the fungal invasion. Their progression in the wood is also inhibited by the formation of polyphenol-rich reaction zones and by the accumulation of pathogenesis-related proteins, and the oxidative burst and the production of reactive oxygen species. Additionally, detoxification processes of the vine are involved; this reaction could be linked to the production of extracellular compounds by GTD agents some of which are phytotoxic. As a consequence, the sensory quality of berries and probably the wine made from these berries decrease. This review presents an overview of the physiological modifications described in vines affected by GTDs.

Premise of the Study Xylem vessels transition through different stages during their functional lifespan, including expansion and development of vessel elements, transition to vessel hydraulic functionality, and eventual transition to post‐functionality. We used information on vessel development and function to develop a model of vessel lifespan for woody plants. Methods We examined vessel functional lifespan using repeated anatomical sampling throughout the growing season, combined with active‐xylem staining to evaluate vessel hydraulic transport functionality. These data were combined with a literature review. The transitions between vessel functional lifespans for several species are illustrated, including grapevine (Vitis vinifera L., Vitaceae), English oak (Quercus robur L., Fagaceae), American chestnut [Castanea dentata (Marshall) Borkh.; Fagaceae], and several arid and semi‐arid shrub species. Key Results In intact woody plants, development and maturation of vessel elements may be gradual. Once hydraulically functional, vessel elements connect to form a vessel network that is responsible for bulk hydraulic flow through the xylem. Vessels become nonfunctional due to the formation of gas emboli. In some species and under some conditions, vessel functionality of embolized conduits may be restored through refilling. Blockages, such as tyloses, gels, or gums, indicate permanent losses in hydraulic functional capacity; however, there may be some interesting exceptions to permanent loss of functionality for gel‐based blockages. Conclusions The gradual development and maturation of vessel elements in woody plants, variation in the onset of functionality between different populations of vessels throughout the growing season, and differences in the timing of vessel transitions to post‐functionality are important aspects of plant hydraulic function.

Vascular occlusions are common structural modifications made by many plant species in response to pathogen infection. However, the functional role(s) of occlusions in host plant disease resistance/susceptibility remains controversial. This study focuses on vascular occlusions that form in stem secondary xylem of grapevines (Vitis vinifera) infected with Pierce's disease (PD) and the impact of occlusions on the hosts' water transport and the systemic spread of the causal bacterium Xylella fastidiosa in infected vines. Tyloses are the predominant type of occlusion that forms in grapevine genotypes with differing PD resistances. Tyloses form throughout PD-susceptible grapevines with over 60% of the vessels in transverse sections of all examined internodes becoming fully blocked. By contrast, tylose development was mainly limited to a few internodes close to the point of inoculation in PD-resistant grapevines, impacting only 20% or less of the vessels. The extensive vessel blockage in PD-susceptible grapevines was correlated to a greater than 90% decrease in stem hydraulic conductivity, compared with an approximately 30% reduction in the stems of PD-resistant vines. Despite the systemic spread of X. fastidiosa in PD-susceptible grapevines, the pathogen colonized only 15% or less of the vessels in any internode and occurred in relatively small numbers, amounts much too small to directly block the vessels. Therefore, we concluded that the extensive formation of vascular occlusions in PD-susceptible grapevines does not prevent the pathogen's systemic spread in them, but may significantly suppress the vines' water conduction, contributing to PD symptom development and the vines' eventual death.

Global climate change is accompanied by a change in tree composition in many regions. In Europe, the distribution areas of many species are expanding towards the north so that, among others, black locust ( Robinia pseudoacacia ), which is native to the USA and has long been established in south-eastern Europe, is also becoming increasingly important in central and northern Europe. Many other tree species are known to have different properties between their original and new locations, including the biological durability of the wood. Hence, the resistance of black locust wood against decay fungi was studied concerning origin-specific differences. Wood was sampled from seven different origins in Europe and original habitats in the United States. Fungal incubation experiments were conducted, wood extractives were analysed, and different anatomical characteristics were quantified such as ring width, vessel size distribution and the presence of tyloses. In addition to differences in durability between juvenile and mature wood, origin-specific differences within the mature heartwood were attributed to extractive contents and the percentages of earlywood vessels containing tyloses. Based on parameters that contributed at least 20% to mass loss, susceptibility to fungal decay was modelled with multiple regressions.

The internal temperature of flowers may be higher than air temperature, and warmer nectar could offer energetic advantages for honeybee thermoregulation, as well as being easier to drink owing to its lower viscosity. We investigated the responses of Apis mellifera scutellata (10 colonies) to warmed 10% w/w sucrose solutions, maintained at 20–35°C, independent of low air temperatures, and to 20% w/w sucrose solutions with the viscosity increased by the addition of the inert polysaccharide Tylose (up to the equivalent of 34.5% sucrose). Honeybee crop loads increased with nectar temperature, as did the total consumption of sucrose solutions over 2 h by all bees visiting the feeders. In addition, the preference of marked honeybees shifted towards higher nectar temperatures with successive feeder visits. Crop loads were inversely proportional to the viscosity of the artificial nectar, as was the total consumption of sucrose solutions over 2 h. Marked honeybees avoided higher nectar viscosities with successive feeder visits. Bees thus showed strong preferences for both warmer and less viscous nectar, independent of changes in its sugar concentration. Bees may benefit from foraging on nectars that are warmer than air temperature for two reasons that are not mutually exclusive: reduced thermoregulatory costs and faster ingestion times due to the lower viscosity.

Fusarium oxysporum f. sp. niveum (Fon) is the causative agent of Fusarium wilt disease of watermelon; it is the most serious soil-borne pathogen around the globe. The yield loss is around 30–80% or even more, and is presently a major hindrance to watermelon cultivation worldwide. Initially, the infected watermelon plant shows symptoms like loss of turgor pressure of the leaves and vines that can be recovered at night. The progress of the disease in contaminated transplants turns into dull green to yellow and finally necrotic. When the fungus continues to colonize the xylem vessel, it usually forms more tyloses, finally limiting water movement and causing wilt. The correct identification of the pathogen is necessary for proper disease control. As such, the selection of a molecular marker could serve as an effective means of screening the pathogen. Additionally, different methods have also been reported for the identification of Fon. Therefore, this review focused on the comprehensive description of the biology, diversity, detection, aggressiveness, mycotoxin production, and eco-friendly management strategies of the Fusarium wilt disease of watermelon.

Grapevines require pruning procedures to maintain plant morphology and ensure productivity, and these procedures cause wounds that induce physical and biological host defence mechanisms. Grapevine tissue reactions to wounding resulting from four different pruning methods were assessed. Rapid (immediate) defence reactions were detected in 1-year-old canes with preserved basal buds. Formation of tyloses (≈ 90% of xylem vessels) was observed 1 month later on canes where the basal buds were maintained and no short stubs were left (i.e. the pruning cuts preserved the buds). At 2 months after pruning, lignin was slightly increased in cortical parenchyma after pruning of 3-year-old grapevine wood. Neither callose nor suberin production was observed in healing wounds, as is known in other fruit or broadleaf trees. In 3-year-old canes, fungal hyphae were observed in the non-active wood below the pruning cut surfaces. Preliminary observations of desiccation cones within canes confirmed that the basal buds preserved the canes from desiccation, after comparing different pruning procedures on canes of the same age. After 9 months, the desiccation cones were greater in 3- than 1-year-old wounds.

Background and AimsOur knowledge of tylosis formation is mainly based on observations of extant plants; however, its developmental and functional significance are less well understood in fossil plants. This study, for the first time, describes a complete tylosis formation in a fossil woody conifer and discusses its ecophysiological implications.MethodsThe permineralized stem of Shenoxylon mirabile was collected from the upper Permian (Changhsingian) Sunjiagou Formation of Shitanjing coalfield, northern China. Samples from different portions of the stem were prepared by using the standard thin-sectioning technique and studied in transmitted light.Key ResultsThe outgrowth of ray parenchyma cells protruded into adjacent tracheids through pits initially forming small pyriform or balloon-shaped structures, which became globular or slightly elongated when they reached their maximum size. The tracheid luminae were gradually occluded by densely spaced tyloses. The host tracheids are arranged in distinct concentric zones representing different growth phases of tylosis formation within a single growth ring.ConclusionsThe extensive development of tyloses from the innermost heartwood (metaxylem) tracheids to the outermost sapwood tracheids suggests that the plant was highly vulnerable and reacted strongly to environmental stress. Based on the evidence available, the tyloses were probably not produced in response to wound reaction or pathogenic infection, since evidence of wood traumatic events or fungal invasion are not recognizable. Rather, they may represent an ecophysiological response to the constant environmental stimuli.