Canopy Architectural Characteristics of Ten New Olive (Olea europaea L.) Genotypes and Their Potential for Cultivation in Super-High-Density Orchards.

In recent years, there has been growing interest in olive genotypes (Olea europaea L.) suitable for super-high-density (SHD > 1200 trees/hectare) orchards. To date, only a few cultivars are considered fitting for such cultivation system. In this study, the first results on the architectural characteristics of the canopy of ten new olive genotypes are presented. Their suitability for SHD orchards was evaluated and compared with the cultivar 'Arbequina', which is considered suitable for SHD olive orchards and, for this reason, was used as the control. Several canopy measurements were taken, and some architectural parameters, such as branching frequency, branching density, and branch diameter/stem diameter ratio were calculated. The branching frequency value was greater than 0.20 in 'Arbequina' and in only four of the genotypes. The branching density in five genotypes was similar to 'Arbequina'. 'Arbequina' had the lowest value for the branch diameter/stem diameter ratio, and only three genotypes had similar values. These initial results showed that only one genotype has all canopy architectural characteristics comparable to those of the cv. 'Arbequina'. Further studies are needed to evaluate the production traits of these new genotypes and complete their characterization.

Dodine an effective alternative to copper for controlling Venturia oleaginea, the causal agent of pea-cock eye disease, in highly infected olive trees.

A trial was carried out in central Italy in an olive orchard of cultivar Moraiolo, highly infected by Venturia oleaginea. The aim of the investigation was to evaluate the effects of autumn and spring applications of copper oxychloride or dodine to control the disease. Non treated trees were used as the control. The effects of the fungal attacks on leaves and inflorescence development confirmed the high susceptibility of the cultivar Moraiolo to the disease. The results show that in trees heavily infected, but with most of the infected leaves at the early stage of the disease (asymptomatic phase), treatments with dodine had a curative effect, with consequent reduction in the appearance of symptomatic leaves and defoliation with respect to the control or copper-treated trees. The use of dodine against the autumnal attacks of V. oleaginea allowed most of the old leaves to be maintained until the new ones had formed, which is important for the growth processes during the early part of the growing season. Overall, the results indicate that to efficiently control the pathogen using copper compounds, treatments must start soon after the beginning of the attack and be repeated in order to maintain the infection at a low level. Dodine can be efficiently used if there is a great increase in infected leaves. The use of dodine to solve particular situations and not for normal repeated use is regulated by the fact that in some countries, Italy included, protocols for integrated pest management allow only one dodine treatment/year.

No- or Low-Content Copper Compounds for Controlling Venturia oleaginea, the Causal Agent of Olive Leaf Spot Disease.

The efficacy of using a synthetic (azoxystrobin + difenoconazole), copper-based (copper oxychloride) and low-content copper compound (copper complexed with gluconate and lignosulphonate) fungicides for controlling Venturia oleaginea, the causal agent of olive spot disease, was evaluated in an olive (cv. Nabali) orchard located in the Kafr Qud area (Palestine) in 2017-2018. Treatments were applied at three different times (February, April, and August). In January 2017, at the beginning of the experiment, about 90% of the leaves grown in 2016 were infected. Defoliation was determined by counting the leaves on the labeled branches initially and then periodically. It increased gradually in both the control and treated trees, but those treated with azoxystrobin + difenoconazole or with copper complexed with gluconate and lignosulphonate showed a slower defoliation rate. During 2017, new shoots grew and new leaves developed. All treatments reduced the drop of new leaves with respect to the control, with positive effects on the reproductive activity (inflorescence growth and yield). Overall, all treatments significantly reduced the disease, thus indicating the possibility of greatly reducing infections if treatments are regularly applied each year, also with traditional (copper-based) fungicides. Due to their capability of penetrating inside the vegetative tissue, azoxystrobin + difenoconazole or copper complexed with gluconate and lignosulphonate reduced/slowed down the drop of infected leaves. The use of these fungicides is therefore particularly recommended when olive leaf spot disease is severe. The use of low-content copper compounds allows the amount of metallic copper used for the treatments against V. oleaginea to be greatly reduced.

Cultivar ideotype for intensive olive orchards: plant vigor, biomass partitioning, tree architecture and fruiting characteristics.

In order to achieve higher and earlier yield, modern olive orchards are increasingly intensified, with tree densities up to > 1500 trees hectare-1. With increasing tree densities, individual-tree canopy volume must be proportionally reduced. Not all cultivars are adaptable to high and very high orchard densities, because of excessive vigor and/or insufficient bearing when the canopy is pruned to a small volume. However, what makes an olive cultivar suitable for intensive and super intensive orchards is not clear. Recently, few studies have addressed this topic, suggesting that tree architecture and early bearing are essential traits. Yet, what architectural and productive features are important, how they work and whether they are interrelated remains elusive. This review summarizes and interprets the literature on olive, as well as the more abundant literature available for other fruit species, aiming to provide a comprehensive knowledge framework for understanding how tree architectural characteristics, plant vigor, and fruiting vary across olive genotypes, and how they are interconnected. It is concluded that, among the architectural characteristics, greater branching and smaller diameters of woody structures are particularly important features for cultivar suitability to intensive and super intensive olive orchards. Greater branching allows to produce more fruiting sites in the small volume of canopy allowed in these systems. It also reduces investments in woody structures, liberating resources for fruiting. Additional resources are liberated with smaller structure diameters. Greater branching also increases resources by increasing biomass partitioning into leaves (i.e. the photosynthetic organs), relative to wood. Since yield is affected by the competition for resources with vegetative growth, reducing resource investments in woody structures and/or increasing resource directly, increases yield. Yield, in turn, depresses vegetative growth, reducing vigor and the need for pruning. High yields also produce short shoots which have relatively greater investments in leaf mass and area, and lower in the woody stem, making them more suitable than long shoots to support concurrent fruit growth. This single framework of interpretation of how the different architectural and fruiting characteristics work and interact with one-another, will provide guidance for cultivar selection and breeding for intensive and super intensive olive orchards.

From flower to fruit: fruit growth and development in olive (Olea europaea L.)-a review.

The olive (Olea europaea L.) is the most cultivated tree crop in the Mediterranean and among the most cultivated tree crops worldwide. Olive yield is obtained by the product of fruit number and fruit size; therefore, understanding fruit development, in terms of both number and size, is commercially and scientifically relevant. This article reviews the literature on fruit development, from the flower to the mature fruit, considering factors that affect both fruit size and number. The review focuses on olive but includes literature on other species when relevant. The review brings the different factors affecting different phases of fruit development, addressed separately in the literature, under a single frame of interpretation. It is concluded that the different mechanisms regulating the different phases of fruit development, from pistil abortion to fruit set and fruit size, can be considered as different aspects of the same overall strategy, that is, adjusting fruit load to the available resources while striving to achieve the genetically determined fruit size target and the male and female fitness targets.

Characterization of Olive Fruit Damage Induced by Invasive Halyomorpha halys.

The brown marmorated stink bug, Halyomorpha halys (Stål), is an invasive species causing economic crop losses. This species was recently detected attacking olive fruits. The aim of this study was to characterize feeding damage. Olive samples were initially collected from a field where H. halys was reported to cause damage to olive fruits. Hence, we conducted a field trial on the Moraiolo variety using sleeve cages to test the effect of H. halys feeding pressure on olive fruit drop and evaluated the effect of feeding on fruit quality. We tested two densities of H. halys (two or eight adults/cage) at two different stages of olive development, pre- and post-pit hardening. High pressure of H. halys before pit hardening caused a significant fruit drop compared to the control. In addition, chemical analysis of damaged and infested fruits revealed higher levels of total phenols compared to healthy fruits. These findings indicate that feeding by H. halys induced a stress response in the plants that could translate in quality variations in the olive drupes.

The Ancient Olive Trees (Olea europaea L.) of the Maltese Islands: A Rich and Unexplored Patrimony to Enhance Oliviculture.

A prospecting campaign in the Maltese Islands has ensured the survival of several ancient olive trees (Olea europaea L.), genetically distant from known cultivars. Most of these plants were abandoned or partially cultivated. A two-year evaluation of fruit characteristics and compositions was performed on samples collected from the main representatives of these indigenous genotypes. Analyses were carried out using Gas Chromatography, High-Performance Liquid Chromatography and Near Infrared Spectrometry. Among the fruit samples, a wide range of variations was observed. Some of the genotypes showed fruit traits suitable for table olive production. This is the case of samples with a pulp/pit ratio higher than four, such as 1Wardija, 1Caritas, 1Plattini, 1Bingemma Malta and 3Loretu, whilst 1Bidni, 1Mellieha, 2Qnotta, 3Loretu, 1Bingemma Malta and 1Caritas were suitable for dual purpose. The total phenol content ranged from 6.3 (1Wardija) to 117.9 (2Mtarfa) g/kg of fresh pulp. The average percentage of MUFA was quite low for most of the varieties. These genotypes, which presumably originated in the Maltese Islands and are well adapted to the local pedo-climatic conditions, are being propagated for the following evaluation of their bio-agronomical performance (production, suitability to intensive cultivation, environmental sustainability, product quality, etc.). The purpose is to select, among these local genotypes, the most outstanding varieties, in terms of phenolic and FA profile and agronomical potential, to spread into cultivation, thereby contributing to an increase in the quality of the local table and olive oil production, strongly linked to the territory.

Neem Oil to Reduce Zeatin Use and Optimize the Rooting Phase in Olea europaea L. Micropropagation.

Micropropagation is an in vitro propagation technique, established in the nursery field sector for numerous species, which offers several advantages compared to traditional agamic propagation techniques. In the case of the olive tree, however, despite the advances made through research, it is still little used, due to the recalcitrance to in vitro proliferation and/or rooting of many olive cultivars and the high cost of zeatin, the only cytokinin that makes it possible to achieve a satisfactory proliferation rate in this species. In this context, numerous attempts have been made to identify alternative cytokinin compounds able to improve the proliferation rate of olive tree explants and thus reduce the unitary production cost. In particular, there is a growing interest in the use of natural substances (called in some cases "complex mixtures"), which, when added to the in vitro cultivation substrates, seem to be able to improve proliferation rates. In the present study, neem oil was added to the propagation substrates (partially/totally replacing zeatin) and in the rooting phase for the olive cultivar Moraiolo. In particular, in the proliferation phase, the effect of neem oil (0.1 mL L-1) in substrates containing different zeatin concentrations (0, 1, 2, and 4 mg L-1) was evaluated. For the rooting phase, agarized substrate and soil were used with shoots derived from a standard proliferation substrate (4 mg L-1 zeatin) and from the substrate that gave the best results in the proliferation phase (2 mg L-1 zeatin and 0.1 mL L-1 neem oil). In the proliferation phase, the addition of neem oil in the substrates with low zeatin concentration (1 and 2 mg L-1) induced an increase in the number of adventitious shoots and shoots length. On the contrary, the addition of neem oil in the rooting substrates did not positively influence the rooting phase, but positive results especially in terms of root number and length were observed in explants derived from a neem oil-enriched proliferation substrate compared to the control substrate. Therefore, the present study demonstrated for the first time the positive role of neem oil in the proliferation of olive in vitro with low zeatin concentrations.

Field and Laboratory Efficacy of Low-Impact Commercial Products in Preventing Olive Fruit Fly, Bactrocera oleae, Infestation.

The olive fruit fly, Bactrocera oleae, is the key pest of olive trees in several areas of the world. Given the need for the development of sustainable control methods, preventive tools, based on the manipulation of pest behaviour, must be considered. Here, under field and laboratory conditions, we tested the efficacy of different products in preventing B. oleae infestation. A field trial was conducted, from July to November 2020, in an olive orchard located in Central Italy. A table olive variety was selected and sprayed with rock powder, propolis, the mixture of both, copper oxychloride, or water (control). All treatments, except propolis, caused a reduction of B. oleae oviposition in olives, compared to the control. The mixture allowed the strongest reduction of fly infestation throughout the season, suggesting a synergistic effect. Behavioural no-choice assays were conducted to better understand the effects of treatments on B. oleae females. Compared to the control, females showed a lower preference for the central area of an arena containing an olive twig bearing two olive fruits, fully developed, but still green, treated with rock powder, plus propolis mixture. For all treatments, B. oleae showed lower oviposition events, suggesting deterrence to oviposition. Our results indicate that the tested products may have value against B. oleae, within integrated pest management (IPM) and organic agriculture.

Agronomic potential of two different glass-based materials as novel inorganic slow-release iron fertilizers.

BACKGROUND: Large amounts of chemical fertilizers are still currently used to compensate the soil nutrients scarcity in order to increase and sustain crop yield with consequent rising of environmental pollution and health problems. To mitigate these environmental risks, fertilizers with slow-release behaviours have been developed. The aim of this study was to assess the agronomic potential of two different glass-based materials (by-products from the ceramic sector) as inorganic slow-release iron (Fe) fertilizers. RESULTS: The X-ray powder diffraction confirmed the presence of amorphous structure and the richness in Fe of the investigated materials. The solubility analysis highlighted the slow Fe release from the glassy network and that the maximum of the Fe release was at alkaline pH suggesting their potential use as slow-release Fe fertilizers, especially in calcareous soils. The pot and leaching experiments demonstrated that although the glass-based materials increased the amount of soil available Fe, we did not observe Fe leaching and plant toxicity. This fact would suggest their reliability to increase soil fertility without negative effects on the environment. CONCLUSION: The use of glass-based materials, specifically by-products from the ceramic sectors, as inorganic slow-release Fe fertilizers can be sustained. The tests performed at three different pH conditions testified the slow-release behaviour of the tested materials and underlined that the Fe release increases at alkaline environment. Therefore, the present study pointed out the glass-based materials by products from the ceramic sector as novel slow-release and environmental-friendly fertilizers in agriculture. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Carbon allocation strategies and water uptake in young grafted and own-rooted hazelnut (Corylus avellana L.) cultivars.

In this study, grafted and own-rooted young hazelnut plants of three high-quality cultivars were cultivated in Central Italy to investigate possible differences in growth, fruit and flower production, and physiological processes encompassing water uptake, photosynthetic variables and non-structural carbohydrate allocation. Stable isotopes and photosynthetic measurements were used to study carbon and water fluxes in plants. For the first time, an ecophysiological study was carried out to understand the seasonal growth dynamics of grafted plants in comparison with own-rooted plants. The own-rooted hazelnuts showed rapid above-ground development with large canopy volume, high amount of sprouts and earlier yield. The grafted plants showed greater below-ground development with lower canopy volumes and lower yield. However, later, the higher growth rates of the canopy led these plants to achieve the same size as that of the own-rooted hazelnuts and to enter the fruit production phase. Different seasonal behaviour in root water uptake and leaf photosynthesis-related variables was detected between the two types of plants. The grafted plants showed root development that allowed deeper water uptake than that of the own-rooted hazelnuts. Moreover, the grafted plants were characterized by a higher accumulation of carbohydrate reserves in their root tissues and by higher stomatal reactivity, determining significant plasticity in response to seasonal thermal variations.

Olive leaf spot caused by Venturia oleaginea: An updated review.

Olive leaf spot (OLS) caused by Venturia oleaginea is widespread in all olive-growing areas and continents, where can cause severe yield losses. The disease is often underestimated for the difficulty to reveal early leaf symptoms and for the pathogen-induced phylloptosis, which creates the illusion of healthy and restored plants. The present review provide updated information on taxonomy, pathogen life style and cycle, epidemiology, diagnosis, and control. Application of copper-based fungicides is the main method to control OLS. However, the regulation 2009/1107 of the European Commission include these fungicides in the list of substances candidates for substitution. It is therefore urgent to find alternative control strategies especially for organic agriculture. Among new approaches/strategies for controlling OLS, promising results have been obtained using nanotechnology, endophytic microbes, and biostimulants.

Modifications of Grapevine Berry Composition Induced by Main Viral and Fungal Pathogens in a Climate Change Scenario.

The grapevine is subject to high number of fungal and viral diseases, which are responsible for important economic losses in the global wine sector every year. These pathogens deteriorate grapevine berry quality either directly via the modulation of fruit metabolic pathways and the production of endogenous compounds associated with bad taste and/or flavor, or indirectly via their impact on vine physiology. The most common and devastating fungal diseases in viticulture are gray mold, downy mildew (DM), and powdery mildew (PM), caused, respectively by Botrytis cinerea, Plasmopara viticola, and Erysiphe necator. Whereas B. cinerea mainly infects and deteriorates the ripening fruit directly, deteriorations by DM and PM are mostly indirect via a reduction of photosynthetic leaf area. Nevertheless, mildews can also infect berries at certain developmental stages and directly alter fruit quality via the biosynthesis of unpleasant flavor compounds that impair ultimate wine quality. The grapevine is furthermore host of a wide range of viruses that reduce vine longevity, productivity and berry quality in different ways. The most widespread virus-related diseases, that are known nowadays, are Grapevine Leafroll Disease (GLRD), Grapevine Fanleaf Disease (GFLD), and the more recently characterized grapevine red blotch disease (GRBD). Future climatic conditions are creating a more favorable environment for the proliferation of most virus-insect vectors, so the spread of virus-related diseases is expected to increase in most wine-growing regions. However, the impact of climate change on the evolution of fungal disease pressure will be variable and depending on region and pathogen, with mildews remaining certainly the major phytosanitary threat in most regions because their development rate is to a large extent temperature-driven. This paper aims to provide a review of published literature on most important grapevine fungal and viral pathogens and their impact on grape berry physiology and quality. Our overview of the published literature highlights gaps in our understanding of plant-pathogen interactions, which are valuable for conceiving future research programs dealing with the different pathogens and their impacts on grapevine berry quality and metabolism.

A Dual-Successive-Screen Model at Pollen/Stigma and Pollen Tube/Ovary Explaining Paradoxical Self-Incompatibility Diagnosis in the Olive Tree-An Interpretative Update of the Literature.

The 'pollen test' and 'fruit set test' following controlled crossing combinations of parents are the most commonly used methods for pollination incompatibility studies in Olea europaea L. Self-incompatibility (SI), with diagnoses based on the pollen test and pollen germination, indicating self-compatibility, is not always followed by fruit set in this species. To solve this dispute, we have reconciled all observations into a new model. Mismatches between field and laboratory data and between methods are resolved by the dual-successive-screen model (DSSM) supposing two different loci for the expression of the two SI mechanisms. Pollen/stigma is controlled by diallelic SI, or DSI, inferring two G1 and G2 compatibility/incompatibility (C/I) groups for varieties, whereas pollen tubes in ovaries are controlled by poly-allelic SI or PASI with twenty C/I groups. To explain the selfing of varieties, we have suggested that some determinants in the pollen tube and stigma are unstable and degrade (DS-D for degradation of S-determinant) after three to five days, enabling some pollen tubes to avoid being rejected, hence reaching ovules. DSI and PASI in the DSSM and DS-D mechanisms, plus the andromonoecy of the olive tree, complexify SI studies. Inferences from DSSM and DS-D mechanisms in olive orchard practice are detailed.

Gluconeogenesis in Plants: A Key Interface between Organic Acid/Amino Acid/Lipid and Sugar Metabolism.

Gluconeogenesis is a key interface between organic acid/amino acid/lipid and sugar metabolism. The aims of this article are four-fold. First, to provide a concise overview of plant gluconeogenesis. Second, to emphasise the widespread occurrence of gluconeogenesis and its utilisation in diverse processes. Third, to stress the importance of the vacuolar storage and release of Krebs cycle acids/nitrogenous compounds, and of the role of gluconeogenesis and malic enzyme in this process. Fourth, to outline the contribution of fine control of enzyme activity to the coordinate-regulation of gluconeogenesis and malate metabolism, and the importance of cytosolic pH in this.

The First Evidence of the Beneficial Effects of Se-Supplementation on In Vitro Cultivated Olive Tree Explants.

Selenium is an essential micronutrient that provides important benefits to plants and humans. At proper concentrations, selenium increases plant growth, pollen vitality, the shelf life of fresh products, and seems to improve stress resistance; these effects can certainly be attributed to its direct and indirect antioxidant capacity. For these reasons, in the present work, the effects of selenium at different dosages on in vitro cultivated olive explants were investigated to observe possible positive effects (in terms of growth and vigor) on the proliferation phase. The work was carried out on four different olive cultivars: "San Felice", "Canino", "Frantoio", and "Moraiolo". The explants were cultured in aseptic conditions on olive medium (OM), with the addition of 4 mg·L-1 of zeatin, 30 g·L-1 of sucrose, and 7 g·L-1 of agar. The experimental scheme included a comparison between explants grown with five different concentrations of Na2SeO4 (0, 10, 20, 40, and 80 mg L-1) added to the medium during three successive subcultures. Interesting information has emerged from the results and all varieties responded to different concentrations of Selenium. The optimal Se dosages varied for each cultivar, but in general, Se concentration between 10 and 40 mg L-1 increased fresh and dry weight of the explants and shoot lengths. Se treatment induced in all cultivars and for all dosages used an increase in total Se content in proliferated explants. Furthermore, as the subcultures proceeded, the ability of the explants to absorb Se did not diminish. The Se content ranged from 8.55 to 114.21 µg kg-1 plant DW in 'Frantoio', from 9.83 to 94.85 µg kg-1 plant DW in 'Moraiolo', from 19.84 to 114.21 µg kg-1 plant DW in 'Canino', and from 20.97 to 95.54 µg kg-1 plant DW in 'San Felice'. In general, the effect of selenium tends to decrease with the progress of subcultures and this suggests a sort of "adaptation" effect of the explants to its presence. The present study highlights for the first time the possibility of using in vitro cultures as biotechnological support to study supplementation with selenium and its effects on in vitro olive plant growth.

Sucrose Metabolism and Transport in Grapevines, with Emphasis on Berries and Leaves, and Insights Gained from a Cross-Species Comparison.

In grapevines, as in other plants, sucrose and its constituents glucose and fructose are fundamentally important and carry out a multitude of roles. The aims of this review are three-fold. First, to provide a summary of the metabolism and transport of sucrose in grapevines, together with new insights and interpretations. Second, to stress the importance of considering the compartmentation of metabolism. Third, to outline the key role of acid invertase in osmoregulation associated with sucrose metabolism and transport in plants.

Effects of cultivar, fruit presence and tree age on whole-plant dry matter partitioning in young olive trees.

This study investigated the effects of cultivar, fruit presence and tree age on whole-plant partitioning of dry matter and energy equivalents (i.e., glucose equivalents). Young trees of two cultivars characterized by different vigor (i.e., Arbequina, low vigor and Frantoio, high vigor) were either completely deflowered from 2014 to 2017 or never, providing two contrasting levels of cumulated reproductive growth over the following 4 years. Total vegetative dry matter growth over the 4 years was assessed by destructive samplings (whole tree). Plant growth was inversely correlated to reproductive efforts, with Arbequina producing more and growing less than Frantoio. Deflowered trees grew similarly across cultivars, although deflowered Arbequina grew statistically less than deflowered Frantoio by the fourth year, due to abundant flower production. Total reproductive (flowers + fruit) and vegetative biomass production were the same for all cultivars and treatments. Arbequina had a greater distribution of dry matter in directly productive structures (current and one-year-old shoots) and in leaves. This allows it to increase the number of current and following-year production sites, and to save in the resources invested in non-productive sinks (roots, trunk and branches), thus liberating resources for reproductive growth. Greater investments in leaves allow it to intercept more light and thus to increase assimilation. Increased assimilation and increased partitioning towards productive structures, and decreased competition by non-productive structures might contribute to explain the greater early bearing attitude of this cultivar.

Grape Berry Secondary Metabolites and Their Modulation by Abiotic Factors in a Climate Change Scenario-A Review.

Temperature, water, solar radiation, and atmospheric CO2 concentration are the main abiotic factors that are changing in the course of global warming. These abiotic factors govern the synthesis and degradation of primary (sugars, amino acids, organic acids, etc.) and secondary (phenolic and volatile flavor compounds and their precursors) metabolites directly, via the regulation of their biosynthetic pathways, or indirectly, via their effects on vine physiology and phenology. Several hundred secondary metabolites have been identified in the grape berry. Their biosynthesis and degradation have been characterized and have been shown to occur during different developmental stages of the berry. The understanding of how the different abiotic factors modulate secondary metabolism and thus berry quality is of crucial importance for breeders and growers to develop plant material and viticultural practices to maintain high-quality fruit and wine production in the context of global warming. Here, we review the main secondary metabolites of the grape berry, their biosynthesis, and how their accumulation and degradation is influenced by abiotic factors. The first part of the review provides an update on structure, biosynthesis, and degradation of phenolic compounds (flavonoids and non-flavonoids) and major aroma compounds (terpenes, thiols, methoxypyrazines, and C13 norisoprenoids). The second part gives an update on the influence of abiotic factors, such as water availability, temperature, radiation, and CO2 concentration, on berry secondary metabolism. At the end of the paper, we raise some critical questions regarding intracluster berry heterogeneity and dilution effects and how the sampling strategy can impact the outcome of studies on the grapevine berry response to abiotic factors.

Biosynthesis and Cellular Functions of Tartaric Acid in Grapevines.

Tartaric acid (TA) is an obscure end point to the catabolism of ascorbic acid (Asc). Here, it is proposed as a "specialized primary metabolite", originating from carbohydrate metabolism but with restricted distribution within the plant kingdom and lack of known function in primary metabolic pathways. Grapes fall into the list of high TA-accumulators, with biosynthesis occurring in both leaf and berry. Very little is known of the TA biosynthetic pathway enzymes in any plant species, although recently some progress has been made in this space. New technologies in grapevine research such as the development of global co-expression network analysis tools and genome-wide association studies, should enable more rapid progress. There is also a lack of information regarding roles for this organic acid in plant metabolism. Therefore this review aims to briefly summarize current knowledge about the key intermediates and enzymes of TA biosynthesis in grapes and the regulation of its precursor, ascorbate, followed by speculative discussion around the potential roles of TA based on current knowledge of Asc metabolism, TA biosynthetic enzymes and other aspects of fruit metabolism.