Harvesting Maturity Assessment of Newly Developed Citrus Hybrids (Citrus maxima Merr. × Citrus sinensis (L.) Osbeck) for Optimum Juice Quality.

The assessment of the optimum harvesting stage is a prerequisite to evaluating the performance of new citrus genotypes. The intrinsic and extrinsic fruit quality traits of citrus fruits change throughout their developmental process; therefore, to ensure the highest quality, the fruit must be harvested at an appropriate stage of maturity. The biochemical changes in terms of total soluble solids (TSS), titratable acidity (TA), TSS/TA ratio, BrimA (Brix minus acidity), and ascorbic acid, in addition to the organoleptic acceptability of 16 new interspecific citrus hybrids, were evaluated in New Delhi (India) during the H1-H8 harvesting stage at 15-day intervals to standardize the optimum harvesting stage. The TA and ascorbic acid content were at a maximum level during the early harvesting stage and declined with time, reaching the minimum level in the last harvesting stage. The TSS, TSS/TA ratio, and BrimA values were found to have an increasing trend up to the last stage in most of the hybrids. The juice content shows an inclining trend during the initial harvesting observations, followed by stable juice content and then a decline. The BrimA was found to be a better predictor for consumer acceptability compared to the traditional maturity index TSS/TA ratio and, thus, harvesting maturity. Specific TSS, TA, and BrimA values, in addition to the juice percentage and ascorbic acid content, corresponding to the highest hedonic score, were judged as the optimum harvesting stage indicators for an individual hybrid genotype. Among the interspecific hybrids, SCSH-9-10/12, SCSH-11-15/12, and SCSH-17-19/13 were found to be superior, having better juice acceptability organoleptic scores (≥6.0) and higher juice content (≥40%). Principal component analysis based on fruit physico-chemical traits could be able to distinguish the optimum maturity stage in all of the citrus genotypes.

Guard cell activity of PIF4 and HY5 control transpiration.

Whole-plant transpiration, controlled by plant hydraulics and stomatal movement, is regulated by endogenous and environmental signals, with the light playing a dominant role. Stomatal pore size continuously adjusts to changes in light intensity and quality to ensure optimal CO2 intake for photosynthesis on the one hand, together with minimal water loss on the other. The link between light and transpiration is well established, but the genetic knowledge of how guard cells perceive those signals to affect stomatal conductance is still somewhat limited. In the current study, we evaluated the role of two central light-responsive transcription factors; a bZIP-family transcription factor ELONGATED HYPOCOTYL5 (HY5) and the basic helix-loop-helix (BHLH) transcription factor PHYTOCHROME INTERACTING FACTOR4 (PIF4), in the regulation of steady-state transpiration. We show that overexpression of PIF4 exclusively in guard cells (GCPIF4) decreases transpiration, and can restrain the high transpiration of the pif4 mutant. Expression of HY5 specifically in guard cells (GCHY5) had the opposite effect of enhancing transpiration rates of WT- Arabidopsis and tobacco plants and of the hy5 mutant in Arabidopsis. In addition, we show that GCHY5 can reverse the low transpiration caused by guard cell overexpression of the sugar sensor HEXOKINASE1 (HXK1, GCHXK), an established low transpiring genotype. Finally, we suggest that the GCHY5 reversion of low transpiration by GCHXK requires the auto-activation of the endogenous HY5 in other tissues. These findings support the existence of an ongoing diurnal regulation of transpiration by the light-responsive transcription factors HY5 and PIF4 in the stomata, which ultimately determine the whole-plant water use efficiency.

Effects of packinghouse operations on the flavor of 'Orri' mandarins.

Mandarins have a delicate flavor and are easy to peel and easy to consume. However, they are relatively perishable and suffer from flavor deterioration after harvest. The goal of the current study was to examine the effects of commercial packinghouse operations on the flavor of 'Orri' mandarins. For that purpose, we collected fruit from four different points along a commercial citrus packing line: (1) directly from the harvest bin, (2) after application of a hot (53°C) fungicide treatment for 30 s, (3) after waxing, and (4) after waxing and after the fruit had passed through a hot-air drying tunnel (37°C) for 2 min. The collected fruit were stored for 3 or 6 weeks at 5°C and then kept for five more days under shelf-life conditions at 22°C. The observed results indicate that the hot fungicide treatment had no effect on flavor quality. However, the waxing and waxing +drying treatments resulted in significant increases in ethanol accumulation, lower flavor-acceptability scores, and increased off-flavors. Gas-chromatography mass-spectrometry (GC-MS) analysis revealed that the waxing and waxing +drying treatments resulted in particular increases in the levels of alcohol and ethyl ester volatiles; whereas levels of other aroma volatiles (i.e., esters, aldehydes, monoterpenes, and sesquiterpenes) decreased after storage in all fruit samples. Overall, the waxing process in commercial citrus packinghouses increased ethanol and ethyl ester volatile levels and harmed flavor acceptability. These findings demonstrate the need to identify new wax formulations that do not hamper fruit-flavor quality.

Sucrose Synthase and Fructokinase Are Required for Proper Meristematic and Vascular Development.

Sucrose synthase (SuSy) and fructokinase (FRK) work together to control carbohydrate flux in sink tissues. SuSy cleaves sucrose into fructose and UDP-glucose; whereas FRK phosphorylates fructose. Previous results have shown that suppression of the SUS1,3&4 genes by SUS-RNAi alters auxin transport in the shoot apical meristems of tomato plants and affects cotyledons and leaf structure; whereas antisense suppression of FRK2 affects vascular development. To explore the joint developmental roles of SuSy and FRK, we crossed SUS-RNAi plants with FRK2-antisense plants to create double-mutant plants. The double-mutant plants exhibited novel phenotypes that were absent from the parent lines. About a third of the plants showed arrested shoot apical meristem around the transition to flowering and developed ectopic meristems. Use of the auxin reporter DR5::VENUS revealed a significantly reduced auxin response in the shoot apical meristems of the double-mutant, indicating that auxin levels were low. Altered inflorescence phyllotaxis and significant disorientation of vascular tissues were also observed. In addition, the fruits and the seeds of the double-mutant plants were very small and the seeds had very low germination rates. These results show that SUS1,3&4 and FRK2 enzymes are jointly essential for proper meristematic and vascular development, and for fruit and seed development.

Root-Associated Microbiomes, Growth and Health of Ornamental Geophytes Treated with Commercial Plant Growth-Promoting Products.

The microbial community inhabiting a plant's root zone plays a crucial role in plant health and protection. To assess the ability of commercial plant growth-promoting products to enhance the positive effects of this environment, two products containing beneficial soil bacteria and a product containing plant extracts were tested on Zantedeschia aethiopica and Ornithogalum dubium. The products were tested in two different growing media: a soil and a soilless medium. The effects of these products on Pectobacterium brasiliense, the causal agent of soft rot disease, were also evaluated in vitro, and on naturally occurring infections in the greenhouse. The growing medium was found to have the strongest effect on the microbial diversity of the root-associated microbiome, with the next-strongest effect due to plant type. These results demonstrate that either a single bacterial strain or a product will scarcely reach the level that is required to influence soil microbial communities. In addition, the microbes cultured from these products, could not directly inhibit Pectobacterium growth in vitro. We suggest density-based and functional analyses in the future, to study the specific interactions between plants, soil type, soil microbiota and relevant pathogens. This should increase the effectiveness of bio-supplements and soil disinfestation with natural products, leading to more sustainable, environmentally friendly solutions for the control of bacterial plant diseases.

Water Deficiency and Induced Defense Against a Generalist Insect Herbivore in Desert and Mediterranean Populations of Eruca sativa.

In natural and agricultural ecosystems, plants are often simultaneously or sequentially exposed to combinations of stressors. Here we tested whether limited water availability (LWA) affects plant response to insect herbivory using two populations of Eruca sativa from desert and Mediterranean habitats that differ in their induced defenses. Considering that such differences evolved as responses to biotic and possibly abiotic stress factors, the two populations offered an opportunity to study ecological aspects in plant response to combined stresses. Analysis of chemical defense mechanisms showed that LWA significantly induced total glucosinolate concentrations in the Mediterranean plants, but their concentrations were reduced in the desert plants. However, LWA, with and without subsequent jasmonate elicitation, significantly induced the expression of proteinase inhibitor in the desert plants. Results of a no-choice feeding experiment showed that LWA significantly increased desert plant resistance to Spodoptera littoralis larvae, whereas it did not affect the relatively strong basal resistance of the Mediterranean plants. LWA and subsequent jasmonate elicitation increased resistance against the generalist insect in Mediterranean plants, possibly due to both increased proteinase inhibitor expression and glucosinolate accumulation. The effect of LWA on the expression of genes involved in phytohormone signaling, abscisic acid (ABA-1) and jasmonic acid (AOC1), and the jasmonate responsive PDF1.2, suggested the involvement of abscisic acid in the regulation of defense mechanisms in the two populations. Our results indicate that specific genotypic responses should be considered when estimating general patterns in plant response to herbivory under water deficiency conditions.

Guard cells control hypocotyl elongation through HXK1, HY5, and PIF4.

The hypocotyls of germinating seedlings elongate in a search for light to enable autotrophic sugar production. Upon exposure to light, photoreceptors that are activated by blue and red light halt elongation by preventing the degradation of the hypocotyl-elongation inhibitor HY5 and by inhibiting the activity of the elongation-promoting transcription factors PIFs. The question of how sugar affects hypocotyl elongation and which cell types stimulate and stop that elongation remains unresolved. We found that overexpression of a sugar sensor, Arabidopsis hexokinase 1 (HXK1), in guard cells promotes hypocotyl elongation under white and blue light through PIF4. Furthermore, expression of PIF4 in guard cells is sufficient to promote hypocotyl elongation in the light, while expression of HY5 in guard cells is sufficient to inhibit the elongation of the hy5 mutant and the elongation stimulated by HXK1. HY5 exits the guard cells and inhibits hypocotyl elongation, but is degraded in the dark. We also show that the inhibition of hypocotyl elongation by guard cells' HY5 involves auto-activation of HY5 expression in other tissues. It appears that guard cells are capable of coordinating hypocotyl elongation and that sugar and HXK1 have the opposite effect of light on hypocotyl elongation, converging at PIF4.

Direct Binding of Salicylic Acid to Pectobacterium N-Acyl-Homoserine Lactone Synthase.

Salicylic acid (SA) is a hormone that mediates systemic acquired resistance in plants. We demonstrated that SA can interfere with group behavior and virulence of the soft-rot plant pathogen Pectobacterium spp. through quorum sensing (QS) inhibition. QS is a population density-dependent communication system that relies on the signal molecule acyl-homoserine lactone (AHL) to synchronize infection. P. parmentieri mutants, lacking the QS AHL synthase (expI-) or the response regulator (expR-), were used to determine how SA inhibits QS. ExpI was expressed in DH5α, the QS negative strain of Escherichia coli, revealing direct interference of SA with AHL synthesis. Docking simulations showed SA is a potential ExpI ligand. This hypothesis was further confirmed by direct binding of SA to purified ExpI, shown by isothermal titration calorimetry and microscale thermophoresis. Computational alanine scanning was employed to design a mutant ExpI with predicted weaker binding affinity to SA. The mutant was constructed and displayed lower affinity to the ligand in the binding assay, and its physiological inhibition by SA was reduced. Taken together, these data support a likely mode of action and a role for SA as potent inhibitor of AHL synthase and QS.

Expression of Hexokinase in Stomata of Citrus Fruit Reduces Fruit Transpiration and Affects Seed Development.

The temporal formation and spatial distribution of stomata on the surface of citrus floral organs and, specifically, on the ovule from which the fruit develops, were analyzed using citrus plants that express green fluorescent protein (GFP) under the guard cell-specific KST1 promoter. Stomata are found on the style, sepal, and anther of the closed flower and on ovules from the stage of anthesis. It has previously been shown that hexokinase (HXK) mediates sugar-sensing in leaf guard cells and stimulates stomatal closure. The activity and response of citrus fruit stomata to sugar-sensing by HXK was examined using plants that express HXK under the KST1 promoter. Those plants are referred to as GCHXK plants. The transpiration of young green GCHXK citrus fruits was significantly reduced, indicating that their stomata respond to sugar similar to leaf stomata. Toward fruit maturation, fruit stomata are plugged and stop functioning, which explains why WT and GCHXK mature yellow fruits exhibited similar water loss. Seeds of the GCHXK plants were smaller and germinated more slowly than the WT seeds. We suggest that the stomata of young green citrus fruits, but not mature yellow fruits, respond to sugar levels via HXK and that fruit stomata are important for proper seed development.

New grapefruit cultivars exhibit low cytochrome P4503A4-Inhibition activity.

Furanocoumarins are the main compounds responsible for the food-drug interactions known as the grapefruit effect, which is caused by the inhibition of CYP3A4-mediated drug metabolism. We evaluated the effects of two new, low-furanocoumarin grapefruit cultivars on CYP3A4 activity and the roles of different furanocoumarins, individually and together with other juice compounds, in the inhibition of CYP3A4 by grapefruit. Whereas a standard grapefruit cultivar inhibited CYP3A4 activity in a dose-dependent manner, neither of the two examined low-furanocoumarin cultivars had an inhibitory effect. Despite the fact that bergamottin and 6',7'-dihydroxybergamottin are weak inhibitors of CYP3A4, their relatively high levels in grapefruit make them the leading cause of the grapefruit effect. We found that furanocoumarins together with other juice compounds inhibit CYP3A4 in an additive manner. In silico docking simulation was employed, and differentiated between high- and low-potency inhibitors, suggesting that modeling may be useful for identifying potentially harmful food-drug interactions.

Impact of scion/rootstock reciprocal effects on metabolomics of fruit juice and phloem sap in grafted Citrus reticulata.

BACKGROUND: Rootstock has a significant impact on plant growth and development, including fruit maturation. However, the existence of mutual interaction between scion and rootstock is often neglected. To explore the origin of different fruit quality traits in citrus, we studied the effect of rootstock and the reciprocal interaction between scion and rootstock of nine combinations; three mandarin varieties grafted on three different rootstocks. We analyzed the metabolic profile of juice via gas and liquid chromatography-mass spectrometry (GC-MS and LC-MS, respectively). Additionally, we profiled phloem sap composition in the scion and the rootstock. Quality traits of fruit and their physio-chemical characteristics were also evaluated. RESULTS: For all three cultivars, rootstock was found to affect fruit yield and biochemical fruit quality parameters (sugar and acidity) in interactions with the scions. In mandarin juice, eight of 48 compounds (two primary and six secondary) were related directly to the rootstock, and another seven (one primary and six secondary) were interactively affected by scion and rootstock. In scion and rootstock sap, six and 14 of 53 and 55 primary metabolites, respectively, were directly affected by the rootstock, while 42 and 33 were affected by rootstock interactively with scion, respectively. CONCLUSION: In this work, we show for the first time a reciprocal effect between rootstock and scion. Based on our results, the scion and rootstock interaction might be organ, distance or time dependent.

Biochemical and Molecular Factors Governing Peel-Color Development in 'Ora' and 'Shani' Mandarins.

To identify factors governing peel-color development in mandarins, we examined carotenoid content and composition and the expression of carotenoid-related genes during four stages of ripening (i.e., green, breaker, yellow, and orange) in two varieties: 'Ora', which has orange fruit, and 'Shani', which has orange-reddish fruit. The two varieties had different carotenoid compositions, and 'Shani' had a significantly higher level of total carotenoid pigments. 'Shani' was rich in the deep orange ß-cryptoxanthin and the orange-reddish ß-citraurin, whereas 'Ora' was rich in the orange violaxanthin. RNA-Seq analysis revealed significantly greater expression of the carotenoid-biosynthesis genes PSY, ßLCY, ßCHX, and CCD4b, as well as MEP-pathway genes and several ethylene-biosynthesis and -signaling genes in 'Shani' fruit. In contrast, the expression levels of genes involved in the synthesis of α-branch carotenoids (i.e., εLCY and εCHX) and ZEP, which is involved in the formation of violaxanthin, were significantly higher in the 'Ora' fruit.

Expression of Arabidopsis Hexokinase in Tobacco Guard Cells Increases Water-Use Efficiency and Confers Tolerance to Drought and Salt Stress.

Abiotic stresses such as drought and saline water impose major limitations on plant growth. Modulation of stomatal behavior may help plants cope with such stresses by reducing both water loss and salt uptake. Hexokinase (HXK) is a sugar-phosphorylating enzyme involved in guard cells' sugar-sensing, mediating stomatal closure and coordinating photosynthesis with transpiration. We generated transgenic tobacco lines expressing the Arabidopsis hexokinase1 (AtHXK1) under the guard cell-specific promoter KST1 and examined those plants using growth room and greenhouse experiments. The expression of AtHXK1 in tobacco guard cells reduced stomatal conductance and transpiration by about 25% with no negative effects on photosynthesis or growth, leading to increased water-use efficiency. In addition, these plants exhibited tolerance to drought and salt stress due to their lower transpiration rate, indicating that improved stomatal function has the potential to improve plant performance under stress conditions.

Mandarin fruit quality: a review.

During the last decade, there has been a continuous rise in consumption and global marketing of fresh, easy-to-peel mandarins, with current annual production of nearly 29 million tons. Nevertheless, most of the existing knowledge on quality traits of citrus fruit comes from research conducted on oranges and grapefruit, which are the main products for the citrus juice manufacturing industry; relatively little is yet known regarding the unique fruit quality traits of mandarins, nor about the great diversity in these traits among the various natural sub-groups and varieties of mandarins. In the present review we discuss the physiological, biochemical, and molecular factors governing key fruit quality attributes of mandarins, including fruit colour, size and shape, ease of peeling, seedlessness, flavour, and nutritional quality. Fruit colour, size, and shape contribute to external appearance; peelability and seedlessness to ease of consumption; and flavour and nutritional quality to internal quality. © 2017 Society of Chemical Industry.

The Solanum tuberosum KST1 partial promoter as a tool for guard cell expression in multiple plant species.

To date, guard cell promoters have been examined in only a few species, primarily annual dicots. A partial segment of the potato (Solanum tuberosum) KST1 promoter (KST1 partial promoter, KST1ppro) has previously been shown to confer guard cell expression in potato, tomato (Solanum lycopersicum), citrus [Troyer citrange (C. sinensis×Poncirus trifoliata)], and Arabidopsis (Arabidopsis thaliana). Here, we describe an extensive analysis of the expression pattern of KST1ppro in eight (previously reported, as well as new) species from five different angiosperm families, including the Solanaceae and the Cucurbitaceae, Arabidopsis, the monocot barley (Hordeum vulgare), and two perennial species: grapevine (Vitis vinifera) and citrus. Using confocal imaging and three-dimensional movies, we demonstrate that KST1ppro drives guard cell expression in all of these species, making it the first dicot-originated guard cell promoter shown to be active in a monocot and the first promoter reported to confer guard cell expression in barley and cucumber (Cucumis sativus). The results presented here indicate that KST1ppro can be used to drive constitutive guard cell expression in monocots and dicots and in both annual and perennial plants. In addition, we show that the KST1ppro is active in guard cells shortly after the symmetric division of the guard mother cell and generates stable expression in mature guard cells. This allows us to follow the spatial and temporal distribution of stomata in cotyledons and true leaves.

Expression levels of antimicrobial peptide tachyplesin I in transgenic Ornithogalum lines affect the resistance to Pectobacterium infection.

The genus Ornithogalum includes several ornamental species that suffer substantial losses from bacterial soft rot caused by Pectobacteria. The absence of effective control measures for use against soft rot bacteria led to the initiation of a project in which a small antimicrobial peptide from an Asian horseshoe crab, tachyplesin (tpnI), was introduced into two commercial cultivars: O. dubium and O. thyrsoides. Disease severity and bacterial colonization were examined in transgenic lines expressing this peptide. Disease resistance was evaluated in six lines of each species by measuring bacterial proliferation in the plant tissue. Three transgenic lines of each species were subjected to further analysis in which the expression level of the transgene was evaluated using RT-PCR and qRT-PCR. The development of disease symptoms and bacterial colonization of the plant tissue were also examined using GFP-expressing strain of P. carotovorum subsp. brasiliense Pcb3. Confocal-microscopy imaging revealed significantly reduced quantities of bacterial cells in the transgenic plant lines that had been challenged with the bacterium. The results clearly demonstrate that tpnI expression reduces bacterial proliferation, colonization and disease symptom (reduced by 95-100%) in the transgenic plant tissues. The quantity of tpnI transcripts, as measured by qRT-PCR, was negatively correlated with the protection afforded to the plants, as measured by the reduced severity of disease symptoms in the tissue.

Diversity among mandarin varieties and natural sub-groups in aroma volatiles compositions.

BACKGROUND: Mandarins constitute a large, diverse and important group within the Citrus family. Here, we analysed the aroma volatiles compositions of 13 mandarin varieties belonging to seven genetically different natural sub-groups that included common mandarin (C. reticulata Blanco), clementine (C. clementina Hort. ex. Tan), satsuma (C. unshiu Marcovitch), Mediterranean mandarin (C. deliciosa Tenore), King mandarin (C. nobilis Loureiro), and mandarin hybrids, such as tangor (C. reticulata × C. sinensis) and tangelo (C. reticulata × C. paradisi). RESULTS: We found that mandarin varieties among tangors ('Temple', 'Ortanique'), tangelos ('Orlando', 'Minneola') and King ('King') had more volatiles, at higher levels, and were richer in sesquiterpene and ester volatiles, than other varieties belonging to the sub-groups common mandarin ('Ora', 'Ponkan'), clementine ('Oroval', 'Caffin'), satsuma ('Okitsu', 'Owari') and Mediterranean mandarin ('Avana', 'Yusuf Efendi'). Hierarchical clustering and principal component analysis accurately differentiated between mandarin varieties and natural sub-groups according to their aroma-volatile profiles. CONCLUSIONS: Although we found wide differences in aroma-volatiles compositions among varieties belonging to different natural sub-groups, we detected only minor differences among varieties within any natural sub-group. These findings suggest that selecting appropriate parents would enable manipulation of aroma-volatile compositions in future mandarin breeding programmes.

Diversity in sensory quality and determining factors influencing mandarin flavor liking.

We evaluated the sensory quality of 42 mandarin varieties that belong to 7 different natural subgroups: common mandarin (Citrus reticulata Blanco), Clementine (Citrus clementina Hort. ex. Tan), Satsuma (Citrus unshiu Marcovitch), Mediterranean mandarin (Citrus deliciosa Tenore), King mandarin (Citrus nobilis Loureiro), and mandarin hybrids, such as tangor (Citrus reticulata × Citrus sinensis) and tangelo (Citrus reticulata × Citrus paradisi). Consumer flavor acceptance tests revealed wide diversity in flavor preferences among mandarin varieties and subgroups. Furthermore, descriptive flavor-analysis tests conducted with the aid of a trained sensory panel revealed that the 9 most preferred varieties had similar flavor profiles, characterized by high sweetness, moderate to low acidity levels, low bitterness and gumminess, strong fruity and mandarin flavor, and high juiciness. The average total soluble solids (TSS) and acidity levels among the highly preferred varieties were 13.1% and 1.1%, respectively. In contrast, the 8 least preferred varieties were either too sour or gummy or had low levels of sweetness, fruity, or mandarin flavor, and either high acidity levels (>1.4%) or low TSS levels (<12.0%). Pearson tests revealed significant positive correlations between flavor acceptance and perceptions of sweetness, fruitiness, and mandarin flavor, and negative correlations with acidity levels and perceptions of sourness, bitterness, and gumminess. Principle component analysis clearly distinguished between highly accepted varieties that were tightly correlated with high TSS levels and perceptions of sweetness fruitiness and mandarin flavor, as compared with the least accepted varieties that were correlated with high acidity levels and perceptions of sourness, bitterness, and gumminess.

Expression of Arabidopsis Hexokinase in Citrus Guard Cells Controls Stomatal Aperture and Reduces Transpiration.

Hexokinase (HXK) is a sugar-phosphorylating enzyme involved in sugar-sensing. It has recently been shown that HXK in guard cells mediates stomatal closure and coordinates photosynthesis with transpiration in the annual species tomato and Arabidopsis. To examine the role of HXK in the control of the stomatal movement of perennial plants, we generated citrus plants that express Arabidopsis HXK1 (AtHXK1) under KST1, a guard cell-specific promoter. The expression of KST1 in the guard cells of citrus plants has been verified using GFP as a reporter gene. The expression of AtHXK1 in the guard cells of citrus reduced stomatal conductance and transpiration with no negative effect on the rate of photosynthesis, leading to increased water-use efficiency. The effects of light intensity and humidity on stomatal behavior were examined in rooted leaves of the citrus plants. The optimal intensity of photosynthetically active radiation and lower humidity enhanced stomatal closure of AtHXK1-expressing leaves, supporting the role of sugar in the regulation of citrus stomata. These results suggest that HXK coordinates photosynthesis and transpiration and stimulates stomatal closure not only in annual species, but also in perennial species.

Genetic diversity among mandarins in fruit-quality traits.

A detailed phenotypic analysis of fruit-quality traits was conducted among 46 mandarin varieties within the Israeli Citrus breeding collection, belonging to genetically different natural subgroups, including common mandarin (C. reticulata Blanco), clementine (C. clementina Hort. ex. Tan), satsuma (C. unshiu Marcovitch), Mediterranean mandarin (C. deliciosa Tenore), King mandarin (C. nobilis Loureiro), and mandarin hybrids, such as tangor (C. reticulata × C. sinensis) and tangelo (C. reticulata × C. paradisi). Evaluated qualities included physical attributes (size, shape, color, peel thickness, and seed number); physiological properties (ripening period, peelability, and segmentation); nutritional and biochemical composition (vitamin C, phenol, flavonoid, and carotenoid contents and total antioxidant activity); and sensory attributes (total soluble solids and acid levels, flavor preference, sweetness, sourness, and fruitiness). The results indicated wide genetic variability in fruit-quality traits among mandarin varieties and natural subgroups, and statistical and hierarchical clustering analysis revealed multiple correlations among attributes. Such phenomic analysis is an obligatory requirement for identification of molecular markers for distinct fruit-quality traits and for selection of appropriate parents for future breeding programs.