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Biostimulants have become highly important in agriculture. For these products to be efficient, they need to be formulated, for a specific crop, according to the mineral nutrients and metabolites requirements in each phenological phase of the crops. In this study, the agronomical behavior of 10 tomato varieties was evaluated (‘Cherry’, ‘Corazón de Buey’, ‘Green Zebra’, ‘Marglobe’, ‘Marmande VR’, ‘Montserrat’, ‘Muchamiel’, ‘Óptima’, ‘Roma VF’ and ‘Tres Cantos’), in other to select four varieties with the greatest agronomical differences between them to be analyzed by omics tools. So, the varieties ‘Cherry’, ‘Green Zebra’, ‘Montserrat’, and ‘Tres Cantos’ were selected for an ionomic, metabolic, and hormone study to determine the predominant nutrients and metabolites in the different phenological phases, and to relate it with its agronomic characteristics. It was observed that the variability of the results could be mainly explained by the different phenological phases during the development of the crop, rather than by the variety. The major compounds were N (4.71 g 100 g dw), K (3.86 g 100 g dw), P (0.53 mg g dw), glutamate (5.21 mg g dw), glutamine (2.89 mg g dw), aspartate (1.54 mg g dw), tyrosine (2.36 mg g dw), phenylalanine (1.70 mg g dw), sucrose (14.4 mg g dw), malate (13.2 mg g dw), and isopentenyladenine (iP) (2.65 ng g dw). No correlation was found between any specific compound and an agronomic characteristic. But, it can be concluded that Biostimulant products must contain these compounds in other to stimulate growth and increase the production of tomatoes plants, as they comprise most of the metabolites and nutrients needed in some or all of the phenological phases., Acknowledgments This research was funded by State R&D Program Oriented to the Challenges of the Society, Innovation and Science Ministerial (Spain Government), grant number RTC-2016–4568–2. We acknowledge the support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

In order to understand photosynthetic responses of pomegranate plants (Punica granatum L.) to salinity, an experiment was conducted with three varieties, 'Mollar de Elche', 'Valenciana', and 'Wonderful', irrigated with seven salt concentrations (0, 40, 60, 80, 100, 120, and 140 mM NaCl). At the end of the experiment, parameters of gas exchange, chlorophyll fluorescence, water relations, and sugar and chloride concentrations were measured in leaves. As the concentration of NaCl increased, the concentration of Cl- in leaves was elevated, and the CO2 assimilation rate, stomatal conductance, variable fluorescence/maximum fluorescence ratio, PSII quantum yield, and total soluble sugars decreased. In 'Valenciana', the decrease of the net assimilation of CO2 could occur due to the closure of stomata, while in 'Mollar' and 'Wonderful', this was due to damage caused by Cl- toxicity. The study of carbohydrates also suggests a different behavior of carbon metabolism in the three varieties.

This study explores the possibility of using mycorrhization as a novel technique for diminishing the negative effects of boron (B) in the nutrient solution on seedlings of Carrizo citrange rootstock plants. For this, an experiment was planned for studying the physiological (gas exchange and chlorophyll fluorescence parameters), morphological (vegetative growth parameters), nutritional (organic solutes, carbohydrates) and oxidative stress responses of seedlings that were either mycorrhized (+AM, Rhizophagus irregularis; previously known as Glomus intraradices) or not mycorrhized (-AM), and irrigated with water containing different concentrations of B (0.5, 5 and 10 mg L−1). It was observed that an excess of B in the nutrient solution decreased the vegetative growth in both +AM and -AM plants, but this decrease was greater in -AM plants. Mycorrhized plants (+AM) under high B concentration accumulated less B in the leaves, and had a smaller reduction of net assimilation rate of CO2 and lower MDA concentration than non-mycorrhized plants. Thus, it can be concluded that mycorrhization increased the tolerance to high boron concentration in the irrigation water of citrange Carrizo seedlings by reducing both the B concentration in the plant tissue and the B toxicity in the physiological processes. The study of organic solutes and carbohydrates also pointed to a different response model between +AM and -AM plants that could be related to the different tolerance observed between these plants.

Rootstocks are a vital element of commercial citrus production. A varied level of salinity tolerance has been described for citrus rootstock cultivars, however, the effects of the rootstock can be scion-dependent. Our objective was to determine if rootstock selection has an influence on the salt-tolerance of 2-year-old Kinnow mandarin plants grafted onto two salt-sensitive (Carrizo citrange and Sanchton citrumello) and two salt-tolerant (Rangpur lime and Rubidoux) rootstock cultivars. Kinnow mandarin scion was grafted on these four rootstocks and irrigated with water containing 0, 30, 60, 90, or 120 mM NaCl. At the end of the experiment (90 days of salinization) growth, leaf gas exchange and chlorophyll fluorescence parameters, leaf and root Cl and Na concentrations, and parameters related to the antioxidant system were measured. Under salinity stress, plants grafted on salt-tolerant rootstocks had less reduction in plant biomass, total chlorophyll content, photosynthesis rate, stomatal conductance, and internal CO2 concentration as compared to the plants grafted on salt-sensitive rootstocks. Similarly, plants with salt-tolerant rootstocks had lower reactive oxygen species, suggesting enhanced activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase), and higher accumulation of osmolytes (proline and glycinebetaine). In addition, for plants with salt-tolerant rootstocks the levels of Na and Cl were higher in roots while lower in leaves; the opposite was the case for plants grafted on salt-sensitive rootstocks. Therefore, the selection of the rootstock can enhance the salt-tolerance potential by enhancing antioxidant activities, increasing concentrations of osmoprotectants, and limiting leaf levels of Na and Cl. Kinnow mandarin plants grafted on Rangpur lime or Rubidoux showed more salt tolerance than those on Carrizo citrange or Sanchton citrumello.

Cadmium is absorbed by plants rapidly and without control through the same channels as other essential metals, interfering with their transport and utilization. Many studies have shown that selenium could be utilized as a way to avoid this unwanted transport and other negative effects of Cd. For this reason, the present research study was conducted with four treatments (−Cd/−Se, +Cd/−Se, +Cd/+SeF, and +Cd/+SeR) to determine the type of application of Se that is best (foliarly and/or via the root) as regards the reduction of the toxic effects of Cd on plants. Our results showed that the Cd excess in the nutrient solution resulted in a decrease in the total dry biomass of the plants grown under these conditions, and this decrease was due to the reduction of the growth of the shoot (48% +Cd/−Se, 45% +Cd/+SeF, and 38% +Cd/+SeR, relative to −Cd/−Se). This reduction in growth was due to: (i) the toxicity of Cd itself and (ii) the nutritional disequilibrium suffered by the plants. It seems that under hydroponic conditions, the addition of Se to the nutrient solution, and therefore its absorption through the roots (lower antioxidant activity, superoxide dismutase, H2O2 concentration and higher catalase activity), greatly delayed and reduced the toxic effects of Cd on the pepper plants, as opposed to the foliar application of this element.

Background: Presently, irrigation waters often have a high concentration of boron (B), and the fruit trees in the Mediterranean areas, in general, are exposed to a high risk of B toxicity. Aims: To test the hypothesis that pomegranate trees are very tolerant to the presence of B in the irrigation water, to elucidate the physiological mechanisms behind this tolerance, and to assess differences between different varieties. Methods: In this study, the physiological and nutritional behavior of three pomegranate cultivars (‘Mollar de Elche', ‘Valenciana', and ‘Wonderful'), treated with five B concentrations (0.25, 1.25, 2.5, 5.0, 10.0 mg L), were studied. At day 30 and 60 after the start of the treatments, growth measurements, gas exchange parameters and organic solutes were recorded. Results: Almost no significant differences were observed between the B treatments for any of the cultivars. Increasing the B concentration in the nutrient solution increased B concentrations in the leaves, but they never exceed 40 mg kg of B. In the roots, however, B concentrations were very high, up to 400 mg kg. Conclusion: Pomegranate trees are very tolerant to B excess due to their ability to accumulate B in great quantities in the root, without causing toxicity to this part of the plant, thus limiting its transport to the shoots., The authors are grateful to the Project on Genetic Resources, Preservation of Endangered Species: pomegranate and quince. Ref. RFP2012-00009-00-00, funded by INIAMINECO and FEDER for the maintenance of pomegranate tree and quince collection with which this study was performed

© 2020 by the authors., Tomato (Solanum lycopersicum L.) is one of the most important crops worldwide as per its production and the surface cultivated. The use of biostimulant products plays a fundamental role in mitigating the negative effects of climate change and reducing the use of conventional fertilizers. Many of these products are formulated with amino acids (AAs). This study was conducted to elucidate the effects of the foliar application of tyrosine (Tyr) (15 mM), lysine (Lys) (15 mM), methionine (Met) (15 mM), and a Tyr + Lys + Met (15 mM + 15 mM + 15 mM) mixture on the physiological and metabolic processes, vegetative growth, and nutritional state of Optima variety tomato plants. The results showed that application of the AAs, individually and combined, was beneficial for the growth of the aerial part, net assimilation of CO2, and water use efficiency (WUE). Application of Tyr resulted in the best WUE. The metabolomics study revealed that AA treatments increased the concentration of proline, fructose, and glucose, whose role was to stimulate glycolysis and the Krebs cycle. Thus, the plants could have greater reduction power and energy, as well as more carbon molecules for their growth processes., This research was funded by the State R&D Program Oriented to the Challenges of the Society, Innovation, and Ministerial Science (Spain government), grant number RTC-2016-4568-2.

Citrus rootstocks, (i.e. Carrizo citrange, Cleopatra mandarin, and Forner-Alcaide no5) influence the agronomical and physiological behavior of citrus trees under unfavorable environmental conditions. Citrus are very sensitive to boron (B) toxicity. However, when good-quality water is scarce, growers must use water treatment and desalination plant water for irrigation, which may have a B concentration that is above the threshold recommended for citrus trees (0.5 mg L−1). There is little information on the relative tolerance of citrus rootstocks to an excess of B, and the physiological and biochemical mechanisms involved. In this work, the morphological, physiological, biochemical and nutritional responses of three citrus rootstock plants, Carrizo citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and Forner-Alcaide no 5 (Cleopatra mandarin × Poncirus trifoliata (L.) Raf.), under different concentrations of B in the irrigation water (0.25, 5 and 10 mg L−1), grown in containers in a greenhouse, were studied. The results showed that Carrizo citrange was very sensitive to B toxicity, as the plants had the most reduced vegetative growth, the greatest concentration of B in their leaves, stem and roots, a greater concentration of malondialdehyde in leaves, and a lesser net assimilation of CO2. The other two genotypes did not show differences in the accumulation of B in their tissues. Nevertheless, Cleopatra mandarin showed a greater tolerance, as its photosynthetic system was less affected by B toxicity, probably due to its potent antioxidant system, which is based on a high activity of catalase, which restricts the accumulation of malondialdehyde in its leaves. Forner-Alcaide no 5 had an intermediate tolerance, similar to Cleopatra mandarin than to Carrizo citrange, as per the accumulation of B in its leaves. Forner-Alcaide no 5 was the only genotype whose root was not affected by B toxicity.

In the present work, the coordinates L*, a* and b* from the CIELAB color space, as well as the chlorophyll, total carotenoids and the content of the carotenoids Lutein and β-cryptoxanthin were measured in the skin of fruits from the Fino 49 lemon during its development, with the aim of understanding the relationship that exists between the color changes of the fruit’s skin (color coordinates) and the pigment content. Also, the understanding of the relative importance of the contents of lutein and β-cryptoxanthin with respect to the total content of carotenoids was sought. The period of study lasted three years; from September 2015 to January 2016, from September 2016 to January 2017, and from September 2017 to January 2018, the periods that comprised the color changes of the lemon fruit until its harvest. The fruits were measured every two weeks in the experimental plot of the IMIDA (Murcian Institute of Agricultural and Food Research and Development) located at La Alberca (Murcia, Spain) and in the experimental orchards from the CEBAS-CSIC, located in Santomera (Murcia). During the experiment, the color and chlorophyll, Lutein and β-cryptoxanthin concentrations were measured. The results showed that there was a good correlation between the color coordinates and the pigments responsible for the lemon’s skin color: all the color pigments were correlated with the a*, b* color coordinates and the Hue angle index. Throughout the fruit’s maturation, a degradation of the chlorophylls was observed, as well as an increase of β-cryptoxanthin, which is responsible for the green and yellow color of the fruits, respectively. Lutein, which was found in high concentrations, decreased with time, but did not contribute to the fruit’s color.

In citrus, the effects of an excess of boron (B) are conditioned by the type of rootstock. In the present work, the morphological, physiological and biochemical responses of seedlings from three citrus genotypes, commonly used as rootstocks in citriculture. In particular, Citrange Carrizo (CC), Citrus macrophylla (CM) and sour orange (SO) seedlings were treated with an excess of B (10 mg L-1) in the nutrient solution in order to determine the relative tolerance and to understand the possible mechanisms that make a rootstock more tolerant than the others. To assess these responses, different parameters were measured in plants, such as vegetative growth, B concentration in leaves, stems and roots, gas exchange and chlorophyll fluorescence, the concentration of osmolytes and the activity of enzymes related to the antioxidant system. The results showed, according to the growth parameters, that the SO rootstock was the most tolerant to an excess of B; while CC was the most sensitive. This result was due to the fact that SO plants accumulated less B in leaves, as its roots have a great capacity of restricting the uptake and transport of B towards the aerial part. Moreover, SO is suggested to diminish B toxicity risk through its antioxidant system, since it presented high activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), as well as high accumulation of quaternary ammonium compounds (QACs).

Pomegranate ( Punica granatum L.) is known for its great resistance to abiotic stresses such as salinity or drought. However, its behavior under flooding − which is very common in the southeast of Spain, due mainly to the presence of heavy soils − has not yet been studied. This experiment was carried out in a greenhouse, with three of the pomegranate varieties most used in southeastern Spain: ‘Mollar de Elche’, ‘Valenciana’, and ‘Wonderful’. The plants were immersed in containers of 20 liters capacity, leaving the water level three centimeters above the root zone for six days. Measurements of growth parameters, water relations, gaseous exchange parameters, chlorophyll fluorescence, organic solutes, oxidative stress, and the hormonal response were performed. The first variety that showed symptoms of stress was ‘Valenciana’, the one whose water relations, gaseous exchange parameters, total dry biomass, and chlorophyll fluorescence were affected most. It was also the one with the worst hormonal response. The flooding also negatively affected the growth parameters of ‘Wonderful’ and ‘Mollar de Elche’, but much less than in ‘Valenciana’. From this study we can conclude that flooding tolerance of pomegranate crops depend on the cultivar. So, 'Valenciana' cultivar was the most sensitive and 'Mollar de Elche' the most tolerant.

Boron (B), an essential nutrient for plants, participates in many physiological processes, with emphasis its role in the formation of the plant's cell wall. In soil, the range between deficiency and toxicity of B is very narrow as compared to other nutrients, which makes its management in agriculture very difficult, as it depends on the soil and environmental conditions. B stress simultaneously acts with others (extreme temperatures, excess of light, high concentration of CO2, drought, salinity or heavy metal contamination, etc.). The effects of these other stresses could increase the sensitivity of plants to B toxicity or deficiency. The simultaneous combination (B stress × other abiotic stresses) is a complex interaction that should be analyzed in detail if the resistance of crops to climate change is needed. This article reviews the response of plants when facing a combination of B stress with other stresses, and compares this response with the individual stresses. Also, in the last few years, the role of B has been described in multiple plant functions that can improve its resilience to specific stresses. Thus, this article also analyses in what conditions the application of B can be efficient for the improvement of the plant's response to other stresses.

The external color of lemons is one of the most important attributes for the consumer. It is known that the natural process of de-greening mainly depends on the temperature, although other agronomic factors could also affect this process. Currently, citrus orchards in Eastern Spain suffer drought and salinity problems, and growers use a series of agronomic strategies − such as the use of tolerant rootstocks, shade screens, or mulching − to mitigate them. However, the effects of all these factors on the fruit color are unknown. “Fino 49” lemon trees were used to study the effects of the rootstock, shade screens, and mulching on the color of lemon fruits in two individual trials. In one trial, trees grafted on Citrus macrophylla (salt sensitive rootstock) were irrigated with water of different salinity levels (CE: 0.8, 3.8, and 6.8 dS/m) and, in the second trial, trees grafted on Sour orange (a drought sensitive rootstock) were watered under different watering regimes (100% ETc, 60% ETc, and 40% ETc). Measurements of the a*, b*, and L* coordinates during the development of the fruit in two consecutive growing seasons were taken. Also, the water potential and the concentration of chloride were measured in the leaves. The results show that the start of color change was only dependent on the minimum average temperature in a period of 14 days, regardless of the rootstock. However, the final fruit color was altered by some of the factors assayed. The use of shade screens produced fruits that were less yellow than those subjected to mulching or grown in open field. For the trees under the shade screens, the drought treatments also negatively affected the de-greening process, as greenish fruits were produced. In contrast, trees grown in the open and watered with salt-treated water produced fruits that were more yellow than the fruits grown normally. The results indicate that excess solar radiation or a severe decrease in the leaf water potential diminished fruit coloration, while a high concentration of foliar Cl- accelerated the de-greening process.

Salinity is one of the most critical problems faced by agriculture in all the arid and semi-arid climates in the world. Many biostimulant-producing companies utilize different raw materials to palliate the negative effects of salinity on crops. Some of these active materials are amino acids (AAs). In this study, the effect of the foliar application of free amino acids or as a mixture of them was studied in tomato plants cv “Optima”, grown in a controlled environment growth chamber in a hydroponic system with Hoagland’s solution with added 50 mM NaCl. The following treatments were applied: i) Control (-salt), ii) salt (+salt), and the salt treatments with amino acids (AAs + salt): iv) L-Arg, v) L-Pro, vi) Glu, vii) L-Trp, viii) L-Met + L-Arg, ix) L-Met + L-Trp, x) Glu + L-Pro. At the end of the assay, vegetative growth parameters, relative water content, mineral nutrient content, carbohydrates and organic solutes and chlorophylls were measured. The results showed that salinity decreased the growth of the plants, but those treated with the L-Met, Pro + Glu and Met + Trp reversed the negative effect of salinity. Also, this result was not due to differences in the concentration of Cl- or Na+ in the leaves, or to changes in the water status of the plants, but to a greater accumulation of total soluble sugars induced by the application of AAs, which could have de-activated the reactive oxygen species created by the toxicity of these ions. The results of this experiment also highlight the antagonistic or synergistic effects between the AAs, which should be taken into account by fertilizer producers.

Background The current need to produce food for a growing population, from diminishing natural resources, such as water and energy, and with minimum environmental degradation, demands the optimization of production. We compare the economic feasibility of tomato production in an open system with a perlite substrate, a closed system with the nutrient film technique (NFT), and a hydroponic crop (deep flow technique, DFT) using three levels of salinity that are found within the normal range for irrigation water quality in southeastern Spain. Results Production with DFT resulted in an increase in the cost of phytosanitary treatments and the cost of maintenance. Production with perlite resulted in an increase in the cost of irrigation water and fertilization, and the use of NFT resulted in an increase in energy costs. The point of price equilibrium was exceeded in the three soilless systems when using low salinity water, and in perlite, with intermediate salinity water. Conclusion Profitability was reduced in the following order: perlite > NFT > DFT. There were positive results when using irrigation water with low salinity, and in the case of perlite, with intermediate salinity. In every case, salinity reduced the profitability of the operation, and this was greater when NFT was employed. The analysis of these soilless systems should be continued to determine the possibility of reducing cultivation costs. © 2019 Society of Chemical Industry.

Spain is the second-largest lemon fruit producing country in the world. Approximately 80% of the lemon production occurs in the arid southeast (Murcia and Alicante) region of Spain. For citrus fruits, 50% shade screen reduces the leaf temperature and light intensity at midday in the summer and the spring in these areas, resulting in an increase in the photosynthetic leaf water-use efficiency (WUEphy = A/Eleaf). In this experiment, the effect of shading with Aluminet-50 screen (which reduces approximately 50% of the incident photosynthetically active radiation) on agronomical responses of ‘Fino 49’ lemon trees (Citrus limon (L.) Burm. fil.) grafted on two rootstocks, Citrus macrophylla and Citrus aurantium L., were studied. This study was conducted in Santomera (Murcia) over a 4-year period (2008–2011) on 7-year-old lemon trees. Shade screen increased the height, canopy perimeter and canopy volume compared to those under full sunlight. However, shading effect reduced fruit production. Trees under full sunlight produced a total of 81 and 45 kg/tree, while trees under shade produced 70 and 33 kg/tree of C. macrophylla and C. aurantium L., respectively. Shading affected the physical characteristics of C. macrophylla fruits because fruits from trees under shade had lesser fresh weight and smaller width compared to those under full sunlight.

Scarcity of water is a severe limitation in citrus tree productivity. There are few studies that consider how to manage nitrogen (N) nutrition in crops suffering water deficit. A pot experiment under controlled-environment chambers was conducted to explore if additional N supply via foliar application could improve the drought tolerance of Citrus macrophylla L. seedlings under dry conditions. Two-month-old seedlings were subjected to a completely random design with two water treatments (drought stress and 100% water/field capacity). Plants under drought stress (DS) received three different N supplies via foliar application (DS: 0, DS + NH4NO3: 2% NH4NO3, DS + KNO3: 2% KNO3). KNO3-spraying increased leaf and stem DW as compared with DS + NH4NO3 and DS treatments. Leaf water potential (Ψw) was decreased by drought stress in all the treatments. However, in plants from DS + NH4NO and DS + KNO3, this was due to a decrease in the leaf osmotic potential, whereas the decrease in those from the DS treatment was due to a decrease in the leaf turgor potential. These responses were correlated with the leaf proline and K concentrations. DS + KNO3-treated plants had a higher leaf proline and K concentration than DS-treated plants. In terms of leaf gas exchange parameters, it was observed that net assimilation of CO2 [Formula: see text] was decreased by drought stress, but this reduction was much lower in DS + KNO3-treated plants. Thus, when all results are taken into account, it can be concluded that a 2% foliar-KNO3 application can enhance the tolerance of citrus plants to water stress by increasing the osmotic adjustment process.

In this study, we characterized the chemical and physical aspects of eleven commercial mandarins [‘Clementine’ (‘Clementina Fina’, ‘Clemenules’, ‘Hernandina’), tangor (‘Ortanique’, ‘Afourer’, ‘Ellendale’), and hybrid cultivars (‘Fortuna’, ‘Kara’, ‘Mor’, ‘Nova’ and ‘Yosemite’)] in the Spanish southeast. The analysis revealed that ‘Ellendale’ showed the highest amount of juice, ‘Nova’ and ‘Clementina Fina’ displayed high total soluble solids and low titratable acidity, and ‘Clementina Fina’ showed a particularly high concentration of Potassium. The cultivars ‘Clementina Fina’ and ‘Clemenules’ were the mandarins most appropriate for fresh consumption, with small-medium sized fruits and a high percentage of excellent quality juice.

This chapter outlines irrigation and fertilizer management in lime trees (Rutaceae), exploring their water requirements, the different irrigation systems used currently and how these strategies have to be modified according to the different soil, climatic and water resource characteristics. In the fertilizer application section, the role of the different mineral nutrients in the physiological processes of this crop is described. The most commonly used fertilizers are discussed, along with how to reach an optimum nutritional range in the trees, thereby avoiding nutritional imbalance.