Effects of Grafting on Alkali Stress in Tomato Plants: Datura Rootstock Improve Alkalinity Tolerance of Tomato Plants

Plant growth, nutritional status, and proline content were investigated in non-grafted and grafted greenhouse tomato plants onto five rootstocks of eggplant, datura, orange nightshade, local Iranian tobacco, and field tomato, exposed to 0, 5, and 10 mM sodium bicarbonate (NaHCO₃) to determine whether grafting could improve alkalinity tolerance of tomato. The leaf fresh mass of ungrafted and grafted tomato plants decreased significantly as NaHCO₃ levels increased. Despite other rootstocks and ungrafted plants, alkalinity had no significant effect on stem and root fresh mass and shoot phosphorus (P), potassium (K) and magnesium (Mg) concentrations of datura grafted plants. The lowest solution pH and electrical conductivity (EC) values and the highest leaf proline content were observed in the plants grafted onto datura rootstock. Moreover, sodium (Na) concentration in shoots was lower in plants grafted onto datura rootstock than in other plants especially under high NaHCO₃ levels. Overall, using datura rootstock improved alkalinity tolerance of tomato plants under NaHCO₃ stress.     

高温逆境下嫁接番茄耐热特性研究

以赤茄、粘毛茄、北农茄砧和托鲁巴姆为砧木，研究了嫁接番茄对夏季高温的抵御能力，以及对果实品质的影响。结果表明：高温下北农茄砧嫁接番茄叶片游离脯氨酸、蛋白质的含量均较番茄自根苗多，同时POD与APX活性较高，表现出较强的抗热能力；以赤茄为砧木嫁接番茄叶片POD与APX活性较低，叶片游离脯氨酸、蛋白质的含量减少，耐热性降低。嫁接显著地提高了番茄果实有机酸含量，降低了果实蛋白质含量。嫁接对果实维生素C、还原糖含量影响较小。     

Status of photosynthetic pigments,lipid peroxidation and anti-oxidative enzymes in Vigna mungo in presence of arsenic

The response to arsenic was evaluated for photosynthetic pigments, lipid peroxidation and anti-oxidative enzymes in black gram. Black gram (Vigna mungo) subjected to arsenic doses of 100 µM and 200 µM, showed increased amount of lipid peroxidation. Activity of peroxidase (POD) increased tremendously in arsenic treated Vigna leaves over control. Similarly, activities of enzymes like superoxide dismutase (SOD) and ascorbate peroxidase (APX) also increased with increase in arsenic. Analysis of native PAGE superoxide dismutase activity showed one manganese (Mn)-SOD and two copper/zinc (Cu/Zn)-SOD isoenzymes in black gram leaves, whose intensity increased especially at 200 µM arsenic treatment. However, activity of catalase (CAT) decreased with increase in concentrations of arsenic. This clearly indicates that except CAT, all studied antioxidative enzymes like SOD, POD and APX showed increased expression at arsenic treatments, which reflects their protective role against arsenic toxicity in black gram plants. Photosynthetic pigments like chlorophyll and carotenoids showed reduction with increasing concentrations of arsenic in treatment solutions.     

高温逆境下嫁接番茄耐热特性研究

以赤茄、粘毛茄、北农茄砧和托鲁巴姆为砧木,研究了嫁接番茄对夏季高温的抵御能力,以及对果实品质的影响。结果表明:高温下北农茄砧嫁接番茄叶片游离脯氨酸、蛋白质的含量均较番茄自根苗多,同时POD与APX活性较高,表现出较强的抗热能力;以赤茄为砧木嫁接番茄叶片POD与APX活性较低,叶片游离脯氨酸、蛋白质的含量减少,耐热性降低。嫁接显著地提高了番茄果实有机酸含量,降低了果实蛋白质含量。嫁接对果实维生素C、还原糖含量影响较小。     

Effects of three commercial rootstocks on mineral nutrition,fruit yield,and quality of salinized tomato

Tomato (Solanum lycopersicum Mill. cv. Belladona F₁) plants were either self‐rooted, self‐grafted, or grafted onto the commercial rootstocks “Beaufort”, “He‐Man”, and “Resistar” and grown in a recirculating hydroponic system. Three nutrient solutions differing in NaCl‐salinity level (2.5, 5.0, and 7.5 dS m^–1, corresponding to 0.3, 22, and 45 mM NaCl) were combined with the five grafting treatments in a two‐factorial (3 × 5) experimental design. At the control NaCl level (0.3 mM), fruit yield was not influenced by any of the grafting treatments. However, at low (22 mM NaCl) and moderate (45 mM NaCl) salinity levels, the nongrafted and the self‐grafted plants gave significantly lower yields than the plants grafted onto He‐Man. The plants grafted onto the other two rootstocks gave higher yields only in comparison with the nongrafted plants, and the differences were significant only at low (Beaufort) or moderate (Resistar) salinity. Yield differences between grafting treatments at low and moderate salinity arose from differences in fruit number per plant, while mean fruit weight was not influenced by grafting or the rootstock. NaCl salinity had no effect on the yield of plants grafted onto He‐Man but restricted the yield in all other grafting treatments due to reduction of the mean fruit weight. With respect to fruit quality, salinity enhanced the titratable acidity, the total soluble solids, and the ascorbic acid concentrations, while grafting and rootstocks had no effect on any quality characteristics. The leaf Na concentrations were significantly lower in plants grafted onto the three commercial rootstocks, while those of Cl were increased by grafting onto He‐Man but not altered by grafting onto Beaufort or Resistar in comparison with self‐grafted or nongrafted plants. Grafting onto the three tested commercial rootstocks significantly reduced the leaf Mg concentrations, resulting in clear Mg‐deficiency symptoms 19 weeks after planting.     

Tomato and eggplant scions influence the effect of rootstock under Na2SO4 salinity

A short-term experiment was conducted to investigate whether the effect of rootstock on plant response to salinity depends on the solanaceous species used as scion. Tomato cv. ‘Ikram’ and eggplant cv. ‘Black Bell’ were grafted onto two tomato interspecific hybrids (‘Beaufort’ and ‘He-Man’). Plants were grown in an open soilless cultivation system and supplied with two nutrient solutions: non-saline control and a saline solution (adding 15 mM Na₂SO₄, 3.7 dS m^?1). Plant dry biomass production and partitioning were influenced by salinity, but its effect was depending on the rootstock/scion combination. ‘Beaufort’ eliminated the deleterious effect of salinity when tomato was used as scion, but reduced (?29.6%) the shoot biomass of eggplant. ‘He-Man’ had a different effect on scion growth under saline conditions: shoot biomass was less reduced in eggplant (?20.6%) than in tomato (?26.8%). Under salt stress, ‘Beaufort’ reduced the accumulation of Na⁺ in tomato leaves more than in eggplant, whereas no differences were observed between tomato and eggplant grafted onto ‘He-Man’. Stem Na⁺ accumulation followed a different pattern. The increase of Na⁺ in the stems was similar for tomato and eggplant grafted onto ‘Beaufort’, whereas stems of tomato accumulated more Na⁺ compared to eggplant grafted onto ‘He-Man’. The opposite response of the tested rootstocks to salt stress when the scion was either tomato or eggplant seems to be partially related to the capacity of the rootstock and scion to exclude Na⁺ from the shoot. However, the results of nutrient accumulation within plant tissues imply that other mechanisms in addition to ion competition are involved in the salt resistance of grafted plants.     

Bioefficacy of Hen Feather Keratin Hydrolysate and Compost on Vegetable Plant Growth

ABSTRACT

The potential of keratin wastes originating from poultry farms in practical application as a valuable organic fertilizer, gives rise to the need for intensive study on their effect on plants. In this study, for the first time there has been examined the influence of hen feather keratin bio-hydrolysate (FKH) and hen feather keratin compost (FKC) on plant growth, and the following features that indicate the plant condition: the leaf chlorophyll content, the activity of phenylalanine ammonia lyase (PAL) and guaiacol peroxidase (GPX) enzymes. The results of pot experiments showed a potential plant growth promoting effect of FKH, applied as a leaf treatment and of FKC manure. Fertilization of tested plants with FKC resulted in significant increase of their fresh weight. There was no effect on plant biomass after FKH treatment. The stimulating effect on plant physiology was expressed by decreased PAL activity after FKC treatment, and enhanced GPX activity, after FKH and FKC treatment. The application of FKC as a manure gave better effects for the plant condition expressed by the activity of PAL and GPX in comparison with FKH spraying. The chlorophyll content did not prove to be an efficient parameter to evaluate the impact of FKH or FKC on white cabbage, tomato, and maize plant. However, a significant increase in the leaf chlorophyll a, b, and a+b concentration was observed in cucumber plant after FKC treatment. Among the tested plants, the cucumber has shown the most profitable effect of feather compost on plant growth.     

The Effect of Cadmium Toxicity and Silicon Supplementation on the Activity of Antioxidative Enzymes and the Concentration of Zinc and Iron in Hydroponically Grown Cucumber

Two cucumber cultivars (Cucumis sativus L.) exposed to three cadmium (Cd) concentrations (0, 1, and 5 μM) were supplemented or un-supplemented with silicon (Si) (1 mM). Exposure to 1 μM Cd had no effect on shoot and root dry mass, whereas exposure to 5 μM Cd significantly reduced plant growth. Addition of Si stimulated the growth of Cd-treated cucumber. Exposure to 5 μM Cd significantly increased shoot Cd concentration and decreased iron (Fe) and zinc (Zn) concentration. Plants supplied with Si had lower Cd and higher Zn and Fe compared with unsupplied plants. Exposure to Cd resulted in a higher production of malondialdehyde (MDA). Si nutrition partly ameliorated lipid peroxidation induced by Cd toxicity. Activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and catalase (CAT) decreased, whereas ascorbate peroxidase (APX) activity increased in response to 5 μM Cd. Induction of APX activity might play an important role in the response of cucumber to Cd toxicity.     

EFFECT OF DIFFERENT ROOTSTOCKS ON GROWTH,CHLOROPHYLL A FLUORESCENCE AND MINERAL COMPOSITION OF TWO GRAFTED SCIONS OF TOMATO

Two tomato scions (cvs. ‘Raf’ and ‘Gorety’) were grafted on three different rootstocks: S. torvum, ‘Beaufort’ (Lycopersicum esculentum × Lycopersicum hirsutum) and intermediate grafting of eggplant ‘Cristal’ between tomato and S. torvum (double graft). Plants were grown in Mediterranean greenhouse conditions. The response to grafting was measured through growth parameters, F_v/F_m and leaf macronutrients analysis, and it was compared with non-grafted plants. The scions grafted on S. torvum in simple and double graft showed lower fresh and dry weight of leaves, number of commercial fruits, plant height, F_v/F_m and decreased their capacity to absorb several nutrients resulting in a lower mineral concentration in scions leaves, as a result of a thickened graft union. On the other hand, both scions showed a good response when grafted on the rootstock ‘Beaufort’, with which growth parameters, yield and photosynthetic capacity were similar to non-grafted plants.     

Kinetics of Zinc Uptake and Anatomy of Roots and Leaves of Coffee Trees as Affected by Zinc Nutrition

Abstract

The influence of silicon (Si) (2.5 mM), sodium chloride (NaCl) (100 mM), and Si (2.5 mM) + NaCl (97.5 mM) supply on chlorophyll content, chlorophyll fluorescence, the concentration of malondialdehyde (MDA), H₂O₂ level, and activities of superoxide dismutase (SOD; E.C.1.15.1.1.), ascorbate peroxidase (APx; E.C.1.11.1.11.), catalase (CAT; E.C.1.11.1.6.), guaiacol peroxidase (G-POD; E.C.1.11.1.7.) enzymes, and protein content were studied in tomato (Lycopersicon esculentum Mill c.v.) leaves over 10-day and 27-day periods. The results indicated that silicon partially offset the negative impacts of NaCl stress with increased the tolerance of tomato plants to NaCl salinity by raising SOD and CAT activities, chlorophyll content, and photochemical efficiency of PSII. Salt stress decreased SOD and CAT activities and soluble protein content in the leaves. However, addition of silicon to the nutrient solution enhanced SOD and CAT activities and protein content in tomato leaves under salt stress. In contrast, salt stress slightly promoted APx activity and considerably increased H₂O₂ level and MDA concentration and Si addition slightly decreased APx activity and significantly reduced H₂O₂ level and MDA concentration in the leaves of salt-treated plants. G-POD activity was slightly decreased by addition of salt and Si. Enhanced activities of SOD and CAT by Si addition may protect the plant tissues from oxidative damage induced by salt, thus mitigating salt toxicity and improving the growth of tomato plants. These results confirm that the scavenging system forms the primary defense line in protecting oxidative damage under stress in crop plants.     

Avocado rootstock influences scion leaf mineral content

ABSTRACT

To test the influence of avocado rootstocks on the scion leaf ionome, the nutritional status of avocado cultivars Hass and Ettinger grafted onto 15 rootstocks was compared over 3 years. The rootstocks were of different genetic origins (West Indian or Mexican) and were clonally or reproductively propagated. The trees were grown in a high-density orchard, and were continually fertigated as is common in modern avocado orchards. Leaf mineral composition was analysed and found to be correlated with crop load. ‘Hass’ leaves had significantly higher levels of B, Ca, Mg, Na, P and K than ‘Ettinger’ leaves. Rootstocks of Mexican origin produced higher foliar Cl levels, but lower levels of Mg and Mn. Rootstocks grown from seedlings conferred higher foliar K and lower B, Ca and Mg. The results demonstrate that avocado rootstocks affect the nutritional status of the tree, by a differential mineral transport, which is indicated by the scion leaf ionome.     

酸铝胁迫对栝楼根系生长及铝积累的影响

针对南方酸性红壤对作物的生长造成的不利影响,采用水培方式,研究酸铝环境0、100、300、500、1000μmol·L-1Al3＋pH4.5,处理7d对长兴栝楼根系生长及铝积累的影响。测定指标包括根系活力、质膜透性、抗氧化酶类活性（过氧化物酶POD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX、愈创木酚过氧化物酶GPX、超氧化物歧化酶SOD）及其同工酶、过氧化氢（H2O2）含量、根尖铝含量的影响。结果表明：随着铝处理浓度升高,根系活力增大,根系质膜透性无显著变化;POD、CAT、APX酶活升高,GPX和SOD活性降低,多种抗氧化酶都有多条同工酶谱带出现;根尖相对铝含量升高,桑色素染色情况显示,荧光梯度与铝含量测定结果一致,并观察到根尖以上根毛处细胞凸起较之平整排列的根细胞更容易积累铝。栝楼对南方酸性红壤具有较强的适应能力,其体内抗氧化酶系统及根尖吸收、积累铝的机制对缓解铝毒害起着重要作用。     

Activities of Iron‐Containing Enzymes in Leaves of Two Tomato Genotypes Differing in Their Resistance to Fe Chlorosis

Abstract

Two tomato (Lycopersicon esculentum Mill., cvs. Pakmor and Target) genotypes differing in resistance to iron (Fe) deficiency were grown in nutrient solution under controlled environmental conditions over 50 days to study the relationships between severity of leaf chlorosis, total concentration of Fe, and activities of Fe‐containing enzymes in leaves. The activities of Fe‐containing enzymes ascorbate peroxidase, catalase, and guaiacol peroxidase, and additionaly the activity of glutathione reductase, an enzyme that does not contain Fe, were measured. Plants were supplied with 2 × 10^?7 M (Fe deficient) and 10^?4 M (Fe sufficient) FeEDTA, respectively. Leaf chlorosis appeared more rapidly and severely in Target (Fe deficiency senstive genotype) than Pakmor (Fe deficiency resistant genotype). On day 50, Pakmor had 2‐fold more chlorophyll than Target under Fe deficiency, while at adequate supply of Fe the two genotypes were very similar in chlorophyll concentration. Despite distinct differences in development of leaf chlorosis and chlorophyll concentrations, Pakmor and Target were very similar in concentrations of total Fe under Fe deficiency. In contrast to Fe concentration, activities of Fe‐containing enzymes were closely related to the severity of leaf chlorosis. The Fe‐containing enzymes studied, especially catalase, showed a close relationship with the concentration of chlorophyll and thus differential sensitivity of tomato genotypes to Fe deficiency. Glutathione reductase did not show relationship between Fe deficiency chlorosis and enzyme activity. The results confirm that measurement of Fe‐containing enzymes in leaves is more reliable than the total concentration of Fe for characterization of Fe nutritional status of plants and for assessing genotypical differences in resistance to Fe deficiency. It appears that Fe deficiency‐resistant genotype contains more physiologically available Fe in tissues than the genotype with high sensitivity to Fe deficiency.     

Response of Cherry Rootstocks to Boron and Salinity

ABSTRACT

The objective of the present research was to study the effects of boron (B) and potassium chloride (KCl) induced salinity on growth, nutritional status, and chlorophyll content of the cherry rootstocks CAB 6P (Prunus cerasus L.) and Gisela 5 (Prunus cerasus L. × Prunus canescens L.). Plants produced the longest shoots, more leaves, and the greatest fresh weights of shoots and leaves when treated with 0.025 mM B combined with the lower level of salinity (0.75 dS m^?1). CAB 6P plants retained most of their leaves until the end of the experiment, whereas Gisela 5 plants showed higher leaf shedding. Irrigation of plants with solutions containing 0.2 mM B and electrical conductivities (EC) of 4 dS m^?1 resulted in lower leaf chlorophyll contents (SPAD units) when compared with all other treatments. Nitrogen (N) concentrations of leaves from both rootstocks decreased as the EC of the nutrient solution increased from 0.75 to 4 mM. Potassium (K) concentrations of leaves from both rootstocks increased as salinity levels increased.     

Nutritional (Fe-Mn) interactions in ‘Big Top’ peach plants as influenced by the rootstock and by the soil CaCO3 concentration

Manganese (Mn) toxicity in plants is often not a clearly identifiable disorder and it can interfere with the absorption, translocation, and utilization of other elements such as Ca, Mg, Fe, and P. Soil conditions, management factors, and the use of different genotypes of rootstock can determine the degree of Mn toxicity and of interaction with other elements in the orchard. Five plants of the cultivar ‘Big Top’® grafted onto itself, onto plum rootstock ‘Mr.S.2/5’ and onto hybrid peach x almond rootstock ‘GF677’ were grown in 25-L containers under three treatments, 0, 20, 30% concentration of total lime, obtained by mixing powdered CaCO₃ to a sandy soil. Plants were fertilized with manure and a solid fertilizer early in April and irrigated in summer periodically with water rich in manganese. After just 28 d, active lime caused a decrease of chlorophyll SPAD index especially in plants grafted on itself, while those grafted on the tolerant ‘GF677’ rootstock behaved better than those grafted on ‘Mr.S.2/5.’ From June to September, irrigation caused increases in soil Mn concentration and Mn concentration in control plants. This caused first a serious defoliation in Big Top / Big Top plants and then a re-greening of cultivar grafted onto ‘Mr.S.2/5’ and ‘GF677,’ probably due to the interaction between iron and manganese at high pH. In particular the 20% CaCO₃ addition to the soil preserved the plants of cultivar grafted onto ‘Mr.S.2/5’ from Mn toxicity, as shown by their high chlorophyll content and growth and lower Mn leaf concentrations. Plants grafted onto ‘GF677’ rootstock showed the best behaviour under 30% CaCO₃ treatment associated to higher Fe(III)-reducing capacity and photosynthetic activity. Rootstocks and soil conditions (lime and waterlogging) influenced mineral status and growth of the peach cultivar ‘Big Top,’ particularly by interacting together and modifying Fe-Mn availability.     

Citrus rootstock and carbon dioxide enriched irrigation influence on seedling emergence,growth, and nutrient content 1

Seeds of Carrizo citrange (Citrus senensis (L.) Osb. X Poncirus trifolliata (L.), Cleopatra mandarin (C. reticulata Blanco), Sour orange (C. aurantium L.), and Rough lemon (C. Union (Buna f.) were sown in trays, irrigated without or with enriched Carbon dioxide (CO₂) (1,362 mg L^‐1) and evaluated for seedling emergence, growth, and nutrient contents. Rough lemon had a faster rate and higher percent emergence than the other rootstocks. Carrizo citrange had thicker stem diameters and taller seedlings than other rootstocks. Cleopatra mandarin had the smallest seedling shoot and root weights and larger shootrroot ratios than Rough lemon and Sour orange. Carrizo citrange and Cleopatra mandarin had higher leaf chlorophyll‐a and total chlorophyll content than Rough lemon or Sour orange. Carbon dioxide enriched irrigation had no effects on emergence or seedling growth variables except lower root weight. Lower media pH (6.90 versus 5.65), attributed to CO₂ enriched irrigation, may have adversely affected root growth as compared to shoot characteristics. Leaf nutrient contents generally differed between rootstocks but were not affected by CO₂ enriched water except for higher Zn and lower Mn contents. These results indicate that citrus seedling emergence, subsequent growth and leaf nutrient content differred between rootstocks but there are no beneficial effect from CO₂ enriched irrigation.     

Adaptation of Medicago sativa cv. Gabès to long‐term NaCl stress

The perennial Medicago sativa cv. Gabès is widely grown on saline soils in Tunisian oases. The mechanisms by which this NaCl‐tolerant cultivar maintains a positive growth balance were analyzed. In this plant of considerable agronomic interest, biochemical analyses were conducted in order to study the effects of salinity on mature leaves. Free‐radical detoxification mechanisms and changes induced by the accumulation of reactive oxygen species (ROS) in response to the NaCl stress were compared between the upper (young) and lower (old) carbohydrate source leaves. Long‐term NaCl (150 mM) treatment significantly reduced the size of source leaves supporting growth. Salinity damage was greater in the lower than in the upper leaves. This damage was associated with a high Na⁺ : K⁺ ratio and a decrease in the activity of H₂O₂‐scavenging enzymes, leading to lipid peroxidation. In lower source leaves that were mainly affected by ionic stress, superoxide dismutase (SOD) was overexpressed and guaiacol peroxidase (GPX) activity increased. In contrast, in upper source leaves that were mainly exposed to water deficit, catalase and ascorbate peroxidase (APX) activities increased whereas GPX activity was unchanged. The upper source leaves maintained adequate ionic and water status and an efficient ROS detoxification, allowing sinks to be supplied with photoassimilates and maintaining a positive growth balance in this cultivar of alfalfa.     

Significance of Nickel Supply for Growth and Chlorophyll Content of Wheat Supplied with Urea or Ammonium Nitrate

ABSTRACT

Nickel (Ni) is an essential element for activation of urease in higher plants. The effects of Ni as an essential micronutrient on growth and chlorophyll content of wheat plants grew in nutrient solutions supplied either with ammonium nitrate or urea as two different nitrogen (N) sources were investigated. Plants were allowed to grow for six weeks, then leaf chlorophyll content, shoot and root fresh and dry weights, and Ni concentration in shoots and roots were determined. Shoot and root Ni concentration in both urea and ammonium nitrate-fed plants increased significantly with the increase in Ni concentration. Growth and chlorophyll content in leaves of the urea-fed plants increased when Ni concentration in the solution was as high as 0.05 mg L^?1 and decreased at 0.1 mg Ni L^?1. In ammonium nitrate-fed plants, these parameters increased up to 0.01 mg Ni L^?1 and started to decrease with further increase in Ni concentration. Plants that grew in nutrient solutions containing urea had more shoots and roots fresh and dry weight at third and fourth Ni levels (0.05 and 0.1 mg L^?1) than those that grew in media containing ammonium nitrate with similar Ni levels. Total chlorophyll content was also higher in plants supplied with urea plus Ni. The amount of Ni required for optimum wheat growth was dependent on the forms of N used. When supplied with ammonium nitrate or urea, the amount of Ni needed was 0.01 and 0.05 mgL^?1 of nutrient solutions, respectively.     

Nitrogen‐use efficiency traits of mini‐watermelon in response to grafting and nitrogen‐fertilization doses

Two experiments were conducted to study the effect of grafting on nitrogen‐use efficiency (NUE) in mini‐watermelon plants. In the first study, mini‐watermelon plants (Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita (Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root‐to‐shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO$ _3^- $ ). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini‐watermelon plants was evaluated under field conditions. In the hydroponic experiment mini‐watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO₃) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO$ _3^- $ , mini‐watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO$ _3^- $ . The open‐field study indicated that increasing N‐fertilization rates from 0 to 100 kg ha^–1 improved total and marketable yields of mini‐watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N‐uptake efficiency, and N‐utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini‐watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.     

The role of antioxidative metabolism of tomato leaves in long‐term salt‐stress response

The antioxidative protection system as adaptation strategy to high soil salinity in the leaves of two tomato (Lycopersicon esculentum Mill.) hybrids (Buran F1 and Berberana F1) was investigated. Changes in the activity of superoxide‐dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), as well as total and oxidized ascorbate concentrations (AA and DHA) in the plant leaves subjected to three salinity levels (EC 3.80 dS m⁻¹, 6.95 dS m⁻¹, and 9.12 dS m⁻¹) relative to non‐saline control were analyzed during the fruiting phase. The obtained results clearly indicate a relation between SOD activity and AA concentration in the antioxidative protection without any peroxidase‐related H₂O₂ detoxification. Increased SOD activity accompanied by high AA concentration was noticed at all salinity levels, but the response of hybrids was specific for the particular salt concentration. The first salinity level (EC 3.80 dS m⁻¹) induced the highest level of AA in the Buran F1 (70%), while in Berberana F1 hybrid leaves the highest AA concentration (64%) was noticed at the third salinity level (9.12 dS m⁻¹). All salinity levels caused a decline in POD and APX activities in both hybrids. The possibility of a predominant role of ascorbate and SOD in the antioxidative protection of mature tomato leaves under long‐term salt stress is discussed.