Abstract: Mn deficiency is a common nutritional disorder affecting the growth, yield and fruit quality of citrus plants. Twenty-three-year-old 'Washington Navel' orange (Citrus sinensis L.) trees budded onto sour orange (C. aurantium L.) rootstock and grown in two sites (I and II) of an orchard were used. Based on the leaf Mn concentrations, 20 Mn deficient and 10 non Mn deficient trees were selected on 26 January 2000. The trees were separated in 6 groups; each one consisted of 5 trees with similar Mn status. The mean Mn concentrations in the leaves of the groups 1, 2, 3, 4, 5, and 6 were 8.8, 10.5, 11.2, 13.8, 18.3, and 19.8 mg kg(-1) dry weight (d.w.), respectively. The trees of the groups 1-4 were grown in the site I, while those of the groups 5 and 6 in the site II of the orchard. One tree group in each orchard site (site I: group 3; site II: group 6) was not sprayed with Mn and used as a control, while the trees of the other groups (1, 2, 4 and 5) were sprayed on 06 February 2000 with MnSO4-H2O (800 mg 1(-1) Mn). From 18 February 2000 until 19 January 2001, 11 leaf samplings were conducted to monitor the Mn status of the trees. The concentrations of Mn in the leaves of the groups 3 and 6 (controls) were almost constant and presented no significant differences among the samplings. With regard to the Mn treated trees, at the first post-treatment sampling (18 February 2000), the leaf Mn levels were higher by 16.5-25.1 mg kg(-1) d.w., respectively, in relation to their pre-treatment status. At the last sampling (19 January 2001), the Mn status of the trees was also improved by 4.5-7.5 mg kg(-1) (d.w.), compared to their pre-treatment status. Overall, when the concentration of Mn in the leaves is equal or higher than 14 mg kg(-1) d.w., before the spray Mn treatment, only one application of MnSO4-H2O (800 Mg 1(-1) Mn) on February is sufficient to cover the Mn needs of the trees for a whole year. In other cases (leaf Mn levels equal or lower than 13 mg kg(-1) d.w.), the trees should be re-sprayed on July or August.

Abstract: We investigated the uptake of aluminum (Al) and transport to shoots in two inbred maize lines (Zea mays L., VA-22 and A(4/67)) differing in At tolerance. Seedlings were grown for 7 days in hydroponic culture with nutrient solution that contained 0, 240, 360, and 480 mu M Al at pH 4.2. After 7 days of exposure to Al, roots of sensitive maize line (A4/67) plants accumulated 2-2.5 times more At than roots of tolerant line (VA-22) plants. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the tolerant line retained higher concentrations of Ca2+ , Mg2+, and K+ compared with the sensitive line. In response to At treatment, proline (Pro) concentration increased three-fold in roots of tolerant plants, while a slight increase was observed in roots of sensitive-tine plants. A substantial carbon surplus (two-fold increase) was observed in roots of the At-tolerant maize line. Carbohydrate concentration remained almost unchanged in roots of At-sensitive tine plants. At treatment triggered the enhancement of lipid peroxidation in the sensitive line, while no change in lipid peroxidation level was observed in the tolerant maize line. These data provide further support to the hypothesis that a mechanism exists that excludes At from the roots of the tolerant maize line, as well as, a internal mechanism of tolerance that minimizes accumulation of lipid peroxides through a higher Pro and carbohydrate content related to osmoregulation and membrane stabilization. (C) 2007 Elsevier GmbH. All rights reserved.

Abstract: Since citrus fruits are non-climacteric, commercial harvest for a given variety can occur over a prolonged period in the same orchard. Delayed citrus harvest has previously been reported to influence fruit quality variables during the current season and to reduce the subsequent year’s yield. The aim of our study was to investigate the effect of harvest date on tree yield and fruit quality of two late-maturing Valencia orange varieties during two successive years. Materials and methods. One hundred 9-year-old Campbell and Lue Gim Gong Valencia orange trees budded on Swingle citrumelo rootstock were used. Fruit sampling included fruit harvest at five monthly intervals (April-August) during 2003, and only one harvest date (20 June) during 2004. Results and discussion. Based on seasonal variation of various fruit quality variables during the five harvests conducted in 2003, the most stable fruit quality variables were fruit weight, number of seeds per fruit, rind thickness, juice content and soluble solids content. In general, both varieties produced fruit with similar internal quality characteristics. However, their mean fruit weight differed in 2004 (Lue Gim Gong had larger fruit than Campbell). Furthermore, the annual and cumulative yields of Lue Gim Gong Valencia orange trees over two years were significantly higher than those of Campbell orange trees. Finally, the yield per tree and fruit quality of both varieties in 2003 and 2004 were not affected significantly by the date of harvest during 2003.

Abstract: The effect of salinity on the non-enzymic and enzymic antioxidant activity, shoot proliferation and nutrient accumulation was studied in in vitro cultures of the rootstock CAB-6P (Prunus cerasus L.). Three concentrations (0, 30 and 60 mM) of NaCl or CaCl2 were added to a modified MS medium. Between the two salt treatments used, only the explants treated with CaCl2 presented significant decrease in growth parameters. The concentrations of Na+ and Cl- in the explants treated with NaCl were increased, as NaCl in the culture medium increased. Furthermore, in the explants treated with CaCl2 the concentrations of Ca2+ and Cl- were increased while that of K+ decreased, as CaCl2 concentration increased. The activity of peroxidase in leaves as well as the number of its anionic isoforms was increased under 30 mM CaCl2 as well as 60 mM NaCl or CaCl2. On the contrary, increasing salinity, from 0 to 60 mM CaCl2, resulted in a reduction of the catalase activity in leaves followed by disappearance of the only one catalase isoform that was detected in leaves (60 mM CaCl2). In the stems of the explants treated with NaCl the peroxidase activity was reduced. In the stems and leaves of the explants grown in saline substrate the non-enzymic antioxidant activity was significantly increased. The results suggest that the stems and leaves of CAB-6P explants presented variable antioxidant responses that were depended on the salt form used. The contribution of enzymic and non-enzymic protection mechanisms to the adaptation of CAB-6P explants under salinity stress is discussed.

Abstract: Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 mu M Mn (Nino, Mn-2, Mn-14, Mn-98, and Mn-686, respectively). To adequately investigate the combined effects of Mn nutrition and irradiance on photosystem 2 (PS2) activity, irradiance response curves for electron transport rate (ETR), nonphotochemical quenching (qN), photochemical quenching (q(p)), and real photochemical efficiency of PS2 ((Phi(PS2)) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1211, 1911, and 3 111 mu mol m(-2) s(-1), I-66 to I-3111, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn-686) compared to Nino; its highest values were recorded in the treatments Mn-2-Mn-98. However, ETR and (Phi(PS2) values were significantly lower under Mn-0 compared to the other Mn treatments, when plants were exposed to irradiances 96 mu mol m(2) s(-1). Furthermore, Nino plants had significantly higher values of qN and lower values of qp at irradiances >= 226 and >= 336 mu mol m(-2) s(-1), respectively, than those grown under Mn-2-Mn-686. Irrespective of Mn treatment, the values of (Phi(PS2) and qN decreased, while those of qp increased progressively by increasing irradiance from I-136 to I-3111. Finally, Mn2-Mn98 plants were less sensitive to photoinhibition of photosynthesis (>= 811 pmol m(-2) s-) than the Mn686 (>= 536 mu mol ih 2 s(-1)) and Nino (> 336 mu mol m(-2) s(-1)) ones.

Abstract: Seedlings of Citrus volkameriona (L.) were grown hydroponically for 43 days in order to study the effect of Mn concentration (0, 2, 14, 98 and 686 mu M) in the nutrient solution on leaf anatomy and mesophyll chloroplast ultrastructure. Increasing Mn concentration stimulated Leaf Lamina thickness. The size of mesophytt chloroplasts decreased and increased under 0 and 686 mu M Mn, respectively, compared to the intermediate Mn concentrations, similar with regard to the number of chloroptasts per mesophytt cell area. Thylakoid membranes of plants grown under 0 mu M Mn were somewhat swelled, white those in other Mn treatments did not present any visible malformation. The relative volume of starch grains per chloroplast was significantly smaller under 0-98 mu M Mn (12.8-16.0%) than in the treatment with 686 mu M Mn (67.6%). Further, under 686 mu M Mn, dark deposits were found in vacuoles. The existence of a cell adaptation mechanism to excessive Mn availability (686 mu M Mn) by increasing the size of chloroplasts as welt as their number per cellular area, is discussed. (c) 2006 Elsevier GrnbH. All rights reserved.

Abstract: Gardenia (Gardenia jasminoides) plants were grown in black plastic bags containing perlite and sand (1:1). The plants were irrigated with 16 modified half strength Hoagland No2 nutrient solutions containing four Fe concentrations (0, 0.5, 1 and 2 mg L-1) in the form of Fe-EDDHA (Fe 6g 100g-1) in combination with four P concentrations (0, 31, 62 and 124 mg L-1). Increasing P and Fe concentrations in the nutrient solution significantly increased leaf P and K concentrations. However, leaf Ca concentration was slightly decreased by increasing P concentration in the nutrient solution. No significant effects of P and Fe concentration were found concerning leaf Mg and Mn concentrations. Furthermore, the leaf Zn concentrations in plants treated with 0, 31 and 62 mg L-1 P and 0 mg L-1 Fe were significantly increased. By increasing Fe concentration in the treatments containing 62 and 124 mg L-1 P, leaf Fe concentration was increased. In gardenia roots, the increase of P and Fe concentration in the nutrient solution led to a general increase of root P concentration. Concerning Ca, it was significantly increased in the roots, when P concentration in the nutrient solution increased. There were no significant effects of P and Fe concentration of solution in Mg concentration of roots. Manganese and Zn concentration in roots was only increased in plants treated with 124 mg L-1 P plus 0 or 0.5 mg L-1 Fe. Finally, not significant differences were recorded in root Fe concentration among the studied treatments. In conclusion, the combined PxFe fertilization in gardenia may solve also other nutritional problems like K, Ca and Zn deficiencies.

Abstract: Growth, mineral nutrition, leaf chlorophyll and water relationships were studied in cherry plants (cv. 'Bigarreau Burlat' [BB] and 'Tragana Edessis' [TE]) grafted on 'Mazzard' rootstock and grown in modified Hoagland solutions containing 0, 25 or 50 mmol L-1 NaCl, over a period of 55 days. Elongation of the main shoot of the plants treated with 25 or 50 mmol L-1 NaCl was significantly reduced by approximately 29-36%, irrespective of the cultivar. However, both NaCl treatments caused a greater reduction in the dry weight of leaves and scion's stems in BB than in TE plants. Therefore, BB was more sensitive to salinity stress than TE. The reduction of leaf chlorophyll concentration was significant only when BB and TE plants were grown under 50 mmol L-1 NaCl. Osmotic adjustment permitted the maintenance of leaf turgor in TE plants and induced an increase in leaf turgor of BB plants treated with 25 or 50 mmol L-1 NaCl compared with 0 mmol L-1 NaCl. Concerning the nutrient composition of various plant parts, Na concentrations in all plant parts of both cultivars were generally much lower than those of Cl. For both cultivars, leaf Cl concentrations were much higher than the concentrations in stems and roots, especially in the treatments containing NaCl. Finally, the distribution of Na within BB and TE plants treated with NaCl was relatively uniform.

Abstract: The effectiveness of the calcium products Chelan, Power-Ca, and calcium chloride to reduce the development of Monilinia laxa on 'Andross' peach (Prunus persica) was investigated. The mycelium growth of M. laxa on potato dextrose agar modified with Chelan, Power-Ca, or calcium chloride compound at concentrations 1, 2, and 4 g(.)L(-1) was significantly reduced in comparison with the water. Chelan, Power-Ca, and calcium chloride applied as foliar sprays did not significantly affect the development of the pathogen on inoculated immature and mature peaches. However, dipping peaches in solutions containing one of the calcium products tested reduced significantly the percentage of M. laxa infection on inoculated fruit.

Abstract: Microshoots of Citrus maxima (Burm.) Merr. were cultured in vitro for 75 days in a modified MS rooting medium containing 1.5 mg l(-1) NAA (naphthaleneacetic acid) and 0, 1.37, 2.74, 5.48 or 10.96 mg l(-1) Mn. Small pieces from two regions, i.e. 5-10 mm and 30-35 mm behind the apex, of adventitious roots were examined by light microscopy. Various root growth parameters and the carbohydrate contents of shoots and roots were also measured. The diameters of root cortex and stele progressively decreased as Mn concentration in the medium increased. Shoot explants grown without Mn (0 mg l(-1) Mn) formed shorter and thicker roots when compared to those treated with Mn (1.37-10.96 mg l(-1)). The diameter of roots in the 10.96 mg l(-1) Mn treatment was smaller compared to the other Mn treatments, although the mean length of roots did not differ among the 1.37, 2.74, and 10.96 mg l(-1) Mn treatments considerably. The greatest root length was observed in 5.48 mg l(-1) Mn. However, the total length of roots formed per microshoot in 0 and 10.96 mg l(-1) Mn was significantly smaller than that in 1.37-5.48 mg l(-1) Mn. The carbohydrate content (mu mol) of the roots was higher in 1.37-5.48 mg l(-1) Mn than in 0 and 10.96 mg l(-1) Mn.

Abstract: Leaf samples of Mn-deficient and Mn-sufficient (control) 'Navelate' orange plants grown in a greenhouse were taken to investigate the effects of Mn deficiency in leaf structure and chloroplast ultrastructure. Total leaf chlorophyll concentration was significantly lower in Mn-deficient plants than in control ones. Entire lamina thickness was not altered due to Mn deficiency. However, Mn deficiency resulted in disorganization of mesophyll cells, mainly of palisade parenchyma cells. The number of mesophyll chloroplasts per cellular area and their length were both affected negatively. The membranous system of chloroplasts was also disorganized. The percentages of starch grains and plastoglobuli per chloroplast of Mn-deficient leaves were significantly greater than those of control leaves.

Abstract: The objective of this research was to study the effect of the chelated form of the iron salt of ethylenediamine di-o-hydroxyphenylacetic acid (Fe-EDDHA) (6% Fe) on in vitro rooting of the rootstock GF-677. The iron salt of ethylenediamine tetraacetic acid (Fe-EDTA) (12% Fe) of the MS basic medium was replaced by Fe- EDDHA, which was applied in three concentrations: 93.5, 187.0 and 280 mg l(-1) (5.6, 11.2 and 16.8 mg l(-1) Fe, respectively). For each treatment of Fe- EDDHA, the effect of ascorbic acid added in four concentrations ( 0, 0.1, 1.0 and 10 mg l(-1)) was studied. After 4 weeks of culture, the explants growing on the medium with 280 mg l(-1) Fe- EDDHA gave the best rooting results. Regarding ascorbic acid, no clear stimulating effect on rooting was found.

Abstract: black plastic bags containing a sand/perlite ( 1: 1) mixture. The plants were irrigated with Hoagland No2 nutrient solution modified to contain three Fe concentrations (0.5, 1 and 2 mg l(-1)) in the form of Fe-EDDHA and four concentrations of NaCl ( 0, 10, 20 and 40 mM). After three months, severe toxicity symptoms were observed on the older leaves ( chlorosis of tips and margins) mainly of the plants treated with 40 mM NaCl. Salinity had little effect on leaf P, whereas P concentration of roots increased in the treatments containing 20 or 40 mM NaCl plus 0.5 mg l(-1) Fe. Generally, K and Ca concentrations of leaves and roots were not affected by the increase of NaCl concentration in the nutrient solution. In the roots, the lowest Mg concentration was observed in the treatments containing 2 mg l(-1) Fe, whereas in the leaves, no significant differences were recorded. Regarding Mn concentration, it was not affected in the leaves but it increased in the roots of the treatments containing 20 and 40 mM NaCl plus 0.5 mg l(-1) Fe. Finally, Fe concentration was increased in the roots of the plants treated with 0.5 mg l(-1) Fe plus 20 or 40 mM NaCl. Concerning Na concentration, generally, it was increased in the leaves and decreased in the roots of the treatments containing high NaCl plus low or medium Fe concentration.

Abstract: Two experiments were conducted in Northern Greece during 2004-2005 with the clingstone peach cv. Andross. From our results, it was concluded that fruit firmness and fruit Ca were increased, while K/Ca and K/Ca+Mg ratios decreased, after soil incorporation of ammonium nitrosulfate plus ammonium nitrate followed by foliar sprays with 0-12-14. Fruit Ca was increased and the K/Ca and (K+Mg)/Ca ratios decreased by gypsum and foliar CaCl2.2H(2)O or Ca-chelate treatments, when ammonium nitrosulfate plus ammonium nitrate were applied. When calcium nitrate was applied, fruit Ca was significantly increased by CaCl2.2H(2)O in comparison to gypsum application, while fruit K/Ca and K+Mg/Ca ratios significantly were decreased by CaCl2.2H(2)O as with 0-12-14 foliar sprays in comparison to control treatments. Also, fruit Ca was higher and the K/Ca and the K+Mg/Ca ratios were lower. when calcium nitrate was added instead of ammonium nitrosulfate plus ammonium nitrate (control treatments - I). For overall values, fruit firmness was significantly and positively correlated with fruit Ca concentration (r=0.436*) and negatively with K/Ca and (K+Mg)/Ca ratios in fruits (r=-0,421* and r=-0,389*, respectively).

Abstract: The in vitro response of the apple rootstocks M 9 and MM 106 to increasing concentrations of sucrose (44, 88, 176 mM) and sorbitol (82, 164, 329 mM) of the culture medium is reported. 88 mM sucrose in the MS medium was the optimal concentration for shoot proliferation of shoots of both the rootstocks as compared to 44 and 176 mM. By increasing sucrose concentration of the medium, shoot length of MM 106 plants increased. However, the effect of the tested sucrose concentrations on shoot length of M 9 plants was not apparent. The in vitro cultures of M 9 shoots produced the greatest number of shoots and the longest shoots per explant with 164 mM of sorbitol in the medium as compared to 82 and 329 mM sorbitol, and to all sucrose concentrations tested. However, the in vitro cultures of MM 106 produced the highest fresh weight per explant, the greatest number of new shoots and the longest shoots per explant with 329 mM of sorbitol in the medium compared to all the other treatments, indicating a genotypic effect. Mineral concentration in plants was also a function of genotype, carbohydrate source and its concentration in the medium. Explants of both rootstocks treated with sorbitol showed the highest peroxidase and catalase activities in leaves and stems. Although, no differences were found between the electrophoretic profiles of catalase, however, the presence of sucrose and sorbitol in the MS medium remarkably influenced the population of peroxidase isoenzymes in leaves and stems of both rootstocks.

Abstract: The effect of different Fe sources [FeSO4 center dot 7H(2)O, (NH4)(2)[Fe(SO4)(2)]center dot 6H(2)O, FeEDDHA (ferric ethylenediamine di (o-hydroxyphenylacetic acid)] and concentrations (0.1, 0.2, 0.4 mM Fe) on multiplication and rooting of the pear rootstock OHF 333 in vitro was studied. The length of shoots significantly increased in the presence of 0.2 mM FeSO4 center dot 7H(2)O in comparison to the rest treatments. However, the number of shoots per explant and the fresh mass were significantly increased in the presence of 0.4 mM FeEDDHA. FeEDDHA at all concentrations significantly promoted shoot proliferation in comparison to the rest Fe sources. Explants supplied with 0.1 mM Fe in the form of (NH4)(2)[Fe(SO4)2]center dot 6H(2)O had higher rooting percentage, as well as greater number of roots per explant, root length, and fresh and dry mass of cultures compared to the rest Fe sources. The organic form of Fe (FeEDDHA) resulted in low percentage of rooting compared to the other Fe sources. Explants; grown on media without Fe showed low rooting percentage. Calcium, Mg and B concentrations of plants treated with the various Fe forms were not significantly different compared to the control. By increasing Fe concentration of the culture medium from 0.1 to 0.4 mM, Mn and Zn concentrations of cultures declined.

Abstract: In the present paper, the nutrient concentration of plant organs, when different Fe sources were used in gardenia ( Gardenia jasminoides Ellis) plants grown in a hydroponic medium containing 1 mg l(-1) Fe, was studied. Three Fe sources were applied, namely sequestrene-138 ( 6% Fe, Fe-EDDHA), sequestrene-330 ( 10% Fe, Fe-DTPA) and FeSO4 center dot 7H(2)O. The analytical data indicated that Fe and Zn concentrations in shoots were very low and were independent of the Fe source applied. Furthermore, K concentration of shoots was higher than K concentration of roots. It appears that in roots, the concentrations of Fe and Zn were very high. In roots, the lowest Fe concentration was found in the sequestrene-138-treated plants, whereas the highest one in the plants treated with FeSO4 center dot 7H(2)O.

Abstract: In the present paper, the nutrient concentration of plant organs, when different Fe sources were used in gardenia (Gardenia jasminoides Ellis) plants grown in a hydroponic medium containing 1 mg l–1 Fe, was studied. Three Fe sources were applied, namely sequestrene-138 (6% Fe, Fe-EDDHA), sequestrene-330 (10%Fe, Fe-DTPA) and FeSO4·7H2O. The analytical data indicated that Fe and Zn concentrations in shoots were very low and were independent of the Fe source applied. Furthermore, K concentration of shoots was higher than K concentration of roots. It appears that in roots, the concentrations of Fe and Zn were very high. In roots, the lowest Fe concentration was found in the sequestrene-138-treated plants, whereas the highest one in the plants treated with FeSO4·7H2O.

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. x 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.

Abstract: The objective of this study was the comparison of the effect of two Mn sources (MnSO4-H2O, MnEDTA) which were applied at various concentrations (0, 200, 400, 800, and 1200 mg Mn l(-1)) to the leaves of 'Washington navel' orange trees in order to correct Mn deficiency. One hundred and seventy days after the foliar application of Mn solutions, the mean Mn concentrations in the leaves treated with MnSO4-H2O (200, 400, 800 or 1200 mg Mn l(-1)) or MnEDTA (400, 800 or 1200 mg Mn l(-1)) were significantly higher than those of the control leaves. Manganese sulfate (MnSO(4)center dot H2O) was more effective than MnEDTA regarding the improvement of the leaf Mn concentrations of the trees, when applied at equal Mn concentrations. Finally, the leaf Mn concentrations were in the sufficiency range (> 25 mg kg(-1) d.w.), only after the application of 800 or 1200 mg Mn l(-1) as MnSO(4)center dot H2O. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: The nutrient status [annual fluctuation of leaf nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and zinc (Zn)], yield and fruit quality [soluble solids concentration (SSC), titratable acids (TA), SSS/TA and juice content] of "Encore" mandarin trees cultivated in two sites of the same orchard were studied. The trees were grafted on Carrizo citrange rootstock and grown under identical conditions, apart from some soil properties. Soil B (site B of orchard) contained more K, Ca, Mg, and organic matter than soil A (site A of orchard). The patterns of annual variation of leaf nutrient concentrations were similar in both soils, although leaf concentrations of Ca, Mg, Mn, and Fe in soil A were significantly higher than those of soil B, while leaf K concentrations were significantly lower. The mineral analyses of the leaves revealed some interesting antagonisms between K-Mg, K-Ca, and K-Mn. Manganese deficiency was especially limited in the trees grown in soil B. The average fruit yield per tree in soil A, on two-year basis, was significantly higher than this in soil B. The significantly higher water infiltration rate in soil B, in contrast to soil A, seemed to be the dominant factor responsible for the differences among the two sites in yielding and leaf mineral composition.

Abstract: A greenhouse experiment was carried out in order to study the effects of B excess (2.50 mg B l(-1)) on physiological (B concentration and distribution, gas exchange parameters, chlorophyll concentration and fluorescence) and anatomical (leaf structure and chloroplast ultrastructure) characteristics of 'Navelina' orange plants grafted on sour orange and Swingle citrumelo rootstocks. Boron concentrations of all plant parts increased with increasing B concentration in the nutrient solution, following the order: old leaves > young leaves > bark of rootstock > root > stems of scion > stem of rootstock > wood of rootstock. 'Navelina' plants were less sensitive to excess B when grafted on Swingle citrumelo than on sour orange. This was due to the lesser absorption of B from the nutrient solution and its greater total retention in the rootstock stem of plants grafted on Swingle citrumelo than those grafted on sour orange rootstock, thus limiting the amount of B that reached the leaves of plants grafted on Swingle citrumelo rootstock. Increased B concentration in the nutrient solution brought about a decrease of leaf thickness, mainly due to reduced spongy parenchyma tissue. Although the size of chloroplasts decreased in response to high B concentration in the nutrient solution, their shape was not altered. Excess B further decreased the relative volume of chloroplast thylakoids and increased the relative volume of plastoglobuli. Finally, the leaves of 'Navelina' plants grown under 0.25 mg B l(-1) exhibited higher concentrations of chlorophyll as well as higher values of chlorophyll fluorescence parameters (F-v/F-m, F-v/F-0) and of photosynthetic rates in contrast to the plants grown under 2.50 mg B l(-1). (C) 2003 Elsevier B.V. All rights reserved.

Abstract: The effects of high B concentration in the nutrient solution (2.50 mg B l(-1)) on various morphological and physiological parameters of `Clementine' mandarin plants grafted on sour orange and Swingle citrumelo were investigated. These parameters included plant growth, B estimation, chlorophyll, proline and carbohydrate determinations, gas exchange (photosynthetic rate, stomatal conductance, P-n/C-i ratio) and chlorophyll fluorescence (F-v/F-m and F-v/F-0 ratios). Furthermore, micrographs of leaf structure and chloroplast ultrastructure as well as relevant morphometric assessments were presented. Boron toxicity resulted in a diminution of the proline and carbohydrate concentrations in the leaves, whereas the respective values for the roots were not affected. Boron toxicity also resulted in a decrease of the leaf chlorophyll concentration, photosynthetic rate, stomatal conductance, F-v/F-m, F-v/F-0 and P-n/C-i ratios, entire lamina and spongy parenchyma thickness, size of mesophyll cell chloroplasts, and relative volumes of chloroplast thylakoids and starch grains. Both stomatal and non-stomatal factors were responsible for the reduction of the photosynthetic rate, under B excess. The rootstock was found to play an important role in B toxicity. `Clementine' mandarin plants grafted on sour orange proved to be more sensitive to B toxicity than those grafted on Swingle citrumelo. (C) 2003 Elsevier Ireland Ltd. All rights reserved.

Abstract: A greenhouse experiment was performed to study the effects of boron ( B) on growth, nutrient concentration and distribution, nutrient use efficiency, and total nutrient absorption of 2 citrus genotypes. The experimental layout was a 6 x 2 factorial, with 6 B concentrations (0.05, 0.25, 0.50, 1.00, 2.00, and 5.00 mg/L) on 2 genotypes: the sour orange (Citrus aurantium L.) and the Swingle citrumelo (C. paradisi Macf. x Poncirus trifoliata L.). The plants were grown for 3 months in a B-free sand:perlite (1 : 1) medium that was irrigated with 6 half-strength Hoagland's nutrient solutions. Increasing B supply in the nutrient solution increased the B concentration linearly in all parts of the plant in the following order: basal leaves > top leaves > bark > root > stems > wood. There was no consistent effect of B supply on the concentration of other fundamental elements ( P, K, Ca, Mg, Mn, Zn, Fe). Furthermore, none of the tested B concentrations significantly affected the total plant content and consequently the absorption of any other element. A concentration of 1.00 mg B/L or higher resulted in less B absorption by the Swingle citrumelo than by the sour orange. Furthermore, the Swingle citrumelo has the ability to retain more B in its stems and roots than the sour orange, thus preventing B transport to leaves. Finally, B and Mn use efficiency in both genotypes correlated significantly and negatively with the B supply.