Ioannis E. Papadakis

Response of two citrus genotypes to six boron concentrations: concentration and distribution of nutrients, total absorption, and nutrient use efficiency

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 × 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. × 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 Hoaglands 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.

Mobility of Iron and Manganese within Two Citrus Genotypes after Foliar Applications of Iron Sulfate and Manganese Sulfate

ABSTRACT Seedlings of sour orange (Citrus aurantium L.) and Carrizo citrange (C. sinensis L. cv. Washington navel x Poncirus trifoliata)] were grown in plastic pots containing a sand: perlite mixture and watered with a modified Hoagland No 2 nutrient solution throughout the experiment. Three-months-old plants were divided in three groups and sprayed with 0.018 M iron sulfate (FeSO4 .7H2O), 0.018 M manganese sulfate (MnSO4 .H2O), or deionized water. Two months later, plants were harvested and divided into top leaves that grown after the treatments, basal leaves that existed prior to the treatments, stems that partially came in contact with the spray, and roots. The manganese (Mn) spray resulted in a significant increase of Mn concentrations in top leaves, basal leaves, stems and roots of sour orange, and in top leaves, basal leaves, and stems of Carrizo citrange. The iron (Fe) spray significantly increased the concentrations of Fe in the stems and basal leaves of both genotypes. For both genotypes, transport of Mn from basal (sprayed) leaves to top (unsprayed) ones was found. However, the results of this experiment did not give any evidence neither for Mn translocation from sprayed tissues to roots nor for Fe transport from sprayed tissues to unsprayed ones (top leaves, roots). Mn and Fe were found to be relatively mobile and strictly immobile nutrients, respectively, within citrus plants after their foliar application as sulfate salts.

Leaf anatomy and chloroplast ultrastructure of Mn-deficient orange plants

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.

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 Status, Yield, and Fruit Quality of “Encore” Mandarin Trees Grown in Two Sites of an Orchard with Different Soil Properties

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 boron (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.

IS CHLOROPHYLL FLUORESCENCE TECHNIQUE A USEFUL TOOL TO ASSESS MANGANESE DEFICIENCY AND TOXICITY STRESS IN OLIVE PLANTS

A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (Fv/Fm and Fv/F0 ratios) were recorded every 40 days in the leaves of ‘Kothreiki’ and ‘FS-17’ olive cultivars, which were irrigated with Hoaglands nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the Fv/Fm and Fv/F0 ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the Fv/Fm and Fv/F0 ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g−1 d.w. in ‘FS-17’ and 734 μg g−1 d.w. in ‘Kothreiki’). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g−1 d.w. in ‘FS-17’ and 20 μg g−1 d.w. in ‘Kothreiki’, i.e., a little above of the deficiency range (<20 μg g−1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the Fv/Fm and Fv/F0 ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the Fv/Fm and Fv/F0 ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars).

DIFFERENTIAL RESPONSE OF TWO OLIVE CULTIVARS TO EXCESS MANGANESE

The response of three-month-old rooted cuttings of the olive cultivars ‘Picual’ and ‘Koroneiki’ grown in black plastic bags containing perlite as a substrate to excess manganese (Mn) (640 μM) was studied. The rooted cuttings were irrigated with 50% modified Hoagland nutrient solution. At the end of the experimental period, which lasted 130 days, the total fresh and dry weights, as well as the shoot elongation of ‘Picual’ plants were significantly reduced under excess Mn (640 μM), compared to the control plants (2 μM), whereas the growth of ‘Koroneiki’ plants was similar in both Mn treatments. The tolerance index, which is derived from the ratios between the plant growth data of different treatments and the control one, of ‘Picual’ plants to excess Mn was about half of this of ‘Koroneiki’ plants. In both cultivars, the concentrations of Mn in various plant parts (root, basal stem, top stem, basal leaves, top leaves) were significantly increased as Mn concentration in the nutrient solution increased. Furthermore, in the 640 μM Mn treatment, 2 to 2.5-fold greater Mn concentrations were recorded in almost all plant parts of ‘Koroneiki’, than those of ‘Picual’. Similar results were recorded with regard to the total Mn content per plant (‘Koroneiki’ absorbed much more Mn from the nutrient solution than ‘Picual’). On the other hand, excess Mn negatively affected the absorption of iron (Fe), calcium (Ca), magnesium (Mg), phosphorus (P), zinc (Zn), and boron (B), depending on the olive cultivar. In both cultivars, while the Mn use efficiency was significantly decreased under excess Mn conditions, the nutrient use efficiencies of P, Ca, and Fe were significantly increased, compared to the control plants (2 μM Mn). It was also found that excess Mn resulted in a significant increase of stomatal conductance and transpiration rate of both cultivars, whereas the photosynthetic rate was significantly increased only in ‘Koroneiki’. In ‘Picual’, similar photosynthetic rates were recorded in both Mn treatments. The measurement of the various chlorophyll fluorescence parameters, Fv/Fm and Fv/F0 ratios, revealed that the functional integrity of photosystem II (PSII) of photosynthesis was not affected due to excess Mn, irrespectively of the cultivar. In conclusion, although ‘Koroneiki’ tissues had much higher Mn concentrations than those of ‘Picual’, the parameters related to the growth and photosynthetic performance of plants indicates that the internal tolerance of ‘Koroneiki’ tissues to excess Mn was higher than this of ‘Picual’.

Photosystem 2 activity of Citrus volkameriana (L.) leaves as affected by Mn nutrition and irradiance

Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 µM Mn (Mn0, Mn2, Mn14, Mn98, and Mn686, 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 (qP), and real photochemical efficiency of PS2 (ΦPS2) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1 211, 1 911, and 3 111 µmol m−2 s−1, I66 to I3111, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn686) compared to Mn0; its highest values were recorded in the treatments Mn2-Mn98. However, ETR and ΦPS2 values were significantly lower under Mn0 compared to the other Mn treatments, when plants were exposed to irradiances ≥96 µmol m−2 s−1. Furthermore, Mn0 plants had significantly higher values of qN and lower values of qP at irradiances ≤226 and ≥336 µmol m−2 s−1, respectively, than those grown under Mn2-Mn686. Irrespective of Mn treatment, the values of ΦPS2 and qN decreased, while those of qP increased progressively by increasing irradiance from I136 to I3111. Finally, Mn2-Mn98 plants were less sensitive to photoinhibition of photosynthesis (≥811 µmol m−2 s−1) than the Mn686 (≥536 µmol m−2 s−1) and Mn0 (≥336 µmol m−2 s−1) ones.

Growth, mineral composition, leaf chlorophyll and water relationships of two cherry varieties under NaCl-induced salinity stress

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 scions 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.

Effect of calcium on the ion status and growth performance of a citrus rootstock grown under NaCl stress

Abstract Two-year-old own-rooted sour orange (Citrus aurantium L.) plants grown in a greenhouse were irrigated for 15 weeks with Hoagland nutrient solutions containing either NaCl (0, 20, 40, 60, 80 or 100 mmol L−1) or a combination of salts NaCl + CaCl2·2H2O (10 + 10 mmol L−1, 20 + 20 mmol L−1, 30 + 30 mmol L−1, 40 + 40 mmol L−1 and 50 + 50 mmol L−1). The effect of the combined treatments on vegetative growth (fresh matter) was similar to the effect of NaCl. Salinity did not affect the leaf water potential, but did significantly increase the water content of the leaves and the shoot : root ratio (fresh matter). Furthermore, the N concentration of the leaves and the Mg concentration of the new stems were reduced, whereas the K concentrations of the leaves increased. Salinity led to a general increase in Na and Cl concentrations in all plant parts. Chloride concentrations were significantly greater than the corresponding Na values in all tissues. Little or no effect of salinity was recorded with regard to the P, Fe, Mn and Zn concentrations. The addition of Ca to the nutrient solution in the form of CaCl2·2H2O decreased the Na and Cl concentrations in the leaves. Thus, the application of CaCl2·2H2O might mitigate the accumulation of these toxic ions caused by NaCl.