EFFECT OF CITRUS ROOTSTOCKS ON LEAF MINERAL COMPOSITION OF ‘OKITSU’, ‘CLAUSELLINA’, AND ‘SILVERHILL’ MANDARIN CULTIVARS

Citrus performance is strongly related with rootstock. This study was conducted to investigate leaf nutrient contents of ‘Okitsu’, ‘Clausellina’ and ‘Silverhill’ mandarin cultivars budded onto sour orange, ‘Carrizo’ and ‘Troyer’ citrange rootstocks in Dörtyol, Turkey in 2004 and 2005. The maximum nitrogen (N), potassium (K), and copper (Cu) contents were determined for ‘Clausellina’; phosphorus (P) for ‘Okitsu’; and sodium (Na) for ‘Silverhill’. Calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and zinc (Zn) uptake were similar for the mandarin cultivars. ‘Carrizo’ citrange at N, K, Mg, Mn, and Cu uptake; ‘Troyer’ citrange at N, P, K, and Fe uptake; and common sour orange at Ca, Zn, and Na uptake was superior on the other rootstocks. It was observed that ‘Carrizo’ and ‘Troyer’ citrange rootstocks had advantages over sour orange in nutrient uptake. Thus, growth performance, yield, and quality parameters considered, ‘Carrizo’ and/or ‘Troyer’ citranges could be suggested as rootstocks for the studied mandarin cultivars under similar ecological conditions.     

LEAF MINERAL COMPOSITION OF ‘NOVA’, ‘ROBINSON’ AND ‘FREMONT’ MANDARIN CULTIVARS ON DIFFERENT ROOTSTOCKS

Rootstock selection has a critical importance for mineral nutrition of budded cultivars. This study was conducted at the experimental farm of Mustafa Kemal University, Dörtyol, Turkey. The aim of this study was to investigate the effect of sour orange, Troyer and Carrizo citrange rootstocks on the leaf nutrient contents of ‘Nova’, ‘Robinson’, and ‘Fremont’ mandarin cultivars in the 2004 and 2005 growing seasons. Carrizo citrange was examined for nitrogen (N), potassium (K), magnesium (Mg), sodium (Na), and manganese (Mn); Troyer citrange for iron (Fe); and sour orange for calcium (Ca) and zinc (Zn) were superior on the others. Nitrogen, phosphorus (P) and Mg levels of mandarin leaf budded on sour orange were under or just above the deficiency threshold. Potassium, Mn, and Zn content of ‘Robinson’; P, Ca and Fe content of ‘Fremont’; and Cu content of ‘Nova’ were statistically higher. Therefore, it can be concluded that Carrizo rootstock may be suggested for the region and regions with similar ecological conditions.     

Effects of rootstock on the composition of bergamot (Citrus bergamia Risso et Poiteau) essential oil

This paper reports the composition of bergamot oils obtained from plants grafted on the following rootstocks: sour orange, Carrizo citrange, trifoliate orange, Alemow, Volkamerian lemon, and Troyer citrange. The aim of this study is to evaluate the possibility of using rootstocks other than sour orange, checking their effect on the composition of the essential oil. Results are reported for analysis of 203 bergamot oils during the years 1997-1998, 1998-1999, and 1999-2000. The oils were analyzed by HRGC and HRGC/MS; 78 components were identified, and the results were in agreement with those reported in the literature for the Calabrian bergamot oils obtained from industry. Because of the quality of their essential oils, Alemow and Volkamerian lemon can be considered as substitutes for sour orange rootstocks.     

Influence of rootstocks on ‘Orlando’ tangelo leaf elemental concentration

Abstract

The influence of 10 rootstocks on leaf elemental concentrations and their relationship with yield, tree growth, leaf fresh weight and dry matter of ‘Orlando’ tangelo (C. parodisi Macf. x C. reticulata Blanco) was studied under the arid climate of southwestern Arizona. ‘Orlando’ tangelo trees on Carrizo citrange [(C sinensis (L.) Osbeck x Poncirus trifoliata (L.) Raf.], Yuma citrange (P. trifoliata x C. sinensis), Taiwanica (C. taiwanica) and Volkamer lemon (C. limon Burm f.) had larger canopy and higher yield than the trees on Savage citrange (P. trifoliata x C. sinensis), Ichang pummelo (C. ichangensis hyb.) and Palestine sweet lime (C. limettoides Tan.). Leaves of trees on Carrizo citrange were heavier but those on Savage citrange had higher percent dry matter than those on other rootstocks. Trees on macrophylla (Alemow) (C macrophylla Wester) had significantly higher leaf N and Mn while those on Carrizo, Yuma and Savage citranges had lower leaf N than the trees on other rootstocks. Trees on Volkamer lemon, rough lemon (C. jambhiri Lush), macrophylla and Palestine sweet lime had low leaf K but high leaf Mg. ‘Orlando’ trees on Carrizo citrange had the highest leaf Mg and Cu but the lowest leaf Mn. Considering mineral (elemental) uptake efficiency, tree growth and/or yield, Carrizo citrange, Volkamer lemon, Yuma citrange, rough lemon and Taiwanica are desirable for ‘Orlando’ tangelo under the arid conditions and sandy soils of the southwest United States. Macrophylla could only be used for a short term planting, while Savage citrange, Batangas mandarin (C. reticulata Blanco), Ichang pummelo and Palestine sweet lime are not recommended for planting under the arid conditions similar to those of this experiment.     

Iron deficiency stress responses amongst citrus rootstocks

Seedlings of citrus rootstocks differing in lime tolerance were grown in nutrient solution with and without Fe. Proton efflux, release of phenolic compounds and Fe reducing substances and root-mediated reduction of Fe^III in FeEDTA and freshly precipitated Fe(OH)₃ in response to Fe deficiency were determined. Sweet orange, Carrizo citrange and trifoliate orange, the three least tolerant rootstocks used in the study, did not decrease nutrient solution pH in response to Fe deficiency. The more lime tolerant rootstocks, rough lemon, Cleopatra mandarin and sour orange, did decrease nutrient solution pH. But in CaSO₄ solution only sour orange increased H⁺ efflux significantly under Fe deficiency. In response to Fe deficiency, the release of phenolic compounds was increased significantly in rough lemon and Cleopatra mandarin seedlings, while the release of reducing substances was increased significantly in rough lemon, sour orange and trifoliate orange. Rough lemon was the only rootstock to respond to Fe deficiency with an increase in root-mediated reduction of chelated Fe^III at pH 6.5. At pH 8.0, both Fe-deficient rough lemon and Cleopatra mandarin roots reduced higher amounts of Fe^III from freshly precipitated Fe(OH)₃ than Fe-sufficient seedlings. Iron reduction by detached roots of Fe-deficient and Fe-sufficient rough lemon did not follow Michaelis-Menten kinetics at high substrate concentrations. Rates of Fe reduction at low substrate concentrations were inconsistent with the existence of an inducible ferric reductase in response to Fe deficiency.     

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.     

Evaluation of Sweet Orange (Citrus sinensis L. Osbeck) cv. Sathgudi Budded on Five Rootstocks for Differential Behavior in Relation to Nutrient Utilization in Alfisol

The experiment was conducted to evaluate the nutrient utilization ability of sweet orange (Citrus sinensis L. Osbeck) budded on five rootstocks (viz., Sathgudi, Rangpur lime, Cleopatra mandarin, Troyer citrange, and Trifoliate orange) in Alfisols at the experimental farm of the Citrus Improvement Project, S. V. Agricultural College Farm, Tirupati, Andhra Pradesh, India. Results of the study revealed that all the five rootstocks showed differential behaviors in terms of nutrient absorption from the soil. Rootstocks exhibited significant variation in the leaf content of potassium (K), copper (Cu), manganese (Mn), and boron (B) at all the three stages of sampling. Concentrations of the following key nutrient elements significantly varied: phosphorus (P), calcium (Ca), magnesium (Mg), zinc (Zn), and Cu at stage 1; K, Ca, Mg, Zn, iron (Fe), and Mn at stage 2; and nitrogen (N), P, Zn, Fe, and B at stage 3. The performances of rootstocks in terms of relative nutrient accumulation indices (RNAIs) were in the order of Sathgudi (1.00) > Rangpur lime (0.98) > Cleopatra mandarin (0.96) > Trifoliate orange (0.76) > Troyer citrange (0.69). The present study clearly demonstrated that citrus rootstocks employed had differential nutritional behavior and different abilities to utilize plant nutrient elements. Thus, the findings of the present study and the methodology adopted can help the horticultural breeders and nutritionists choose the best rootstock/scion combination having the desirable traits of nutrient utilization ability and also to plan effective fertilizer schedule programs for achieving greater yields.     

Effects of excess boron on growth,gas exchange,and boron status of four orange scion–rootstock combinations

Field observations indicate that boron (B)‐toxicity symptoms may occur in citrus plants from inappropriate foliar spraying or overfertilizing with B especially under low‐rainfall conditions, where B can accumulate to levels that become toxic to plant growth. Previous work has indicated that different rootstocks can greatly influence the scion's tolerance to B toxicity, however, little is known about the response of different citrus scion–rootstock combinations to excess‐B conditions. In the present study, we investigated the effects of excess B on plant growth, gas exchange, B concentration, and distribution of four scion–rootstock combinations, Newhall and Skagg's Bonanza navel orange (Citrus sinensis Osb.) scions grafted on Carrizo citrange (C. sinensis L. Osb. × Poncirus trifoliata L. Raf.) and Trifoliate orange (Poncirus trifoliata L. Raf.) rootstocks. One‐year‐old plants of the four scion–rootstock combinations were grown for 183 d in sand–perlite (1 : 1, v/v) medium under greenhouse conditions. The plants were irrigated with half‐strength Hoagland's nutrient solution containing two B concentrations, 0.25 (control) and 2.50 (excess B) mg L^–1. It was found that, apart from the combination of Newhall grafted on Carrizo citrange, the dry weights in various parts of the other three combinations were reduced by the excess‐B treatment. Furthermore, the plants of Skagg's Bonanza grafted on Carrizo citrange showed the highest growth reduction amongst the four scion–rootstock combinations. In most cases, the greater reductions in dry weight were found in roots as compared to the other plant parts under excess‐B conditions, indicating that roots were more sensitive to B toxicity than the other tissues. In the case of Newhall plants grafted on Carrizo citrange, the entire plant growth was increased by excess‐B treatment. Boron concentrations in all plants parts increased significantly by increasing the B supply in the nutrient solution. Leaves were the dominant sites of B accumulation and showed the greatest increase in B concentration compared to the other plant parts, as B concentration in the nutrient solution increased. Our results indicate that the combination of Newhall grafted on Carrizo citrange was more tolerant to B toxicity, while the combination of Skagg's Bonanza grafted on Carrizo citrange was relatively more sensitive to B toxicity, in comparison with the other scion–rootstock combinations. However, Newhall plants contained more B in leaves and in roots than Skagg's Bonanza plants when they were both grafted on Carrizo citrange, indicating that the mechanism underlying such great differential growth responses of the two scion–rootstock combinations to B toxicity may not be associated with B exclusion from roots or reduced translocation of B to shoots. Furthermore, B distribution in different plant parts implied that the mechanism was also unlikely related to altered distributions of accumulated B in plant tissues. However, inherent ability to tolerate excessive B concentration in plant tissues may be involved in B tolerance.     

不同砧木对脐橙幼树生长和叶片养分含量变化的影响

以体细胞杂种红桔+枳和红桔+粗柠檬、有性杂种Troyer枳橙和Sweingel枳柚作砧木的脐橙2年生嫁接苗为试材,利用盆栽试验研究了不同砧木对苗木生长和叶片养分含量年动态变化的影响。结果表明,红桔+枳的生长势和花量明显地优于其它砧木,红桔+粗柠檬的生长和花量介于2种有性杂种之间;砧木基本上不影响叶片N、P、K、Mg和Mn含量年变化,但明显影响叶片Ca、Fe和Zn含量的年变化;在同一个生长期,不同砧木对叶片养分含量有明显的影响。此外本文还讨论了体细胞杂种砧木的利用价值。     

The influence of different rootstocks on mineral composition of Srinagar Mandarin (citrus reticulata Blanco) leaves

In a field experiment, the influence of several rootstocks of citrus, viz., Srinagar mandarin (C. reticulta Blanco), Malta common (C. sinensis Osbeck), Jambhiri (C. lambhiri Lush), Kagzi kalan (C. aurantifolia Swingle), Rangpur lime (C. limonia Osbeck), Carrizo citrange (bigeneric hybrid), Baduvapuli (C. pennivesiculata Tanaka), Cleopatra (C. reticulata Blanco), Troyer citrange (bigeneric hybrid) and Hill lemon (C. limon Barm f.) on mineral composition of Srinagar mandarin (C. reticulata Blanco) leaves was studied. The results showed a wide and varying influence of rootstocks on mineral composition in scion leaves due to their differential ability to absorb nutrients and to translocate to scion leaves. Malta and mandarin rootstocks were generally associated with less N, Ca and Mg concentrations in scion leaves than rough lemon and citranges rootstocks. Rangpur lime followed by other mandarins resulted in relatively low P concentration whereas malta and citranges caused high P concentration as compared to other stocks. Considering the influence on K concentration, plants on malta rootstocks exhibited high level whereas it was low in plants grown on citranges.     

Salt tolerance of two lemon scions measured by leaf chloride and sodium accumulation

Effects of salinity on growth, ion content, water relationships, and chlorophyll and proline levels were measured on one‐year‐old ‘Verna’ and ‘Fino’ lemon (Citrus limon [L] Burm. F.) scions budded to either Sour orange (C. aurantium L.) or macrophylla (C. macrophylla Wester) rootstock. Trees were grown in nutrient solutions containing 2 (control), 40, or 80 mol m^‐3 NaCl for 75 days.

Growth of all combinations was reduced by salinity, but this effect was greater for both scions budded on macrophylla. Leaf chloride and sodium concentrations were lower in both scions budded on Sour orange. Leaf salt concentration was scion dependent. Leaves of ‘Fino’ lemon had higher levels of both chloride and sodium than did leaves of ‘Verna’ lemon, regardless of the rootstock considered.

Despite an accumulation of chloride and sodium in the leaves of salinized trees, leaf water potential and leaf water content increased above the control level. However, stomatal conductance declined in all rootstock/scion combinations.

Chlorophyll contents were markedly reduced by salt treatment; greater reductions were seen in ‘Fino’ lemon than in ‘Verna’ lemon on both rootstocks. Chlorophyll reductions were highly correlated with both chloride and sodium concentrations in the leaves. Free proline increased with salinity in leaves of both scions budded on Sour orange, but was unaffected on macrophylla.

Differences in the parameters determined in response to salinity were attributed to the different capacity of each specific rootstock/scion combination to import chloride and sodium into leaves.     

Irrigation water salinity affects soil nutrient distribution,root density,and leaf nutrient levels of citrus under drip fertigation 1

The purpose of this study was to determine the effects of irrigation water salinity on soil nutrient distribution, citrus leaf nutrition and root density. Irrigation water, salinized to an EC of about 0.3,1.6, or 2.5 dS/m using a 3:1 ratio of NaCl:CaCl₂ plus uniform weekly applications of liquid fertilizer, was applied through a drip system. Soil samples were taken at depths of 0–15 and 15–30 cm, both directly under the drippers and 45 cm outward from the drippers, near 8‐year old ‘Valencia’ orange trees on either Carrizo citrange or Sour orange rootstocks growing in a Candler fine sand in lysimeter tanks.

In both undisturbed and uniformly mixed soil profiles, soil pH and concentrations of Na, Ca, and P were higher under the dripper than 45 cm outward from the dripper at both depths regardless of salinity level. Soil N and Cl tended to be higher outward from the drippers than near the drippers, except in undisturbed soil at the 0–15 cm depth. Increasing salinity levels in the mixed soil profile not only increased soil EC, Na, Cl, and Ca, but also increased the concentration of P and decreased the concentration of Mg.

Root density of both rootstocks were increased by high salinity. Root densities and organic matter percentages were higher in soil sampled under drippers than that sampled outward from drippers. Leaf nutritional values and responses to salinity were dependent on rootstock as trees on sour orange had higher K and Ca, but lower Mg and Cl than trees on Carrizo. Although there were no nutrient deficiencies, K of trees on Carrizo citrange and Mg of trees on sour orange were rereduced by high salinity. An increase in leaf Ca concentrations when irrigated with salinized irrigation water likely minimized the effects of salt stress.     

缺铁胁迫柑橘砧木幼苗的光合特性和叶绿体超微结构

【目的】通过研究枳壳与枳橙砧木在缺铁和正常铁浓度处理下的反应,重点揭示两种柑橘砧木光合特性、叶绿体超微结构等对铁敏感性的差异。【方法】以柑橘的枳壳砧木和枳橙砧木实生苗为试验材料,设置缺铁 (–Fe,0 μmol/L) 和正常铁 (+Fe,37.3 μmol/L) 2个处理进行营养液培养,测定了缺铁胁迫对两种砧木苗期铁元素含量与积累量、光合色素含量、叶片糖含量的影响,并进行了叶绿体超微结构的电镜扫描。【结果】缺铁胁迫显著降低了两种砧木铁元素含量与积累量、叶片光合色素含量,且枳橙砧木光合色素含量下降幅度较大。与对照相比,缺铁后枳壳砧木叶片的糖类物质含量降低,且达到显著差异水平;而枳橙砧木叶片可溶性糖、蔗糖含量显著升高,淀粉和果糖含量显著下降。另外,缺铁胁迫条件下,两种柑橘砧木片层结构模糊,嗜饿体数目增加。并且,缺铁后枳壳砧木叶绿体长度、厚度比对照分别降低了22.1%、26.4%,枳橙砧木则分别下降了55.1%、40.4%。【结论】缺铁胁迫下,枳橙砧木幼苗的铁元素含量和积累量、叶片光合色素含量、叶绿体超微结构等均比枳壳砧木受到较大影响,表明枳橙砧木比枳壳砧木对铁营养缺乏更加敏感。     

Humic Acid–Like Substances Extracted from Compost Improve Fe Nutrition of Lemon Grown on Calcareous Soil: An Environmentally Safe Approach

The short-term effectiveness of soil-applied humic acid–like substances [naturally complexed or uncomplexed with iron (Fe)] extracted from composted poultry (HLSP) and sheep (HLSS) manures in preventing lime-induced Fe chlorosis in Eureka lemon (Citrus lemon L.) cuttings grafted on sour orange (Citrus aurantium L.) was investigated and compared with the commonly applied ethylenediamine di-2-hydroxyphenyl acetate ferric (FeEDDHA). Treatments were untreated plants and plants fertilized with FeEDDHA, HLSP, and HLSS injected into the soil at a total rate of 25 mg Fe per plant each. Chlorophyll concentration index (CCI) of the youngest fully expanded leaves, growth vigor, and leaf Fe concentration were measured. HLSP and HLSS, similar to FeEDDHA, resulted in significantly greater CCI values, growth vigor, and leaf Fe concentration compared to untreated plants. HLSP and HLSS offer potential alternative to FeEDDHA to prevent lime-induced Fe deficiency in Eureka lemon. Concentrates of HLSP and HLSS can be commercially prepared to offer an inexpensive and environmentally safe product.     

Estimation of preliminary reference values for macro and micronutrients in ‘Valencia’ orange in Venezuela,by means of the compositional nutrient diagnosis system

The present study was aimed at developing preliminary reference values for foliar tissue for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) for `Valencia´ orange in Venezuela, using the Compositional Nutrient Diagnosis system (CND). References values were derived from a database comprising the nutrients concentrations and the yields of `Valencia´ orange trees (Citrus sinensis L. Osbeck) grafted on two different rootstocks, viz., Volkamer lemon (Citrus volkameriana Pasq.), and Cleopatra tangerine (Citrus reshni, Hort. ex. Tan). Cutoff values separating high- and low-yield sub-samples were estimated through modeling the cumulative variance ratio function versus yield relationships with the Boltzmann equation. For macronutrients, the norms developed were dependent upon the inclusion of the micronutrients concentrations in the calculations, and on the rootstocks. Care must thus be exercised, since nutrient indexes, and thus nutritional diagnosis, are based upon proper selection of such values.     

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

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.     

Effect of the iron supply on the nutrition of different citrus variety/rootstock combinations using dris 1

The Diagnosis and Recommendation Integrated System (DRIS) has been found reliable in diagnosing nutrient requirements, despite changes in the tissue sampling or the time sampling. Relatively few researchers use the results obtained by hydroponic culture to make a DRIS data bank. In this work, results obtained in this way have been utilized as DRIS reference values to evaluate the iron (Fe) supply influence on the nutrition of different citrus combinations under normal and deficient Fe conditions. The DRIS indices have been compared with standard methods to evaluate the effectiveness of this system of interpretation. The Citrus macrophylla rootstock for lemons is more resistant to Fe chlorosis than Sour orange. Based on the diagnosis of visual symptoms, the Citrus volkameriana is more resistant to this nutritional deficiency for oranges than the Cleopatra mandarin.     

Effectiveness of Vivianite to Prevent Lime-Induced Iron Deficiency in Lemon Trees Grown on Highly Calcareous Soil

The short-term effectiveness of three application rates of vivianite [(Fe₃(PO₄)₂·8H₂O)] in preventing lime-induced iron (Fe) chlorosis in Eureka lemon (Citrus lemon L.) cuttings grafted on sour orange (Citrus aurantium L.) was investigated and compared with the commonly applied iron ethylenediaminedi(o-hydroxyphenylacetic) acid (FeEDDHA). Treatments were suspension of vivianite injected into the soil at three rates (0.5, 1.0, and 2.0 g kg^?1 soil), 417 mg FeEDDHA per plant, and untreated plants. Chlorophyll concentration index (CCI) of the youngest fully expanded leaves was estimated. Growth vigor and leaf Fe concentration were also measured. Vivianite, particularly at the greatest two rates, resulted in significantly greater growth vigor and leaf Fe concentration and exhibited greater CCI values compared to untreated plants similar to FeEDDHA. However, if excessive growth vigor is not favorable, the 0.5 g vivianite kg^?1 soil is recommended for farmers. Vivianite is a potential environmentally safe alternative to the expensive FeEDDHA to prevent Fe chlorosis in lemon.     

Comparative study on the effectiveness of several iron compounds in the iron chlorosis correction in citrus plants

A comparative study was carried out on the effectiveness of several commercial Fe‐compounds applied through the soil as well as via leaf spray, with a view to control the Fe‐chlorosis in Verna lemon trees directly grafted on sour orange rootstock, with a Salustiano orange tree as intermediate. The results obtained during 1985 confirm the conclusions of previous experiments: The most effective treatments were the leaf spray with Fe‐polyflavonoids, though it is interesting that Fe‐chelates applied to soil were also highly effective, as Fe leaf levels were higher than 100 ppm one month after treatments.     

Differential response of citrus rootstocks to aluminum levels in nutrient solutions: I. plant growth 2

The objectives of this study were to determine and compare the Al tolerance of selected citrus rootstocks. Six‐month‐old seedlings of five citrus rootstocks were grown for 60 days in nutrient solutions. The solutions contained 7 levels of Al ranging from 4 to 1655 μM and similar P concentration of 28 μM. The nutrient solution pH was maintained at 4.0±0.1 and the temperature at 25±1°C. At high Al treatment levels, plants had thickened root tips and root caps covered with black gelatinous material. At high levels of Al treatments, seedlings of some rootstocks had yellow, mottled, and withered new leaves near end of experiment. New‐growth root lengths and shoot height responded differently to Al concentrations in the nutrient solution. New‐growth fresh weight of whole plants appeared to be the most sensitive indicator of Al tolerance. Based on response of fresh weight of whole plants to Al concentrations, relative Al tolerances of the rootstocks were Cleopatra mandarin > rough lemon > sour orange > Swingle citramelo > Carrizo citrange. The neutral or dividing Al concentrations in solution between beneficial and toxic effects were 371, 193, 189, 178, and < 100 μM Al, respectively, for the above rootstocks. Concentrations below or above the neutral Al levels caused either beneficial or toxic effects, respectively. The apparent optimum Al concentrations for the growth of whole plants were 163, 93, 89, 85, and <50 μM, respectively.