Mongi Zekri

Salinity tolerance of citrus rootstocks: Effects of salt on root and leaf mineral concentrations

The effects of three concentrations of sodium chloride (NaCl) on seven citrus rootstocks were studied under greenhouse conditions. Leaf and root mineral concentrations and seedling growth were measured. Sodium chloride was added to the nutrient solution to achieve final osmotic potentials of −0.10, −0.20, and −0.35 MPa. Increasing the concentration of NaCl in the nutrition solution reduced growth proportionally and altered leaf and root mineral concentrations of all rootstocks. Significant differences in leaf and root mineral concentration among rootstocks were also found under stressed and non-stressed conditions. Salinity caused the greatest growth reduction in Milam lemon and trifoliate orange and the least reduction in sour orange and Cleopatra mandarin. No specific nutrient deficiency was the sole factor reducing growth and causing injury to citrus rootstocks. Sodium chloride sensitivity of citrus rootstocks in terms of leaf burn symptoms and growth reduction could be attributed more to Cl than to Na. Sodium and Cl concentrations were greater in the leaves than in the roots, particularly at the medium and high salinity levels. Root Cl was not useful for assessing injury because no differences were found in root Cl concentrations among rootstocks. Increasing salinity level did not affect the level of N and Ca in the roots but did reduce N and Ca levels in the leaves. No relationship in mineral concentration or accumulation seemed to exist between citrus leaves and roots. At the −0.10 MPa salinity level, sour orange, rough lemon, and Milam were not able to exclude either Na or Cl from their leaves. Trifoliate orange and its two hybrids (Swingle citrumelo and Carrizo citrange) excluded Na at the lowest salt level used, but were unable to exclude Na at the higher salinity levels. Similarly, Cleopatra mandarin excluded Cl at the lowest salt level, but was not able to exclude Cl at higher salt concentrations. Hence, the ability of citrus rootstocks to exclude Na or Cl breaks down at higher salt concentrations.

Effects of NaCl on growth and physiology of sour orange and Cleopatra mandarin seedlings

Abstract The responses of sour orange (SO) and Cleopatra mandarin (CM) to salt stress were studied because of the difference in their ability to accumulate Cl in the leaves. Seedlings of these two citrus rootstocks were grown in fine sand under greenhouse conditions. Salinity treatments were initiated by adding NaCl to half-strength Hoaglands solution to achieve final osmotic potentials of −0.10, −0.20, and −0.35 MPa. The no-salt control treatment had an osmotic potential of −0.05 MPa. Seedlings were harvested 6 months after starting NaCl treatments. No significant differences in growth, root hydraulic conductivity (RC), stomatal conductance, and evapotranspiration were detected between SO and CM. However, all these variables were significantly reduced by NaCl. At a relatively low salinity level (−0.10 MPa), shoot and root dry weights, stem cross-sectional area, total leaf area, and fibrous root length were reduced by 44–55%. With all treatments, a positive linear relationship was found between RC and stomatal conductance. Significant differences between SO and CM were found in leaf succulence, specific leaf weight (SLW), Cl accumulation, and leaf chlorophyll content. Sour orange seedlings accumulated higher amounts of Cl and had higher SLW and succulence but lower chlorophyll than CM seedlings. At the first salinity level, chlorophyll was reduced by 56% in SO but only by 11% in CM. The different responses to salt stress between the two rootstocks were mainly attributed to the known failure of SO to exclude Cl even at relatively low salinity levels.

Treated municipal wastewater for citrus irrigation 1

Abstract Treated, reclaimed municipal wastewater was evaluated on citrus trees in central Florida for over six years. The effects of irrigation with reclaimed wastewater on soil water content, soil chemical analysis, leaf mineral status, and fruit quality were compared with those of irrigation with well water. Irrigation with reclaimed water increased mineral residues in the soil profile, altered leaf mineral concentration and fruit quality, and promoted better tree performance and more weed growth relative to irrigation with well water. Higher accumulation of nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) in soils irrigated with reclaimed water were not significantly reflected in leaf mineral status. Although leaf sodium (Na), chloride (Cl), and boron (B) concentrations were noticeably higher in reclaimed water treatments than in those of well water, they are still far below the toxicity levels. This highly treated wastewater in central Florida has been found to be a very safe and good opt...

Comparative effects of NaCl and polyethylene glycol on root distribution, growth, and stomatal conductance of sour orange seedlings

An experiment was conducted to study sour orange (Citrus aurantium L.) seedling root density, distribution, and morphological development under NaCl and polyethylene glycol (PEG) stresses in relation to shoot growth and stomatal conductance. Plants were treated with 2 stress levels (− 0.12 and − 0.24 MPa) of NaCl and PEG 4000 for 7 months. Root observation chambers were used to monitor root growth and distribution under stressed and non-stressed conditions. Seedlings receiving NaCl or PEG treatments produced fewer roots and shallower root systems with 46 to 65% of the roots occurring in the top portion of the soil. Fibrous root weight per unit length was increased by 24 to 30% by PEG but was not significantly increased by NaCl.Root growth rate usually alternated with shoot growth in a 2-month cycle. This alternating pattern was not shifted by NaCl and PEG stresses. In all NaCl and PEG treatments, growth was depressed and stomatal conductance was reduced. Compared to controls, plants that received NaCl or PEG had smaller shoot and root dry weights, fewer leaves, shorter height, and fewer roots. Sodium chloride usually caused less damage than PEG to sour orange seedlings suggesting that NaCl and PEG acted through different mechanisms.

Seedling emergence, growth, and mineral concentration of three citrus rootstocks under salt stress

Abstract Salt tolerance of Carrizo citrange (CC), sour orange (SO), and Cleopatra mandarin (CM) rootstocks during emergence and early seedling stage of development was studied under greenhouse conditions. Increasing salt concentration in the nutrient solution delayed and depressed seedling emergence (SE), increased time to 50% emergence, reduced seedling growth (SD) but did not affect emergence spread. At the first salinity level (5 mmol), emergence of the first seedling (EFS) was delayed by 2–3 days in CC and one day in SO but was not affected in CM. At the two lowest salinity levels (5 and 10 mmol), final percent emergence (FPE) was not affected in CC but was reduced in SO and CM while shoot biomass was reduced in CC but was not affected in SO and CM. This study showed a non‐consistent trend among citrus rootstocks concerning whether the delay in emergence is more sensitive to salt stress than final percent emergence. However, SG was generally more affected by salinity than SE, particularly at high sali...

Use of controlled-release fertilizers for young citrus trees☆

Abstract The effects of several controlled-release fertilizer compounds were compared with those of a soluble fertilizer mixture on young citrus trees growing in sandy soils under a subtropical environment. Soluble fertilizers were found to be more readily available and had shorter residual effects on leaf and soil N and K than controlled-release fertilizers. The high rate Osmocote (Sierra) treatment gave the highest leaf Mg content in 1988, probably because MgO was included in Osmocote, while MgSO4 was used in the other fertilizer formulations. In 1988, Osmocote treatments gave the highest leaf Fe concentrations, which could be attributed to the high Fe content in the Osmocote fertilizer. No difference in tree growth was found among soluble and controlled-release fertilizer treatments. Soluble fertilizers produced smaller size fruit and yielded less fruit than controlled-release fertilizers, but the differences in fruit yield were not significant. The lack of significance in fruit yield and in most fruit quality parameters between the soluble and controlled-release fertilizer treatments could be attributed to the highly variable data because it was the first fruit crop. Controlled-release fertilizers were very promising for sandy soils and subtropical environments as they can be applied in smaller amounts and less often than soluble fertilizers, without adverse effects on tree growth or fruit production and quality.

Effects of PEG-induced water stress on two citrus cultivars

Abstract The effect of polyethylene glycol (PEG) 4000 on sour orange (SO) and Cleopatra mandarin (CM) rootstock seedlings grown in fine sand under greenhouse conditions was studied. The PEG treatments were initiated by adding PEG to half strength Hoaglands solution to achieve final osmotic potentials of ‐0.10, ‐0.20, and ‐0.35 MPa. The no PEG control treatment had an osmotic potential of ‐0.05 MPa. Seedlings were harvested 6 months after starting PEG treatments. No significant differences in growth, root hydaulic conductivity, water flow rate, stomatal conductance, and evapotranspiration were detected between SO and CM. However, all these variables were significantly reduced by PEG. At a relatively low PEG level (‐0.10 MPa), shoot and root dry weights, stem cross sectional area, total leaf area, and fibrous root length were reduced by more than 60%. Although SO and CM were similarly sensitive to PEG‐induced water stress, significant differences between these two rootstocks were found in leaf mineral comp...

Application of micronutrients to citrus trees through microirrigation systems

Abstract Using conventional soil and foliar spray applications to correct micronutrient deficiency in citrus has not been completely satisfactory. Therefore, this study was developed to test the effectiveness of micronutrient application through microirrigation (fertigation) at rates similar to those recommended for foliar spray application. Three field experiments were conducted on ‘Valencia’ orange [Citrus sinensis (L.) Osb.] trees to study the absorption of Fe, Mn, Zn, and Cu by periodically analyzing leaf samples. The effectiveness of fertigation with micronutriems was found to depend on the fertilizer source. Application of chelated Fe, Mn, and Zn through irrigation systems increased the concentrations of these micronutrients in the leaves. The nitrate forms of Fe, Mn, and Zn were ineffective, as was the sulfate form of Zn. The sulfate form of Mn was occasionally effective, but the sulfate form of Cu was very effective. The application of chelated micronutrients through fertigation shows promise in c...

PEG stress altered citrus root and leaf mineral concentrations

Abstract An experiment was conducted to study the effects of polyethylene glycol (PEG) on citrus growth and mineral composition. Seedlings of 7 citrus rootstock cultivars were treated with three osmotic potential levels (‐0.10, ‐0.20, and ‐0.35 MPa) of PEG for five months under greenhouse conditions. Increasing the concentration of PEG in the nutrient solution proportionally reduced root and shoot growth in all rootstocks. Although roots were in direct contact with PEG, their growth was less affected by PEG treatments than that of shoots. Seedling growth was reduced the most in Carrizo citrange and Milam lemon. Significant differences in root and leaf mineral concentrations among cultivars were found under PEG stressed and non stressed conditions. Furthermore, no consistent relationship in mineral absorption, translocation and accumulation seemed to exist between citrus roots and leaves. Root and leaf mineral concentrations were also significantly altered by PEG in all rootstock cultivars. Nitrogen (N), p...

Osmotic and toxic ion effects on seedling emergence and nutrition of citrus rootstocks

Abstract The effects of isosmotic solutions of sodium chloride (NaCl), polyethylene glycol (PEG), and mannitol with or without supplemental calcium (Ca) were compared to separate osmotic effects from toxic ion effects of salts on seed imbibition, seedling emergence, and the early stage of seedling growth of three citrus rootstocks. The rate of seed imbibition was relatively low for sour orange (SO) in PEG treatments which caused a delay in seedling emergence. These results of PEG supported earlier findings which suggested the existence of a critical level of hydration that seeds must reach before germination can proceed. Final percent emergence (FPE) was reduced the most by NaCl and mannitol compared with PEG. Furthermore, Ca addition to mannitol and NaCl solutions improved FPE in Cleopatra mandarin (CM) and trifoliate orange (TO). These results demonstrated that the effects of mannitol and NaCl on FPE went beyond the osmotic effects. Seedling growth was reduced the most by mannitol not only due to its up...