Vicente Gimeno

The tolerance of Jatropha curcas seedlings to NaCl: An ecophysiological analysis

Jatropha curcas L. is a biodiesel crop that is resistant to drought stress. However, the salt tolerance of this plant has not yet been studied. To address this question, J. curcas seedlings were grown in a fertilised substrate to evaluate the effects of salinity stress on growth, leaf water relation and organic solutes, leaf and root mineral concentrations, chlorophyll fluorescence parameters, and carbohydrate concentration. The experiment consisted of six treatments with different concentrations of NaCl in the irrigation water: 0 (control), 30, 60, 90, 120 and 150 mM. The total biomass exhibited a salt-induced decrease in the 60 mM or higher NaCl concentrations. The Cl(r) concentration was higher than the Na(+) concentration in all of the plant tissues. The water potential and relative water content of the leaves were not affected by any of the salt treatments. However, salinity induced a decline in the leaf K(+) concentration, together with a significant enhancement in the leaf P, S, Fe, Zn, Mn and Cu levels. The net assimilation of CO₂ also decreased with the salt treatment, due in part to non-stomatal limitation from the increase in C(a)/C(i) and a decrease in the maximum quantum efficiency (F(v)/F(m)) of photosystem II and soil plant analysis development (SPAD) units. This work suggests that J. curcas seedlings exhibit a moderate tolerance to salinity, as the plants were able to tolerate up to 4 dS m(-1) (EC water irrigation; 30 mM NaCl). The negative influences of salinity in this crop are mainly due to Cl(r) and/or Na(+) toxicity and to a nutritional imbalance caused by an increase in the Na(+)/K(+) ratio. The osmotic effect of salinity in this species is negligible, perhaps due to its strong control of leaf transpiration, which reduces water loss.

GROWTH AND MINERAL NUTRITION ARE AFFECTED BY SUBSTRATE TYPE AND SALT STRESS IN SEEDLINGS OF TWO CONTRASTING CITRUS ROOTSTOCKS

We evaluated plant growth and leaf and root mineral nutrient responses to salinity of two-month-old citrus rootstock seedlings growing in four types of container growth media: aerated hydroponic solution, river washed sand, perlite, or a native clay-loam soil. Seedlings of Cleopatra mandarin (Citrus reticulata Blanco; Cleo, relatively salt tolerant) and Carrizo citrange [C. sinensis (L.) Osb. Poncirus trifoliate L.; Carr, salt sensitive] were grown in a controlled-environment chamber using Hoaglands nutrient solution containing either 0 mM (Control) or 50 mM sodium chloride (NaCl; salt). Without salt, seedlings in solution culture and sand grew the most and seedlings in perlite and clay-loam grew the least. The salinity treatment decreased growth in both Cleo and Carr seedlings in solution and sand but not in smaller seedlings in perlite and clay-loam soil. Cleo seedlings had lower leaf chloride (Cl−) concentration and higher leaf sodium (Na+) concentration than Carr seedlings. In the salinized clay-loam soil, Cl− and Na+ concentrations tended to be highest in leaves but lowest in roots. Salt treatment generally reduced leaf calcium (Ca2+) concentration in Cleo seedlings in all substrates and in Carr seedlings in solution and perlite. Based on total plant dry weight, seedlings grown in solution culture and sand were more salt tolerant than those grown in perlite and clay-loam soil. Since the reduced growth in clay-loam soil and perlite negated the effects of the salt treatment, salt tolerance was not linked to leaf Cl− concentration.

Orange varieties as interstocks increase the salt tolerance of lemon trees

Summary We investigated the ability of interstocks to increase salt tolerance in lemon trees. We compared 2-year-old ‘Verna’ lemon trees [Citrus limon (L.) Burm.; VL] grafted on Sour Orange (C. aurantium L.; SO) rootstock either without an interstock (VL/SO), or interstocked with ‘Valencia’ orange (C. sinensis Osbeck; VL/V/SO), or with ‘Castellano’ orange (C. sinensis Osbeck; VL/C/SO). Trees were grown under greenhouse conditions and supplied with nutrient solutions containing 0, 30, or 60 mM NaCl. Reductions in leaf growth caused by salt treatment were greatest in non-interstocked (VL/SO) trees, followed by VL/C/SO trees, and were the least in VL/V/SO trees. Although the levels of Cl− and Na+ ions in the roots and stems were not affected by either interstock, leaf concentrations of Cl− and Na+ were higher in VL/SO trees than in VL/C/SO or VL/V/SO trees, suggesting that an interstock in Citrus trees could limit the uptake and transport of such ions to the shoots. Saline-treated VL/SO trees also tended to have the lowest shoot:root (S:R) ratios; so, overall, there was a negative relationship between S:R ratio and leaf Cl- ion concentration. Leaf transpiration (Eleaf) may also be involved in the reduction in leaf Cl− concentration, as interstocked trees had lower Eleaf values at mid-day than non-interstocked trees. Salinity increased leaf concentrations of Ca2+ in VL/C/SO trees and increased both leaf K+ and N concentrations in all trees, regardless of interstock. Salinity reduced leaf water potentials and osmotic potentials, such that leaf turgor was increased in all trees.

Rapid estimation of nutritional elements on citrus leaves by near infrared reflectance spectroscopy

Sufficient nutrient application is one of the most important factors in producing quality citrus fruits. One of the main guides in planning citrus fertilizer programs is by directly monitoring the plant nutrient content. However, this requires analysis of a large number of leaf samples using expensive and time-consuming chemical techniques. Over the last 5 years, it has been demonstrated that it is possible to quantitatively estimate certain nutritional elements in citrus leaves by using the spectral reflectance values, obtained by using near infrared reflectance spectroscopy (NIRS). This technique is rapid, non-destructive, cost-effective and environmentally friendly. Therefore, the estimation of macro and micronutrients in citrus leaves by this method would be beneficial in identifying the mineral status of the trees. However, to be used effectively NIRS must be evaluated against the standard techniques across different cultivars. In this study, NIRS spectral analysis, and subsequent nutrient estimations for N, K, Ca, Mg, B, Fe, Cu, Mn, and Zn concentration, were performed using 217 leaf samples from different citrus trees species. Partial least square regression and different pre-processing signal treatments were used to generate the best estimation against the current best practice techniques. It was verified a high proficiency in the estimation of N (Rv = 0.99) and Ca (Rv = 0.98) as well as achieving acceptable estimation for K, Mg, Fe, and Zn. However, no successful calibrations were obtained for the estimation of B, Cu, and Mn.