Nutritional Performance of Five Citrus Rootstocks under Different Fe Levels

Abstract

Iron is an essential micronutrient for citrus, playing an important role in photosynthesis and yield. The aim of this paper was to evaluate the tolerance to Fe deficiency of five citrus rootstocks: sour orange (S), Carrizo citrange (C), Citrus macrophylla (M), Troyer citrange (T), and Volkamer lemon (V). Plants were grown for 5 weeks in nutrient solution that contained the following Fe concentrations (in µM): 0, 5, 10, 15, and 20. At the end of the experiment, biomass (dry weight-DW), leaf area, total leaf chlorophyll (CHL), and the activity of root chelate reductase (FCR) were recorded. Additionally, the mineral composition of roots (R) and shoots (S) was evaluated. Principal component analysis was used to study the relationships between all parameters and, subsequently, the relations between rootstocks. In the first component, N-S, P-S, Ca-S, Cu-S, Zn-S, Mn-S, Zn-R, and Mn-R concentrations were related to leaf CHL and FCR. Increases in leaf CHL, Mg-R, and DW (shoots and roots) were inversely related to Cu-R, which was shown in the second component. The values obtained were consistent for V10, C15, and C20, but in contrast for S0 and S5. In conclusion, micronutrient homeostasis in roots and shoots of all rootstocks were affected by Fe stress conditions. The Fe/Cu ratio was significantly related to CHL, which may be used to assist rootstock performance.

Keywords: Fe chlorosis; citrus; ferric chelate reductase; mineral composition.

Figure 1

(a) Principal component analysis of nutrient concentrations (in mg g⁻¹ DW: N, P, K, Ca, and Mg; in µg g⁻¹: DW: Fe, Cu, Zn, and Mn) in shoots (S) and roots (R) of five citrus rootstocks. PC1—first principal component; PC2—second principal component. Each vector represents the loadings of variables (nutrients and Fe chlorosis parameters: CHL, leaf area, S-DW, R-DW, and FCR) in each principal component. Loadings represent the relative contribution of each nutrient to that component. Concentration of nutrients in shoots (S) and roots (R): N (N-S and N-R), P (P-S and P-R), K (K-S and K-R), Ca (Ca-S and Ca-R), Mg (Mg-S and Mg-R), Cu (Cu-S and Cu-R), Fe (Fe-S and Fe-R), Mn (Mn-S and Mn-R), and Zn (Zn-S and Zn-R). (b) Projection of 25 scores resulting from 5 rootstocks (S —sour orange, V—Volkamer lemon, T—Toyer citrange, C—Carrizo citrange and M—C. macrophylla) × 5 Fe levels (0, 5, 10, 15, and 20 µM of Fe) onto the plane defined by the principal components. The labels of treatments result from the combination of the letter associated with each rootstock and the concentration of Fe in nutrient solution.

Figure 2

(a) Principal component analysis of nutrient contents (in mg: N, P, K, Ca, and Mg; and in µg: Fe, Cu, Zn, and Mn) of five citrus rootstocks considering the total in plants (roots plus shoots). PC1—first principal component; PC2—second principal component. Each vector represents the loadings of variables (nutrients and Fe chlorosis parameters: CHL, leaf area, S-DW, R-DW, and FCR) in each principal component. Loadings represent the relative contribution of each nutrient to that component. (b) Projection of 5 Fe levels (0, 5, 10, 15, and 20 µM of Fe) considering all rootstocks.

Figure 3

Linear regression relationships between total leaf CHL (µmol m⁻²) and total Fe/Cu ratio for each rootstock (circles) and considering all treatments together (purple line). Treatments are 5 rootstocks (S—sour orange, V—Volkamer lemon, T—Toyer citrange, C—Carrizo citrange and M—C. macrophylla) × 5 Fe levels (0, 5, 10, 15, and 20 µM of Fe). The coefficient of determination (R²) is presented for each model and significant models (p < 0.05) are indicated by one asterisk (*).