Nutrient Deficiency Tolerance in Citrus Is Dependent on Genotype or Ploidy Level

Abstract

Plants require essential minerals for their growth and development that are mainly acquired from soil by their roots. Nutrient deficiency is an environmental stress that can seriously affect fruit production and quality. In citrus crops, rootstock/scion combinations are frequently employed to enhance tolerance to various abiotic stresses. These tolerances can be improved in doubled diploid genotypes. The aim of this work was to compare the impact of nutrient deficiency on the physiological and biochemical response of diploid (2x) and doubled diploid (4x) citrus seedlings: Volkamer lemon, Trifoliate orange × Cleopatra mandarin hybrid, Carrizo citrange, Citrumelo 4475. Flhorag1 (Poncirus trifoliata + and willow leaf mandarin), an allotetraploid somatic hybrid, was also included in this study. Our results showed that depending on the genotype, macronutrient and micronutrient deficiency affected certain physiological traits and oxidative metabolism differently. Tetraploid genotypes, mainly Flhorag1 and Citrumelo 4475, appeared resistant compared to the other genotypes as indicated by the lesser decrease in photosynthetic parameters (P _net, F _v/F _m, and G _s) and the lower accumulation of oxidative markers (MDA and H₂O₂) in roots and leaves, especially after long-term nutrient deficiency. Their higher tolerance to nutrient deficiency could be explained by better activation of their antioxidant system. For the other genotypes, tetraploidization did not induce greater tolerance to nutrient deficiency.

Keywords: antioxidant; citrus; nutrient deficiency; oxidative stress; photosynthesis; polyploid.

FIGURE 1

Leaf damages after 210 days of total nutrient deficiency on the nine genotypes (0%) compared to controls (100%). Genotypes are ranked based on the leaf symptoms from the unaffected (0) to the more affected (3).

FIGURE 2

Evolution of net photosynthesis rate (P_net), stomatal conductance (G_s) and chlrorophyll fluorescence ratio (F_v/F_m), throughout the nutrient deficiency in leaves of 2x and 4x seedlings. The white and black bars correspond to the values obtained from 2x and 4x seedlings, respectively.(Concentrations were measured after different period of nutrient deficiency: days 0 (D0) for the control, 70 (D70), 140 (D140) and 210 (D210) and after 30 days of recovery (30DR). The results obtained are expressed as ratios with respect to the values obtained on control leaves which have not been subjected to stress. The results are presented as mean (± standard error) of nine independent measurements (n = 9). Data were analyzed using ANOVA and Fisher LSD tests (P < 0.05). Distinct capital letter indicate significant differences between all diploid seedlings at a point of the time course. Different lower case letters indicate significant value change along the time course for in 2x seedlings. For 4x seedlings, the same procedure has been followed and the results are indicated in bold roman. An asterisk indicates significant differences between 2x and 4x seedlings of the same variety at a point of the time course.)

FIGURE 3

Evolution of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentration, throughout the nutrient deficiency in leaves and roots of 2x and 4x genotypes. The white and black bars correspond to the values obtained from 2x and 4x genotypes, respectively. Concentrations were measured after different period of nutrient deficiency in: days 0 (D0) for the control, 70 (D70), 140 (D140) and 210 (D210) and after 30 days of recovery (30DR) in leaves and days 0 (D0) for the control, 70 (D70) and 210 (D210) and after 30 days of recovery (30DR) in roots. The results obtained are expressed as ratios with respect to the values obtained, respectively, on control leaves and control roots which have not been subjected to stress. The results are presented as mean (± standard error) of three independent measurements (n = 3). Data were analyzed using ANOVA and Fisher LSD tests (P < 0.05). Distinct capital letter indicate significant differences between all 2x genotypes at a point of the time course. Different lower case letters indicate significant value change along the time course for one 2x genotype. For 4x genotypes, the same procedure has been followed and the results are indicated in bold roman. An asterisk indicates significant differences between 2x and 4x genotypes of the same variety at a point of the time course.

FIGURE 4

Biplot obtained from PCA performed after (A,B) 210 days of total nutrient deficiency and 30 days of recovery (C,D) in leaves of the nine genotypes. (A,C) dispersion of genotypes and (B,D) contribution of the variables to the dispersion. The variables analyzed are net photosynthesis rate (P_net), stomatal conductance (G_s), chlorophyll fluorescence (F_v/F_m), malondialdehyde (MDA), hydrogen peroxide (H₂O₂), antioxidant enzymes (SOD, CAT, APX, and DHAR), reduced ascorbate (Asa), oxidized ascorbate (DHA), total ascorbate (tAsa), ascorbate redox status (Asa/DHA), and proline.