Influence of Rootstock Genotype and Ploidy Level on Common Clementine (Citrus clementina Hort. ex Tan) Tolerance to Nutrient Deficiency

Abstract

Nutrient deficiency, in particular when this involves a major macronutrient (N, P, and K), is a limiting factor on the performance of plants in their natural habitat and agricultural environment. In the citrus industry, one of the eco-friendliest techniques for improving tolerance to biotic and abiotic stress is based on the grafting of a rootstock and a scion of economic interest. Scion tolerance may be improved by a tetraploid rootstock. The purpose of this study was to highlight if tolerance of a common clementine scion (C) (Citrus clementina Hort. ex Tan) to nutrient deficiency could be improved by several diploid (2×) and their tetraploid (4×) counterparts citrus genotypes commonly used as rootstocks: Trifoliate orange × Cleopatra mandarin (C/PMC2x and C/PMC4x), Carrizo citrange (C/CC2x and C/CC4x), Citrumelo 4475 (C/CM2x and C/CM4x). The allotetraploid FlhorAG1 (C/FL4x) was also included in the experimental design. The impact of nutrient deficiency on these seven scion/rootstock combinations was evaluated at root and leaf levels by investigating anatomical parameters, photosynthetic properties and oxidative and antioxidant metabolism. Nutrient deficiency affects foliar tissues, physiological parameters and oxidative metabolism in leaves and roots in different ways depending on the rootstock genotype and ploidy level. The best known nutrient deficiency-tolerant common clementine scions were grafted with the doubled diploid Citrumelo 4475 (C/CM4x) and the allotetraploid FlhorAG1 (C/FL4x). These combinations were found to have less foliar damage, fewer changes of photosynthetic processes [leaf net photosynthetic rate (P _net ), stomatal conductance (g _s ), transpiration (E), maximum quantum efficiency of PSII (F _v /F _m ), electron transport rate (ETR), ETR/P _net ], and effective quantum yield of PSII [Y(II)], less malondialdehyde accumulation in leaves and better functional enzymatic and non-enzymatic antioxidant systems. Common clementine scions grafted on other 4× rootstocks did not show better tolerance than those grafted on their 2× counterparts. Chromosome doubling of rootstocks did not systematically improve the tolerance of the common clementine scion to nutrient deficiency.

Keywords: Citrus; antioxidant; grafting; nutrient deficiency; oxidative stress; photosynthesis; polyploidy.

FIGURE 1

Assessment of leaf damages after 210 days of total nutrient deficiency (0%) on clementine trees grafted onto the seven rootstocks compared to controls (100%). Genotypes are ranked based on the leaf symptoms from the lesser affected (1) to the more affected (3).

FIGURE 2

Hierarchical cluster analysis and heatmap displaying mineral contents and parameters responding to nutrient deficiency in different scion/rootstock combinations after 210 days of nutrient deficiency (D210) (A) and after 30 days of recovery (30DR) (B). Values are means of 3 independent (n = 3) measurements for each parameter. Hierarchical cluster analysis dispatches the seven scion/rootstock combinations based on the different parameters. The heatmap shows the differences between the seven scion/rootstock combinations and treatments for each parameter. Color scale shows the intensity of the normalized mean values of different parameters. Values are associated with color ranging from yellow (low) to dark green (high).