Characterization of Citrus Rootstock Under Conditions of Boron Toxicity

Boron (B) is an essential element for an adequate development of citrus orchards. However, citrus trees are vulnerable to high B concentrations, generating morphological and physiological alterations incompatible with the proper production of citrus. In this sense, citrus rootstocks can provide valuable capabilities to citrus trees including tolerance to different stresses. The objective of this work is the characterization of 2247 x 6070-02-2 citrus rootstock using as a reference Carrizo citrange rootstock under B toxicity conditions (2.5 mM boric acid). Carrizo citrange is a diploid hybrid, and 2247 x 6070-02-2 is a novel low-HLB-sensitive tetraploid. B excess effects were analyzed after four weeks of treatment using 0.05 (control) and 2.5 mM (toxicity) H3BO3 concentrations, respectively, in hydroponic growth conditions. The characterization of 2247 x 6070-02-2 rootstock compared to Carrizo citrange was performed by measuring physiological parameters in leaves related to photosynthesis, stress oxidative responses, B content, and gene expression. The lower transpiration rate and, especially, the higher expression of the CsXIP1;1 gene and the better antioxidant defense mechanisms shown by 2247 x 6070-02-2 make this rootstock more tolerant to high B content than Carrizo citrange.