Incidence of Rio Grande Gummosis of Grapefruit Is Not Associated with Concentrations of Anions in Soil Water

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  • 1 University of Florida, Institute of Food and Agricultural Sciences, Tropical Research and Education Center, 18905 SW 280 Street, Homestead, FL 33031
  • | 2 University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850
  • | 3 University of Florida, Institute of Food and Agricultural Sciences, Indian River Research and Education Center, 2199 South Rock Road, Fort Pierce, FL 34945

The objective of this study was to evaluate the role of chloride (Cl-) and other anions in soil water on the incidence and severity of Rio Grande Gummosis (RGG) in grapefruit (Citrus paradisi MacFadyen) trees. White `Marsh' grapefruit trees on sour orange (C. aurantium Lush.) rootstock were grown on two-row raised beds. Due to differential rates of K application (as KCl), the trees received various rates of Cl- ranging from 0 to 156 kg·ha-1 per year. Soil water was sampled using suction lysimeters at 120- and 180-cm depths. The severity of RGG was evaluated 18 months following the application of various rates of KCl. The concentration of Cl- in soil water samples varied from 16.2 to 617 mg·L-1, with mean concentrations across all treatments of 160.7 and 188.4 mg·L-1 for 120- and 180-cm depth water samples, respectively. The concentrations of Cl- and other anions (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{PO}_{4}^{3-}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{SO}_{4}^{2-}\) \end{document}) in soil water at either 120- or 180-cm depth were poorly related to the incidence or severity of RGG (R = -0.10 to -0.28). Chloride concentrations in the soil water ranged from 20 to 617 mg·L-1 near the RGG-free trees, and from 16.7 to 310 mg·L-1 near the trees that were affected by RGG. This suggests that under the conditions of this study, neither the incidence nor the severity of RGG was influenced by high concentrations of Cl- in the soil water.

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