Incidence of Rio Grande Gummosis of grapefruit is not associated with concentrations of anions in soil water

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 Gumm osis (RGG) in grapefruit (Citrus paradisi MacFadyen) trees. White 'Marsh' g rapefruit 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 d epths. The severity of RGG was evaluated 18 months following the applicatio n of various rates of KCI. The concentration of Cl- in soil water samples v aried from 16.2 to 617 mg.L-1, with mean concentrations across all treatmen ts of 160.7 and 188.4 mg.L-1 for 120- and 180-cm depth water samples, respe ctively. The concentrations of C1- and other anions (NO3-, PO43-, SO42-) in soil water at either 120- or 180-cm depth were poorly related to the incid ence or severity of RGG (R = -0.10 to -0.28), Chloride concentrations in th e 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 sev erity of RGG was influenced by high concentrations of Cl- in the soil water .