N. J.J. Combrink, N. Labuschagne, R. O. Barnard & J. M. Kotzé
South African Journal of Plant and Soil
Most of the world’s citrus is irrigated (Furr & Ream, 1969) and salt accumulation often results from use of poor quality irrigation water and inadequate soil drainage (Bernstein, 1975; Backlund & Hoppes, 1984). Citrus is generally considered to be a salt sensitive plant (Bernstein, 1969; Furr & Ream, 1969; Kirkpatrick & Bitters, 1969) although a wide range of salt . tolerance exists among citrus rootstocks (Cooper, 1961; Embleton, Labanauskas & Bitters, 1962; Peynado & Roger, 1962). Most rootstocks are adversely affected by salinity levels at which conductivity of the satl.l,rated soil extract (ECe) is about 250 – 300 mS m-I (Bernstein, 1975),. ‘It has been reported that heavy losses in production can occur even in the absence of visible toxicity symptoms such as leaf burn (Harding, Pratt & Jones, 1958; Pearson & Huberty, 1959; Peynado & Roger, 1962; Shalhevet, Yaron & Horowicz, 1974).
Furthermore, it has been demonstrated that salinity can increase the severity of several root diseases (MacDonald, 1982; Willers, 1982; Blaker & MacDonald, 1986). In the light of similar problems at Zebediela citrus estate, in the Northern Transvaal area of South Africa, studies have been undertaken to investigate the role of chloride in citrus production. The purpose of this study was to evaluate the chloride tolerance of four primary rootstocks presently in use at Zebediela and to determine a chloride level at which rootstocks are adversely affected without showing any visible toxicity symptoms. In a subsequent study the effect of chloride stress on the severity of citrus root diseases will be investigated.