Selection of Stable Salt-Tolerant Callus Cell Lines and Embryos in Citrus sinensis and C. aurantium)

Several callus cell lines of «Shamouti" (Citrus sinensis Osbeck)and one cell line of «Sour orange» (c. aurantium)capable of growing in the presence of up to about 10gl-1 NaCl, were obtained by repeated exposure of the cultured ovular cells to a medium containing salt. Gamma irradiation prior to exposure to salt gave no selective advantage. Increased tolerance for salt was retained even after three consecutive transfers in medium without salt, indicating isolation of genetic variants exhibiting stability of the salt-tolerance trait. Replacing NaCI by KCI resulted in significantly increased sensitivity to salt. However, when Cl-was replaced by S04 -2, the NaCl-tolerant cell lines grew well on either Na2S04 or K2S04. The salt-sensitive line can be induced to undergo embryogenesis in the presence of galactose. The salt-tolerant cell lines still preserve the capacity to regenerate embryos, though to a differ-ent degree. Some of these lines regenerate embryos in the presence of galactose, while others require the combination of salt and galactose in the medium. Embryos regenerated from salt-tolerant callus cells survived and grew better in saline medium than did embryos regenerated from the original salt sensitive callus.