Effect of salt stress on physiological responses of four citrus rootstock plantlets under in vitro condition

Salinity is one of citrus production problems in the world, and the tolerance or resistance mechanism of citrus rootstocks to salinity is not well known. In this study, the physiological responses of four citrus rootstocks, Sour orange (Citrus aurantium.L), Poncirus (Poncirus trifoliate Raf), Citromelo (Citrumelo) and Citrange (Citranges), to salinity stress was investigated in a factorial experiment based on completely randomized design under in vitro conditions. The explants were prepared from all four rootstocks and transferred in a Murashige and Skoog (MS) solid culture medium containing 8.9 μM BA and 0.5 μM NAA with different concentrations of sodium chloride (0, 50, 100 and 200 mM) in three replications. Based on obtained results of experiment, plantlets fresh and dry weight, water content, leakage and photosynthetic pigments such as chlorophyll a, chlorophyll b and carotenoid had a negative correlation with salinity concentration and concentration of sodium ion in the tissue of the leaves. Although leakage increased with increasing concentration of sodium chloride on all four rootstocks, the Sour orange rootstock statistically showed the least leakage as compared to other rootstocks. In all salinity treatments, the amount of rootstocks photosynthetic pigment reductions was statistically significant (p ≤ 0.01) as compared to the control. Among the tested rootstocks, the amount of photosynthetic pigments in the Citrange rootstock was higher than other rootstocks. In conclusion, Citrange and Sour orange rootstocks showed better resistance to the damages caused by salt stress.