Influence of Salt Stress on Growth and Mineral Uptake by Two Citrus Rootstocks under In Vitro Conditions

Growth and potential of mineral uptake by tow citrus rootstocks [sour orange (Citrus aurantium L.) and trifoliate orange (Poncirus trifoliate Raf.)] was investigated under in vitro salt stress. A factorial experiment in a completely randomized design was conducted in tissue culture laboratory of University of Zanjan. First, explants (nucellar seedling obtained from seeds) of both rootstocks were proliferated on Murashige and Skoog (MS) solid medium containing 8.9 μM benzyladenine (BA) and 0.5 μM naphthaline acetic acid (NAA). After proliferation, nucellar seedlings were subcultured to same proliferation culture medium with different concentrations 0, 50, 100, 150 and 200 mM sodium chloride (NaCl) as salinity treatment. At the end of experiment (6th week), growth parameters (dry weight, shoot length and shoot number), concentrations of macro and microelements, sodium and chlorineions in plant tissues (as uptake index) were measured. There were significant differences between two rootstocks in control and other treatments on growth parameters, mineral uptake, sodium and chlorine ions. At 200 mM sodium chloride, explants grown of trifoliate orange were stopped after three weeks and gradually at 5th week were necrotic. The highest and lowest dry weight and concentration of mineral (uptake index) were observed in the control and of 200 mM concentration of sodium chloride, respectively, while copper uptake was not affected by salinity stress. In comparison with trifoliate orange, sour orange was more capable rootstock for nitrogen and phosphorous uptake under salinity stress. Also, accumulation of sodium and chloride ions in sour orange tissue was significantly lower than trifoliate orange. Based on the obtained results, it is concluded that sour orange rootstock is more tolerant to NaCl salinity than trifoliate orange.