Physiological and biochemical responses of citrus rootstocks under salinity stress

Physio-biochemical response of indigenous citrus rootstocks namely Attanni-1 (Citrus rugulosa), Attanni-2 (C. rugulosa) and Jatti khatti (C. jambhiri) under NaCl stress was studied. The experiment was performed on 1-year-old potted plants which were irrigated with non-saline and saline (25 and 50 mM NaCl) water. Results indicated that salt stress had a pronounced effect on different physiological and biochemical parameters of these rootstocks. The highest MII (0.159) was recorded in Jatti khatti under 50 mM salinity followed by Attani-2 and Attani-1. There was almost two-fold reduction in RWC in the Jatti khatti rootstock under 50 mM salinity as compared to Attani-1 and Attani-2 rootstocks. The maximum (2.22 mg g(-1) FW) total chlorophyll was recorded in Jatti khatti (control) followed by non-salinised Attani-1 and Attani-2. Salt stress induced a sharp reduction in total chlorophyll content in Jatti khatti as compared to other two rootstocks. The highest SOD (45.67 units mg(-1) protein min(-1)) and CAT (5.34 p moles H2O2 hydrolized mg(-1) protein min-1) activities were recorded in the Jatti khatti under 50 mM NaCl salinity followed by Attani-2 and Attani-1. CAT activity declined in different rootstocks at 50 mM salinity. There was a sharp increase in salt induced POD levels in different rootstcoks upto 25 mM salinity with the highest activity (0.75 Absorbance units g(-1) FW) in Jatti khatti followed by Attani-2 rootstocks. Based on observations on membrane stability, relative water content, photosynthetic pigments, proline content and activity of antioxidant enzymes, the relative salt tolerance of citrus rootstocks was adjudged to decrease in the following order: Attanni-1>Attanni-2> Jatti khatti.