MORPHO-PHYSIOLOGICAL AND BIOCHEMICAL RESPONSE OF CITRUS ROOTSTOCKS TO SALINITY STRESS AT EARLY GROWTH STAGE

A greenhouse study was conducted to determine the morphological, physiological and biochemical responses of four citrus rootstocks viz. Volkameriana (Citrus volkameriana Ten. and Pasq.), Rangpur Lime (Citrus limonia Osbeck), Trifoliate Orange (Pontius trifoliate (L.) Raf.) and Rough Lemon (Citrus jambhiri Lush.) to sodium chloride (NaCl) salinity applied at seedling stage. One year-old uniform citrus seedlings were grown in sand culture irrigated with modified half-strength Hoagland's solution and treated with different NaCl concentrations (0, 75, 100 and 150 mM) for 25 days. Parameters such as plant height, leaf drop and tip burning symptoms differed according to the ability of rootstocks type in coping with salt stress. Salinity significantly (P<0.01) decreased leaf water potential, photosynthetic rate, transpiration rate and stomatal conductance values indicative of serious metabolic effects of salts on the citrus growth at 150 mM (NaCl). The ionic concentration of sodium and chloride was higher in concentration in Volkameriana (9.2 +/- 0.7 and 5.6 +/- 0.15) and Trifoliate Orange (10.2 +/- 0.10 and 6.3 +/- 0.18) than Rangpur Lime (9.9 +/- 0.3 and 4.8 +/- 0.07) and Rough Lemon (16.0 +/- 0.2 and 5.7 +/- 0.10). Calcium and potassium concentrations in all rootstocks decreased with increasing salinity in the plant rhizosphere. Although salinity affected all four rootstock genotypes but Rangpur Lime (8.1 +/- 0.10) followed by Rough Lemon (7.5 +/- 0.60) performed better for potassium uptake as compared to Volkameriana (6.3 +/- 0.30) and Trifoliate Orange (7.4 +/- 0.20). Rangpur Lime even showed new leaf sprouting at the highest level of sodium chloride (150 mM). The rootstock genotype Trifoliate Orange proved to be highly sensitive to NaCl salinity in this study.