Wangchu, L.Begane, NesaraHazarika, B.N.2020-02-042020-02-042019-12-09http://krishikosh.egranth.ac.in/handle/1/5810142448All the stress levels enhanced ROS, exposing plants to oxidative damage and thereby affecting morphophysiological parameters, lipids and protein content of the plant. To cope up with the stress, seedlings produced osmoprotectants, enzymatic and non-enzymatic antioxidants.Drought and combined stress had more inhibiting effect on seedlings growth as compared to salt stress and it enhanced with the increasing exposure time. However, in Rangpur lime and Rough lemon, lower level of NaCl (75 mM) alleviated harmful effects of lower level of PEG-6000 (-1.0 MPa) when given in combination. Hence, seedlings performed better under -1.0 MPa PEG + 75 mM NaCl than drought stress alone (-1.0 MPa).On comparing citrus species, Rangpur lime and Rough lemon had better endurance towards stress by maintaining higher level of antioxidants and osmoprotectants.The present investigation “Studies on Tolerance Ability of Citrus species against Salinity and Drought” was carried out at the “Department of Fruit Science”, during the year 2016-19. This investigation was taken up with an objective to identify citrus species tolerant to salinity and drought, to study the effect of salinity and drought on the seedling growth of different citrus species, to study the tolerance levels of different citrus species against different levels of salinity and drought, and; to study the physiological and biochemical responses of citrus species against salinity and drought. During this study, salt stress, drought and their combination was given to three citrus species (Rangpur lime, Rough lemon and Indian wild orange). The different levels of polyethylene glycol-6000 [-1.0 MPa (D1) and -1.5 MPa (D2)] was used for inducing drought stress, while various levels of sodium chloride [75 mM (S1) and 100 mM (S2)] was used for inducing salt stress and untreated seedlings were served as control. The seedlings exposed to stress conditions were uprooted after 48 hrs and 30 days. The seedlings were subjected to analysis of morpho-physiological parameters like shoot and root length, shoot and root fresh and dry weight and relative water content. Biochemical parameters include photosynthetic pigments (chlorophylls and carotenoids), total soluble proteins, lipid peroxidation, leaf carbohydrate, proline, reactive oxygen species (hydrogen peroxide, superoxide anion and hydroxyl free radical), enzymatic antioxidants (CAT, SOD, APX and GR) and non-enzymatic antioxidants (ascorbic acid and tocopherol).ennullThesis