Drought tolerance in citrus rootstocks is associated with better antioxidant defense mechanism

Citrus is one of the major fruit crops grown worldwide. Citrus trees are affected by different abiotic stresses including drought which decrease its yield. In this study, six different citrus rootstocks (Volkameriana lemon, Brazilian sour orange, Carrizo citrange, Eureka lemon, Gada dahi, and Rangpur lime) were subjected to drought stress (24 days) and leaf relative water content (LRWC), chlorophyll 'a' and 'b', antioxidant capacity (AC), total phenolic content, and proline content (PRO) were measured. Hydrogen peroxide (H2O2), lipid peroxidation (MDA), total soluble proteins (TSP), and enzymatic antioxidant activities, such as superoxidase dismutase (SOD), catalase (CAT), and peroxidase (POD), were measured in leaves and roots of the rootstocks. Drought-stressed Volkameriana lemon had the minimum LRWC but higher SOD activity in its leaves. Carrizo citrange possessed the minimum amount of Chl 'a' and 'b' in leaves and exhibited lesser MDA and H2O2 in roots but greater TSP content in leaves and roots. SOD, CAT, POD, PRO, MDA, H2O2, and AC decreased in the leaves of Eureka lemon and Rangpur lime under drought stress. MDA and H2O2 contents were observed higher in leaves of Brazilian sour orange (a drought sensitive rootstock). However, higher SOD activity in roots and higher CAT and POD activities in leaves and roots were recorded in Carrizo citrange (a drought-tolerant rootstock). The results indicated that all the studied rootstocks were different in their defense mechanism. Tolerant rootstocks exhibited less amount of MDA and H2O2 and more antioxidant enzymatic activities (SOD, CAT, and POD) to cope with reactive oxygen species produced during drought stress.