An integrated diagnostic approach to understand drought tolerance in mulberry (Morus indica L.)

Four popular mulberry cultivars (Morus indica L. cvs.V-1, MR-2, S-36 and K-2) were assessed for drought tolerance with an integration of selective approaches. The potted plants were subjected to two watering treatments for 75 days: control pots were watered up to 100% field capacity (FC) and stressed pots were maintained at 25–30% FC. Net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (E) and instantaneous water use efficiency (WUE_i) were the key parameters to assess photosynthetic gas exchange performance. Drought caused marked down-regulation in leaf gas exchange in all cultivars (cvs) except V-1 which maintained better P_n, g_s, E and higher WUE_i under severe water deficit. All the four cvs also showed differential antioxidative responses under water stress. Higher concentrations of carotenoids, ascorbic acid, glutathione, α-tocopherol and proline were observed in the leaf extracts of V-1, while minimum accumulation of those metabolites was recorded with K-2 and S-36. An endogenous loss of α-tocopherol and higher lipid peroxidation were encountered in K-2, S-36 and MR-2, whereas V-1 showed minimum lipid peroxidation under water deficit regimes. Comparative morpho-anatomical analysis revealed a well-developed root system and a better anatomical architecture in V-1 which could further contribute tolerance during drought stress.