Low pH and Water Stress Induced Morpho-Physiological Response in Some Traditional Citrus Species of Assam, India

Citrus is considered to have originated in north-eastern India which is recognized for having a wide variety of Citrus plants. Assam (India) is also a rich biodiversity hotspot of different Citrus species. The geographic region of this state is favored by a very suitable climatic condition for the growth of different crop plants including Citrus. But, being a flood prone area, every year Assam faces a destruction of large scale of crop plants. The increasing problem of climate change also affects this region to a greater extent from the past few years. For this reason, some unpredictable environmental conditions are experienced by this area which has become a cause of unfavorable growth of plants. Since Citrus is a very significant fruit crop of Assam, therefore, study on the effect of abiotic stress on this species is necessary. The present investigation includes a study on the morpho-physiological response of five different Citrus species to three different abiotic stresses including submergence, drought and low pH. Growth parameters like leaf fresh weight and dry weight, root fresh weight and dry weight were measured which revealed decreasing value in the stress conditions followed by an increased rate in the recovery. Similarly, the stress conditions were found to affect the physiological parameters including total chlorophyll content, relative water content (RWC), membrane stability index (MSI), relative electrolytic conductance (REC). Maximum quantum efficiency (Fv/Fm) of the Citrus plants under stress was found to be notably reduced which further increased in recovery. The key parameters mostly affected by stress were found in principal component analysis (PCA). Hydrogen peroxide (H2O2) and malondialdehyde (MDA) content of leaves and roots were highly affected by low pH and drought stress, whereas maximum quantum efficiency (Fv/Fm), membrane stability index (MSI) and relative water content (RWC) were come out to be the principal factors affected by submergence stress. Nevertheless, a good recovery rate was observed in the Citrus species. From this study the traditional Citrus species of Assam were discovered to possess significant tolerance ability against abiotic stresses.