Unraveling the effects of melatonin on drought-stressed pear rootstocks: A comparative analysis of Dargazi and Pyrodwarf

Abstract

Drought stress is known as one of the major challenges in most fruit-growing areas. This research aimed to investigate the amelioration effect of pre-drought exogenous melatonin application on the physiological and biochemical response of `Dargazi’ seedling and `Pyrodwarf’ clonal pear rootstocks, grown under water stress and controlled greenhouse conditions. Drought stress was applied by withholding irrigation water for 40 days on one-year-old un-grafted seedlings and clonal pear rootstocks. Gas exchange, chlorophyll content, relative water content, lipid peroxidation, and enzyme antioxidant activity were examined. Pre-drought treatment of melatonin significantly increased drought tolerance, successfully recovered the lost growth and considerably improved photosynthetic efficiency. The adverse effect of drought stress was ameliorated by melatonin through the possible osmotic adjustment such as the increase of proline (102 and 92 g/g FW for `Dargazi' and `Pyrodwarf' respectively) and soluble sugars as well as the improvement of the antioxidative defense system through the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). The `Dargazi’ seedling rootstock showed better tolerance to drought stress with higher photosynthesis, leaf water content, chlorophyll content, antioxidant enzyme activity, lower lipid peroxidation, and H2O2 generation than the Pyrodwarf clonal rootstock. Also, melatonin ameliorated the negative effect of water stress on photosynthesis and growth parameters through the possible inducing osmotic adjustment and anti-oxidative system under the severe drought stress condition on pear rootstocks. SOD, APX, POD, and CAT activities in Dargazi rootstock were significantly higher than those in control plants by 76.1 %, 34.9 %, 20.93 %, and 124.42 % respectively. Similarly, SOD, APX, POD, and CAT in Pyrodwarf pear rootstock increased in enzyme activities by 56.92 %, 24.37 %, 35.53 %, and 259.52 %, respectively. It is concluded that melatonin application as a pre-drought treatment mitigates the negative effects of drought stress in both rootstocks and the Dargazi rootstock exhibits remarkable resilience to drought stress.