Morphological and physio-biochemical responses of cactus pear (Opuntia ficus indica (L.) Mill.) organogenic cultures to salt and drought stresses induced in vitro

Salinity and drought are important abiotic stress factors whose frequency and severity have increased due to climate change. Today, cultivating plants with increased stress resistance is a global priority. Herein, the morphological and physio-biochemical responses of cactus pear adventitious shoots to different levels of salt and drought stresses were investigated. Sodium chloride (NaCl; 2.5–10 g·L−1) and polyethylene glycol (PEG; 50–150 g·L−1) were added to the culture medium at different growth stages (shoot bud proliferation, and shoot elongation and rooting) and over different periods (1–3 weeks). Salt and drought stresses reduced shoot proliferation, growth, fresh and dry weights. Increasing the concentration of NaCl to 10 g.L−1 and the duration of stress to 3 weeks significantly decreased the survival rate of organogenic cultures (75%) and isolated shoots (62.25%). Drought stress did not significantly affect the survival rate of explants (95.75–100%). Notably, drought stress promoted rhizogenesis of organogenic cultures (31.25–62.50%; no root formation in control group) and isolated shoots (95.75–100%; control group, 91.63%). As regards to the physio-biochemical properties of explants, significant variations were observed. After one week of stress, there was a notable decline in the levels of glycine betaine, proline and carbohydrates. However, increasing the duration of stress promoted their accumulation, which can be taken as an indicator of adaptation to stress. The total protein and chlorophyll a contents decreased under stress conditions, while chlorophyll b showed random variations. The regenerated plants were successfully established in the greenhouse and then transferred to soil where they produced new cladodes.