Physiological response of mango transplants to phytohormones under salinity stress

Salinity is an emerging and highly complex phenomenon affecting plant production and global food security. Here we demonstrated the effects of phytohormones (naphthalene acetic acid (NAA), indol-3-Acetic acid (IAA), and salicylic acid (SA) application and grafting of two mangoes (Mangifera indica L.) cultivars onto a relatively salt-resistant Sukkary rootstock, under saline groundwater irrigation conditions. The experiment was carried out by exposing 1.5-years old mango cultivars (cv., Keitt and Naomi) to increasing (100, 200, and 300 mg L-1) doses of NAA and IAA, and a single dose of SA (200 mg L-1) at three growth stages (i) first week after transplantation, (ii) and (iii) at 30-days interval. Results showed that the exogenous application of IAA at 300 mg L- 1 while NAA and SA application at 200 mg L-1 resulted in the highest leaf nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) and lowest leaf sodium (Na) content in both cultivars. The cv. Keitt showed the highest carbohydrate and protein contents, chlorophyll a, b and carotenoids, catalase (CAT), and peroxidase (POD) activity by applying 300 mg L-1 IAA, 200 mg L-1 NAA, and SA. While the cv. Naomi showed the greater carbohydrate and protein contents, CAT, POD enzymes, and plant pigments by applying NAA at 200 mg L-1.Together, our results suggest that foliar application of phytohormones can potentially alleviate salinity stress in grafted mango cultivars under saline irrigation conditions.