Paclobutrazol minimises the effects of salt stress in mango (Mangifera indica L.)

We investigated the effects of paclobutrazol (PBZ) on 1-year-old plants of 'Olour' mango subjected to NaCl stress under polythene tunnel conditions. Plants were treated with two levels of salt [0.0 g NaCl kg(-1) soil (control) or 1 g NaCl kg(-1) soil] and three concentrations of paclobutrazol [PBZ; 0.0 mg l(-1) (control), 750 mg l(-1) or 1,500 mg l(-1)] after 30 d of establishment. Mortality in saline-treated mango plants was reduced significantly (LSD = 8.55; P <= 0.05) following the application of PBZ. NaCl-stress reduced the survival of plants without PBZ treatment by 89%, but only by 28.4% for 1,500 mg l(-1) PBZ-treated plants. PBZ-treated plants also showed less defoliation, and fewer leaves per plant exhibited salt stress symptoms. It was also evident that treatment with PBZ increased the relative water and chlorophyll contents of mango seedlings, and reduced membrane injury, under salt stress. Furthermore, saline treatment without PBZ increased the Na+ and Cl- ion contents of leaves and roots; however, application of PBZ consistently and significantly lowered these ion contents (P <= 0.05). The Na+ content of leaves on saline-treated plants was reduced by 1.96- to 2.12-fold, whereas Cl- ion contents were reduced by 22 - 39% by PBZ treatment compared to salt-treated seedlings without PBZ. Our results suggest a role for PBZ in promoting the avoidance of salt stress in mango by increasing the levels of photosynthetic pigments, water content, K+ uptake and accumulation, and by reducing defoliation, the membrane injury index, and the uptake and accumulation of harmful Na+ and Cl- ions. These findings may be used to improve the yields and quality of mango trees grown in salt-affected areas.