الفهرس 
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Abstract
Various biotechnological tools have been utilized to evaluate and improve banana and citrus germplasm. We investigated various techniques to manage abiotic stress. These techniques included : 1) studying the role of silicon nanoparticles to mitigate abiotic stress in banana and citrus crops, 2) evaluating the performance of a putative new citrus rootstocks produced via conventional breeding under saline stress conditions and citrus greening disease (HLB), 3) investigating the role of NPR1 gene in salt stress tolerance mechanism. The positive effects of SiO2-NPs application were confirmed in both in vitro and ex vitro exposure of SiO2-NPs alleviated the adverse effect of abiotic stress by improving the photosynthesis process, decreasing lipid peroxidation and cell wall damage, and increasing K+ concentration and K+/Na+ ratio. In comparison between citrus rootstocks (HS1, S10, HS17, HC15, VOLK, CLEO and Czo) under different levels of NaCl. Our findings reveal that salt stress reflected in obvious impairment in photosynthesis and inhibition of stomatal conductance, transpiration, and chlorophyll fluorescence, with increases in the concentration of MDA highlighting the lipid peroxidation and oxidative damage of cell membranes. However, the adverse effects of salt stress could be repaired via various internal mechanisms in the cell, such as antioxidant accumulation and osmoprotectants activity. In this study, HC15 showed increased accumulation of phenolic compounds and proline with decreased lipid peroxidation. Additionally, our results revealed significant differences in the physiological, biochemical, and molecular analysis following NaCl treatment or CaLas infection among the different seedling derived lines of S10 rootstock where ‘Valencia’ scions grafted to it was observed to be highly susceptible to HLB. Overexpression of NPR1 induced antioxidants genes and Na+ co-transporters Our results suggest that NPR1 is an important candidate to improve citrus tree growth and reduce oxidative damage under salt stress.