The objective of this study was to investigate the effect of arbuscular mycorrhizal fungi (AMF from Glomus genus) inoculation on salt tolerance and the expression of CaSISP gene in sour orange (Citrus aurantium L.) seedlings. Forty-day-old sour orange seedlings were inoculated with G. mosseae + G. intraradices, G. mosseae + G. hoi, G. intraradices + G. hoi, G. mosseae + G. intraradices + G. hoi and kept for 175 days, then treated with 0 (control), 35 and 70 mM NaCl. After 45 days of salinity treatment, some physiological, biochemical and growth parameters as well as the expression pattern of Stress-Inducible Small Protein (SISP) gene were determined. Under salt stress, mycorrhizal inoculated plants had higher growth, higher chlorophyll content, better water status, higher gas exchange capacity (increased photosynthetic rate, stomatal conductance and transpiration rate), lower electrolyte leakage, malondialdehyde and hydrogen peroxide contents and higher osmolytes accumulation and antioxidant defense systems response compared to non-mycorrhizal treated plants (control). Moreover, abscisic acid levels were lower in colonized plants, indicating that they were less stressed than the controls. On the other hand, we demonstrated for the first time that the expression of CaSISP gene was influenced by both AMF symbiosis and salinity stress. Our study showed that the plants inoculated with the triple combination of fungi based on some of morphological, physiological and biochemical characters were more tolerant to salt stress than the others suggesting the application of AMF colonization as a practical way to improve citrus production under salt stress condition.
