Endophytic fungi induce salt stress tolerance in greenhouse-grown basil

In many irrigated regions of Mediterranean areas, vegetable farmers are forced to use low quality water (often with elevated salinity) for their crops with important losses in productivity. Sweet basil (Ocimum basilicum L.) is one of the most important aromatic herbs cultivated in Italy under both open-field and protected conditions. The application of endophytic fungi such as mycorrhizal fungi and Trichoderma could be an efficient tool to mitigate the detrimental effect of salinity. A greenhouse experiment was carried out to assess the influence of co-inoculation of endophytic fungi and plant growth promoting rhizobacteria on yield and quality traits under non-saline (1 mM NaCl) and saline (40 mM NaCl) conditions. Increasing the NaCl concentration in the nutrient solution in both inoculated and non-inoculated plants decreased the yield and growth parameters but increased the quality traits in particular the hydrophilic and lipophilic antioxidant activities and total phenols. The microbial-based biostimulant markedly enhanced the marketable fresh yield by 17.0% compared to control plants. The better crop performance of inoculated basil has been attributed to a better pigment biosynthesis (i.e., higher SPAD index). On the other hand, the nitrate content in microbial biostimulant basil plants was significantly reduced by 16.1%, whereas the total phenols increased by 7.7% compared to untreated plants. Overall, the use of beneficial microorganisms could be adopted as a sustainable tool in vegetable cropping systems to mitigate the detrimental effect of saline water.