Combined Use of Arbuscular Mycorrhizal Fungi Inoculants and Potassium Silicate for Improving Drought Tolerance in Cucumber

Drought stress is one of the most serious abiotic stresses that cause significant reductions in plant growth and yield in many areas around the world. Arbuscular mycorrhizal fungi (AMF) improve plant drought tolerance by extending the root zone through extraradical hyphae exploration of soil micropores. This study evaluated the combined application of AMF and potassium silicate (PS) to improve the drought tolerance of cucumber plants. Cucumber plants were grown under two watering regimes: drought-stressed 60% water holding capacity (WHC) and unstressed 80%WHC, and three mycorrhizal inoculation treatments (control, native AMF: quick root colonizer species, and commercial AMF) with or without potassium silicate application (100 mL/pot, con. 40 mL/L). Drought stress significantly reduced plant height, biomass, and photosystem II efficiency, while it increased the content of leaf glycine betaine and catalase activity. Generally, AMF inoculation significantly improved plant growth, SPAD, photosystem II efficiency, concentration of proline, glycine betaine, and catalase activity, and the native species exhibited comparable effects to commercial species for most variables studied. Contrary to our expectations, PS application alone did not improve plant growth, except for increased photosystem II efficiency, but root fresh and dry weights were reduced. Under drought stress, combination of PS and AMF significantly improved plant height, shoot fresh weight, SPAD value, glycine betaine, and catalase activity compared to PS alone. Our results highlight that the combined application of PS and AMF inoculants can protect cucumber seedlings from drought stress; however, further research is needed to optimize the PS application method and dosage and to investigate their long-term effects on plant growth and yield under field conditions.