Seed priming by magnetic fields has been introduced as a new, efficient and suitable method, particularly for organic and biodynamic systems to invigorate of seeds and also to improve seedling establishment and crops yield. Magnetic treatments also are used to enhance tolerance of crop plants to many biotic and abiotic stresses. On the other hand, in modern agro-ecological systems, silica-based fertilizers, especially in Nano-forms, are utilized to boost the growth and production of plants and to improve plants tolerance to various environmental stresses. In order to investigate the single and combined effects of magneto-priming and silicon dioxide (SiO2) nanoparticles (NPs) on some physiological responses of water-stressed sesame, a factorial experiment based on completely randomized design with three replicates was carried out under greenhouse conditions. For this aim, at first, seeds of sesame exposed to a static magnetic field with a magnitude of 75 mT for 1h, then seedlings were treated with four doses of SiO2 NPs (un-application of SiO2 (control) and 10, 50 and 100 mg/l) at the stage of full establishment (viz. formation of 6 non-cotyledon leaves in plants) and immediately exposed to water stress at two levels (control (FC 90%) and water stress (FC 50%). Then in two stages of flowering and fruit set (capsule formation), Chlorophyll content was measured by a handy SPAD device and afterward chlorophyll fluorescence parameters including minimum fluorescence (F\\\'o), maximum fluorescence (F\\\'m), variable fluorescence (F\\\'v) and Maximum quantum efficiency of photosystem II (F\\\'v/F\\\'m) were measured by a portable fluorimeter. Results showed that at the flowering stage of sesame, the chlorophyll content in magneto-priming treatment was higher than un-magneto-priming under non-stress and water stress conditions almost in all concentrations of SiO2 NPs. The most chlorophyll content was in water stress, magneto-priming and 10 mg/l of SiO2 NPs. Also under water stress conditions, the F\\\'v/F\\\'m ratio in magneto-priming treatment and in all doses of SiO2 nanoparticles was higher than un-magneto-priming. In the fruit set stage, magneto-priming almost at all doses of SiO2 nanoparticles reduced the minimum fluorescence of sesame leaves compared to un-magneto-priming under non-water stress and water stress conditions. F\\\'v/F\\\'m ratio in two treatments of un-magneto-priming, non-water stress and 50 mg/l SiO2 NPs and the magneto-priming, non-stress and un-application of SiO2 NPs was similar and maximum. These cases indicate the positive effects of magneto-priming and silicon dioxide nanoparticles on some physiological traits affecting water tolerance, particularly at the flowering stage of sesame, which is more vulnerable to water scarcity.

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