The current study explores the potential impact of seed priming with silicon nanoparticles (SiNPs, 0, 100, 200, 500mg/L) and silicate (Si, 0, 1, 1.5, 2mg/L) under polyethylene glycol (PEG)-induced drought stress (0, –0.5, –1, and –1.5MPa, respectively, control, mild, moderate and severe drought stress) on germination features and vigor index of marigold (Calendula officinalis L.). The study was performed in a factorial experiment based on completely randomized design (CRD) with four replications. Based on scanning electron microscopy (SEM) analysis, application of SiNPs at high level in seeds subjected to the severe drought stress clearly revealed the greater deposition of SiNPs on root cell walls compared to the mild or moderate drought stress. The cumulative germination in response to various concentrations of Si and SiNPs showed different germination patterns under drought stress intensities. Two-way interaction of SiNPs and drought stress significantly (P< 0.01) affected the mean germination time only, however, interaction of Si and drought stress significantly influenced germination rate (P< 0.05) and germination index (P< 0.01). The vigor index (VI) based on seedlings length (SL) and dry weight (DW) at 14 days after planting were significantly higher in Si- and SiNPs-treated seeds at 2 and 500mg/L compared to the other treatments, respectively. In both Si and SiNPs treatments, VI-SL and VI-DW showed positive and significant correlation (r0.01= 0.737 and r0.01= 0.859) and (r0.01= 0.639 and r0.01= 0.821) with germination percentage under drought stress, respectively. These findings will open the opportunity of using Si and SiNPs as priming agents to enhance seed germination and improve seedling growth under water deficit stress.
