The impacts of different concentrations of bulk and nanosized TiO2 on seed germination and seedling growth of wheat were studied in a randomized completely design with four replications in the College of Agriculture, Ferdowsi University of Mashhad, Iran, in 2011. The experimental treatments included five concentrations of bulk (1, 2, 10, 100, and 500 ppm), five concentrations of nanosized TiO2 (1, 2, 10, 100, and 500 ppm), and control (without any TiO2). Results indicated that among the wheat germination indices, only mean germination time was affected by treatments. The lowest and the highest mean germination time (0.89 vs. 1.35 days) were obtained in 10 ppm concentration of nanosized TiO2 and control treatments, respectively. In addition, shoot length, seedling length, and root dry matters were affected by bulk and nanosized TiO2 concentrations, significantly. Shoot and seedling lengths at 2 and 10 ppm concentrations of nanosized TiO2 were higher than those of the untreated control and bulk TiO2 at 2 and 10 ppm concentrations. Employing nanosized TiO2 in suitable concentration could promote the seed germination of wheat in comparison to bulk TiO2 but in high concentrations had inhibitory or any effect on wheat.

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