*Article Bacillus megaterium***-Mediated Synthesis of Selenium Nanoparticles and Their Antifungal Activity against** *Rhizoctonia solani* **in Faba Bean Plants**

**Amr H. Hashem <sup>1</sup> , Amer M. Abdelaziz 1,\*, Ahmed A. Askar <sup>1</sup> , Hossam M. Fouda <sup>1</sup> , Ahmed M. A. Khalil 1,2 , Kamel A. Abd-Elsalam 3,\* and Mona M. Khaleil 2,4**


**Abstract:** Rhizoctonia root-rot disease causes severe economic losses in a wide range of crops, including *Vicia faba* worldwide. Currently, biosynthesized nanoparticles have become super-growth promoters as well as antifungal agents. In this study, biosynthesized selenium nanoparticles (Se-NPs) have been examined as growth promoters as well as antifungal agents against *Rhizoctonia solani* RCMB 031001 in vitro and in vivo. Se-NPs were synthesized biologically by *Bacillus megaterium* ATCC 55000 and characterized by using UV-Vis spectroscopy, XRD, dynamic light scattering (DLS), and transmission electron microscopy (TEM) imaging. TEM and DLS images showed that Se-NPs are mono-dispersed spheres with a mean diameter of 41.2 nm. Se-NPs improved healthy *Vicia faba* cv. Giza 716 seed germination, morphological, metabolic indicators, and yield. Furthermore, Se-NPs exhibited influential antifungal activity against *R. solani* in vitro as well as in vivo. Results revealed that minimum inhibition and minimum fungicidal concentrations of Se-NPs were 0.0625 and 1 mM, respectively. Moreover, Se-NPs were able to decrease the pre-and post-emergence of *R. solani* damping-off and minimize the severity of root rot disease. The most effective treatment method is found when soaking and spraying were used with each other followed by spraying and then soaking individually. Likewise, Se-NPs improve morphological and metabolic indicators and yield significantly compared with infected control. In conclusion, biosynthesized Se-NPs by *B. megaterium* ATCC 55000 are a promising and effective agent against *R. solani* damping-off and root rot diseases in *Vicia faba* as well as plant growth inducer.

**Keywords:** *Vicia faba*; plant disease; root rot; *R. solani*; Se-NPs; nano-biosynthesis; plant promotion
