*2.3. Control of Rhizoctonia solani by Se-NPs*

### 2.3.1. Source of Pathogen and Culture Conditions

*Rhizoctonia solani* RCMB 031001 was purchased from the Regional Center for Mycology and Biotechnology (RCMB), Al-Azhar University, Cairo, Egypt. *R. solani* was cultured on potato dextrose agar medium (PDA) plates, incubated for 3–5 days at 28 ± 2 ◦C, and then kept at 4 ◦C for further use [42–45].

2.3.2. In Vitro Assessment of Antifungal Activity and Growth Inhibition

• Well diffusion method

The well diffusion method was applied to study the antifungal activity of biosynthesized Se-NPs [46] with a few modifications. *R. solani* was inoculated on PD broth medium and then incubated at 28 ± 2 ◦C for 3–5 days. Fungal inoculum of *R. solani* RCMB 031001 was spread thoroughly on the sterilized solidified potato dextrose agar (PDA) medium. At the same time, eight wells with 5.5 mm diameter were made using a sterile cork-borer on each agar plate (120 mm). The wells were filled with 50 µl of different concentrations of Se-NPs individually with triplicates. The culture plates were incubated at 25 ◦C for 7 days, and the zones of inhibition were observed and measured.

• Radial growth method

PDA medium was prepared and amended with different concentrations of Se-NPs (1, 0.5, 0.25, 0.125, and 0.0625 mM) before the pouring stage. After medium solidification, culturing of *R. solani* was carried out according to Joshi et al. [47]. The inhibition percentage of pathogen growth was calculated using the following equation:

Inhibition of pathogen growth (%) = Growth in the control − Growth in the treatment Growth in the control <sup>×</sup> 100.
