**1. Introduction**

Rice (*Oryza sativa* L.) is the largest food crop in the world [1,2]. One of the basic hindrances to the growth of rice crops is the infection of various fungal diseases, particularly rice blast disease caused by *Magnaporthe oryzae*, which poses a serious threat to global food safety through the loss of 10–30% of rice production, enough rice for about 60 million people [1,3,4]. Current control of rice blast disease mainly depends on the use of fungicides. However, the desired goal of controlling the disease has not so far been achieved and there are serious consequences of the excessive use of fungicide on humans, ecosystems and the production of fungicide-resistant strains [5,6]. For all these risks, it is extremely important to find an alternative way to control rice blast disease. Nanotechnology can revolutionize the agricultural and food industry with new tools such as molecular plant disease management, fast disease revelation and the improvement of plants' ability to uptake nutrients. Furthermore, nanotechnology can enhance

our biological knowledge of a variety of plants and therefore can improve crops or nutritional values as well as develop improved systems to monitor environmental conditions and enhance plants' ability to uptake nutrients or pesticides [7]. Therefore, the application of nanotechnology in agriculture for the control of plant diseases is a safe and eco-friendly alternative to synthetic chemical fungicides [8,9]. It has been instrumental in suppressing many of the fungal pathogens that attack the plants, causing them huge loss. For example, silver nanoparticles (AgNPs) had a significant effect in suppressing many of the air, seed and soil-borne fungal plant pathogens [9,10]. AgNP synthesis was documented using various methods including physical, chemical, and biological [11,12]. However, biological methods are safer than conventional physical and chemical methods [13,14]. It is a simple process (single vessel installation), rapid, cheap and eco-friendly. Furthermore, the polyphenols and various proteins existent in bio-sources work as a reducing agent, decreasing the use of dangerous external chemical reducing agents and, thus, toxicity. The green synthesis procedure does not require any additional capping agents, which further reduces the cost and simplifies the synthetic process. In contrast, chemical and physical methods are highly restricted in large scale applications, and also have high cost, use high energy, waste time and have difficulty in removing waste [15]. One of the most important biological methods to biosynthesize silver nanoparticles is the use of microorganisms such as bacteria, fungi and algae [11]. In this study, for the first time we biosynthesized new AgNPs using cell-free supernatants (CFSs) of endophytic bacterium *B. endophyticus* strain H3 and examined their characterization as a fungicide to inhibit *M. oryzae*.
