Biocontrol of Rice Seed-Associated Fungal Pathogens Using Green Synthesis Approaches

Rice (Oryza sativa) is a major cereal crop that balances the food demand of the worldwide population. The crop quality drops daily due to their exposure to biotic and abiotic stresses, especially pathogens. It needs to be improved to maintain the consumption level to cope with increasing population demands for food. The current study was designed to analyze the comparison of the effects of green synthesis approaches on pathogens associated with rice seeds. In this study, essential oils were extracted from Cymbopogon citratus, Thymus vulgaris, and Origanum vulgaris medicinal plants and used as fungicides on fungal strains of Aspergillus spp. T. vulgaris effectively controlled the growth of Aspergillus niger, Aspergillus flavus, and Aspergillus terreus as compared with O. vulgaris and Cymbopogon. Further, silica nanoparticles (SiNPs) were synthesized from rice husk to evaluate their antifungal activities. SiNPs were characterized by ultraviolet-visible spectroscopy with a broad peak at 281.62 nm. Fourier-transform infrared spectroscopy spectrum confirms the presence of Si-H, Si-OH, and Si-O-Si bonds functional groups, and SiO4 tetrahedral coordination unit. X-ray diffraction pattern describes the crystalline structure with a sharp peak at 2 theta = 22 degrees. Scanning electron microscopy and energy-dispersive spectroscopy confirmed the spherical shape, size 70-115 nm, and elemental composition with pure silica contents. SiNPs showed no significant antifungal activity against Aspergillus strains. Moreover, Trichoderma was isolated from the rhizosphere of rice fields and showed a surprising antifungal effect against A. terreus, A. niger, and A. flavus. The current study successfully revealed environment-friendly and cost-effective green synthesizing approaches for analyzing biocontrol potential against rice seed-related Aspergillus spp. They will also help to improve pathogen control strategies in other cereals.