Pseudomonas fluorescens–Based Biogenic Silver Nanoparticles: A Green Solution for Brown Leaf Spot Disease in Rice
Academic Background
Rice (Oryza sativa L.) is a globally important food crop, providing a primary source of calories for approximately one-fifth of the world’s population. However, rice production faces various biotic and abiotic stresses, leading to reduced yields. Among these, rice brown leaf spot disease, caused by the fungal pathogen Cochliobolus miyabeanus, is a widespread disease that severely impacts rice yield and quality. Traditional chemical pesticides are not only limited in effectiveness but may also harm the environment. Therefore, the development of environmentally friendly and sustainable disease control strategies has become an urgent priority. Nanobiotechnology, particularly the application of silver nanoparticles (AgNPs), has emerged as a research hotspot due to its high antimicrobial and antifungal activity. This study utilizes a green synthesis method mediated by Pseudomonas fluorescens to prepare AgNPs and evaluates their efficacy in controlling rice brown leaf spot disease.
Source of the Paper
This research was conducted by a collaborative team from multiple institutions, including The American College, SRM Institute of Science and Technology, and Sree Balaji Medical College and Hospital in India; the University of Doha for Science and Technology in Qatar; King Khalid University in Saudi Arabia; and Universiti Malaysia Perlis in Malaysia. The paper was published in 2025 in the journal Bionanoscience, titled “Pseudomonas fluorescens–Based Biogenic Silver Nanoparticles: A Green Solution for Brown Leaf Spot Disease in Rice.”
Research Process and Results
1. Isolation and Identification of Pseudomonas fluorescens
The research team isolated 52 bacterial samples from the rhizosphere soil of rice in the Madurai district of India. Fluorescent strains were screened using King’s B medium. These strains were identified as Gram-negative bacteria through Gram staining and catalase tests, and further confirmed as Pseudomonas fluorescens using standard tests. Among them, strain PF-3 exhibited the strongest antagonistic activity and was selected for subsequent experiments.
2. Isolation and Identification of the Pathogen Causing Rice Brown Leaf Spot
Cochliobolus miyabeanus was isolated from infected rice leaves and identified based on morphological characteristics and cultivation properties. The pathogen appeared as gray-black colonies on PDA medium and grew optimally at 27-30°C. Through dual plate antagonistic assays, 26 strains of Pseudomonas fluorescens with inhibitory effects on the brown leaf spot pathogen were screened, with strain PF-3 showing the most significant inhibition, achieving an inhibition zone radius of 1.5 cm.
3. Biosynthesis and Characterization of Silver Nanoparticles
AgNPs were successfully synthesized by reacting the cell-free culture supernatant of strain PF-3 with a 1 mM silver nitrate solution. The color of the reaction solution changed from light yellow to dark brown, indicating the formation of AgNPs. UV-Vis spectroscopy analysis revealed a distinct absorption peak for AgNPs at 420 nm. Fourier-transform infrared spectroscopy (FTIR) analysis showed the presence of biomolecules such as proteins and polysaccharides on the surface of AgNPs, which play a critical role in the stability and functionality of the nanoparticles. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) further confirmed the spherical morphology and uniform distribution of silver in the AgNPs, with particle sizes ranging from 5 to 50 nm.
4. Evaluation of the Antifungal Activity of AgNPs
Microscopic observations revealed that AgNPs significantly disrupted the hyphal structure of Cochliobolus miyabeanus, causing hyphal tip swelling, bursting, and morphological deformation. These morphological changes indicate that AgNPs interfere with fungal cell integrity, inhibiting their growth and reproduction. The study also found that AgNPs exert their antifungal activity by disrupting cell membranes, inhibiting respiration, and impairing electron transport systems.
Research Conclusions and Significance
This study successfully utilized a green synthesis method mediated by Pseudomonas fluorescens to prepare AgNPs and demonstrated their high efficacy in controlling rice brown leaf spot disease. AgNPs exhibited significant antifungal activity by disrupting fungal cell structure and metabolic functions. This research provides new insights into the development of environmentally friendly and sustainable strategies for agricultural disease control, offering significant scientific and practical value.
Research Highlights
- Green Synthesis Method: The green synthesis of AgNPs mediated by Pseudomonas fluorescens avoids toxic reagents used in chemical synthesis, offering environmental advantages.
- High Antifungal Activity: AgNPs demonstrated significant inhibitory effects on Cochliobolus miyabeanus, providing a novel solution for controlling rice brown leaf spot disease.
- Interdisciplinary Approach: The study combined methodologies from microbiology, nanotechnology, and plant pathology, showcasing the potential of interdisciplinary research in agricultural disease control.
Additional Valuable Information
The research team also explored other potential applications of AgNPs in agriculture, such as their inhibitory effects on other plant pathogenic fungi and their potential in enhancing crop disease resistance. Future studies will further investigate the practical application of AgNPs in field trials and their potential impacts on the environment and human health.
Through this study, the research team has provided an efficient and environmentally friendly alternative for controlling rice brown leaf spot disease, making a significant contribution to the development of sustainable agriculture.