The synthesis of metal oxide nanoparticles with the use of plant extract is a promising alternative to the conventional chemical method. This work aimed to synthesize zinc oxide nanoparticles (ZnONPs) using plant extract of chamomile flower (Matricaria chamomilla L.), olive leave (Olea europaea) and red tomato fruit (Lycopersicon esculentum M.). The synthesized ZnONPs were characterized by UV–Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with EDS profile. The XRD studies confirmed the presence of pure crystalline shapes of ZnO nanoparticles. The ZnONPs synthesized by Olea europaea had the least size range of 40.5 to 124.0 nm as revealed by the SEM observation while XRD revealed a dominant average size of 48.2 nm in the sample which is similar to the size distribution analysis obtained from TEM. The antibacterial effect of ZnONPs synthesized by Olea europaea on Xanthomonas oryzae pv. oryzae (Xoo) strain GZ 0003 had an inhibition zone of 2.2 cm at 16.0 µg/ml which was significantly different from ZnONPs synthesized by Matricaria chamomilla and Lycopersicon esculentum. Also, the bacterial growth, biofilm formation, swimming motility and bacterial cell membrane of Xoo strain GZ 0003 were significantly affected by ZnO nanoparticle. Overall, zinc oxide nanoparticles are promising biocontrol agents that can be used to combat bacterial leaf blight diseases of rice.

Biogenic synthesis of silver nanoparticles (AgNPs) using plants has become a promising substitute to the conventional chemical synthesis method. In this study, we report low-cost, green synthesis of AgNPs using fresh fruit extract of Phyllanthus emblica. The biosynthesized AgNPs was confirmed and characterized by analysis of spectroscopy profile of the UV-visible and Energy dispersive spectrophotometer, Fourier transform infrared, X-ray diffraction pattern, and electron microscopy images examination. UV-visible spectra showed a surface resonance peak of 430 nm corresponding to the formation of AgNPs, and FTIR spectra confirmed the involvement of biological molecules in AgNPs synthesis. In spherical AgNPs, the particle size ranged from 19.8 to 92.8 nm and the average diameter was 39 nm. Synthesized nanoparticles at 20 μg/ml showed remarkable antimicrobial activity in vitro against the pathogen Acidovorax oryzae strain RS-2 of rice bacterial brown stripe, while 62.41% reduction in OD₆₀₀ value was observed compared to the control. Moreover, the inhibitory efficiency of AgNPs increased with the increase of incubation time. Furthermore, AgNPs not only disturbed biofilm formation and swarming ability but also increased the secretion of effector Hcp in strain RS-2, resulting from damage to the cell membrane, which was substantiated by TEM images and live/dead cell staining result. Overall, this study suggested that AgNPs can be an attractive and eco-friendly candidate to control rice bacterial disease.

The biosynthesis of silver nanoparticles (AgNPs) through the use of endophytic bacteria is a safe replacement for the chemical method. The study aimed to synthesize AgNPs using endophytic bacterium Bacillus siamensis strain C1, which was isolated from the medicinal plant Coriandrum sativum. The synthesized AgNPs with the size of 25 to 50 nm were further confirmed and characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy with EDS profile. The synthesized AgNPs at 20 μg mL⁻¹ showed a strong antibacterial effect against the pathogen of rice bacterial leaf blight and bacterial brown stripe, while an inhibition zone of 17.3 and 16.0 mm was observed for Xanthomonas oryzae pv. oryzae (Xoo) strain LND0005 and Acidovorax oryzae (Ao) strain RS-1, respectively. Furthermore, the synthesized AgNPs significantly inhibited bacterial growth, biofilm formation and swimming motility of Xoo strain LND0005 and Ao strain RS-1. In addition, the synthesized AgNPs significantly increased root length, shoot length, fresh weight and dry weight of rice seedlings compared to the control. Overall, this study suggests that AgNPs have the potential to protect rice plants from bacterial infection and plant growth promotion.

Nanoparticles are expected to play a vital role in the management of future plant diseases, and they are expected to provide an environmentally friendly alternative to traditional synthetic fungicides. In the present study, silver nanoparticles (AgNPs) were green synthesized through the mediation by using the endophytic bacterium Pseudomonas poae strain CO, which was isolated from garlic plants (Allium sativum). Following a confirmation analysis that used UV–Vis, we examined the in vitro antifungal activity of the biosynthesized AgNPs with the size of 19.8–44.9 nm, which showed strong inhibition in the mycelium growth, spore germination, the length of the germ tubes, and the mycotoxin production of the wheat Fusarium head blight pathogen Fusarium graminearum. Furthermore, the microscopic examination showed that the morphological of mycelia had deformities and collapsed when treated with AgNPs, causing DNA and proteins to leak outside cells. The biosynthesized AgNPs with strong antifungal activity were further characterized based on analyses of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, EDS profiles, and Fourier transform infrared spectroscopy. Overall, the results from this study clearly indicate that the biosynthesized AgNPs may have a great potential in protecting wheat from fungal infection.

Recently, the use of herbs in the agriculture and food industry has increased significantly. In particular, Rosmarinus officinalis L. extracts have been reported to have strong antibacterial properties, which depend on their chemical composition. The present study displayed a biological method for synthesis of magnesium oxide (MgO) nano-flowers. The nano-flowers are developed without using any catalyst agent. Aqueous Rosemary extract was used to synthesize MgO nano-flowers (MgONFs) in stirring conditions and temperature at 70°C for 4 h. The mixture solution was checked by UV-Vis spectrum to confirm the presence of nanoparticles. The MgO nano-flowers powder was further characterized in this study by the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. In addition, bacteriological tests indicated that MgO nano-flowers significantly inhibited bacterial growth, biofilm formation, and motility of Xanthomonas oryzae pv. oryzae, which is the causal agent of bacterial blight disease in rice. The electronic microscopic observation showed that bacterial cell death may be mainly due to destroy of cell integrity, resulting in leakage of intracellular content. As recommended, the use of Rosemary extract is an effective and green way to produce the MgO nano-flowers, which can be widely used in agricultural fields to suppress bacterial infection.

Bacterial stem and root rot disease of sweet potato caused by Dickeya dadantii recently broke out in major sweet potato planting areas in China and calls for effective approaches to control the pathogen and disease. Here, we developed a simple method for green synthesis of silver nanoparticles (AgNPs) using bacterial culture supernatants. AgNPs synthesized with the cell-free culture supernatant of a bacterium Pseudomonas rhodesiae displayed the characteristic surface plasmon resonance peak at 420–430 nm and as nanocrystallites in diameters of 20–100 nm determined by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. Functional groups associated with proteins in the culture supernatant may reduce silver ions and stabilize AgNPs. The AgNPs showed antibacterial activities against D. dadantii growth, swimming motility, biofilm formation, and maceration of sweet potato tubers whereas the culture supernatant of P. rhodesiae did not. AgNPs (12 µg∙ml⁻¹) and AgNO₃ (50 µg∙ml⁻¹) showed close antibacterial activities. The antibacterial activities increased with the increase of AgNP concentrations. The green-synthesized AgNPs can be used to control the soft rot disease by control of pathogen contamination of sweet potato seed tubers.