Phage combination alleviates bacterial leaf blight of rice (Oryza sativa L.)

Rice bacterial leaf blight (BLB) is the most destructive bacterial diseases caused by Xanthomonas oryzae pv. oryzae (Xoo). Phages have been proposed as a green and efficient strategy to kill bacterial pathogens in crops, however, the mechanism of action of phages in the control of phyllosphere bacterial diseases remain unclear. Here, the glasshouse pot experiment results showed that phage combination could reduce the disease index by up to 64.3%. High-throughput sequencing technology was used to analyze the characteristics of phyllosphere microbiome changes and the results showed that phage combinations restored the impact of pathogen invasion on phyllosphere communities to a certain extent, and increased the diversity of bacterial communities. In addition, the phage combination reduced the relative abundance of epiphytic and endophytic Xoo by 58.9% and 33.9%, respectively. In particular, Sphingomonas and Stenotrophomonas were more abundant. According to structural equation modeling, phage combination directly and indirectly affected the disease index by affecting pathogen Xoo biomass and phage resistance. In summary, phage combination could better decrease the disease index. These findings provide new insights into phage biological control of phyllosphere bacterial diseases, theoretical data support, and new ideas for agricultural green prevention and control of phyllosphere diseases

Bio-functionalized nickel-silica nanoparticles suppress bacterial leaf blight disease in rice (Oryza sativa L.)

IntroductionBacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most devastative diseases that threatens rice plants worldwide. Biosynthesized nanoparticle (NP) composite compounds have attracted attention as environmentally safe materials that possess antibacterial activity that could be used in managing plant diseases.MethodsDuring this study, a nanocomposite of two important elements, nickel and silicon, was biosynthesized using extraction of saffron stigmas (Crocus sativus L.). Characterization of obtained nickel-silicon dioxide (Ni-SiO2) nanocomposite was investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission/Scanning electron microscopy (TEM/SEM), and energy-dispersive spectrum (EDS). Antibacterial activities of the biosynthesized Ni-SiO2 nanocomposite against Xoo were tested by measuring bacterial growth, biofilm formation, and dead Xoo cells.Results and discussionsThe bacterial growth (OD600) and biofilm formation (OD570) of Xoo treated with distilled water (control) was found to be 1.21 and 1.11, respectively. Treatment with Ni-SiO2 NPs composite, respectively, reduced the growth and biofilm formation by 89.07% and 80.40% at 200 μg/ml. The impact of obtained Ni-SiO2 nanocomposite at a concentration of 200 μg/ml was assayed on infected rice plants. Treatment of rice seedlings with Ni-SiO2 NPs composite only had a plant height of 64.8 cm while seedlings treated with distilled water reached a height of 45.20 cm. Notably, Xoo-infected seedlings treated with Ni-SiO2 NPs composite had a plant height of 57.10 cm. Furthermore, Ni-SiO2 NPs composite sprayed on inoculated seedlings had a decrease in disease leaf area from 43.83% in non-treated infected seedlings to 13.06% in treated seedlings. The FTIR spectra of biosynthesized Ni-SiO2 nanocomposite using saffron stigma extract showed different bands at 3,406, 1,643, 1,103, 600, and 470 cm−1. No impurities were found in the synthesized composite. Spherically shaped NPs were observed by using TEM and SEM. EDS revealed that Ni-SiO2 nanoparticles (NPs) have 13.26% Ni, 29.62% Si, and 57.11% O. Xoo treated with 200 µg/ml of Ni-SiO2 NPs composite drastically increased the apoptosis of bacterial cells to 99.61% in comparison with 2.23% recorded for the control.ConclusionsThe application of Ni-SiO2 NPs significantly improved the vitality of rice plants and reduced the severity of BLB

The Green Synthesis of MgO Nano-Flowers Using Rosmarinus officinalis L. (Rosemary) and the Antibacterial Activities against Xanthomonas oryzae pv. oryzae

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

Role of the Genes of Type VI Secretion System in Virulence of Rice Bacterial Brown Stripe Pathogen Acidovorax avenae subsp. avenae Strain RS-2

The Type VI secretion system (T6SS) is a class of macromolecular machine that is required for the virulence of gram-negative bacteria. However, it is still not clear what the role of T6SS in the virulence of rice bacterial brown stripe pathogen Acidovorax avenae subsp. avenae (Aaa) is. The aim of the current study was to investigate the contribution of T6SS in Aaa strain RS2 virulence using insertional deletion mutation and complementation approaches. This strain produced weak virulence but contains a complete T6SS gene cluster based on a genome-wide analysis. Here we compared the virulence-related phenotypes between the wild-type (RS-2) and 25 T6SS mutants, which were constructed using homologous recombination methods. The mutation of 15 T6SS genes significantly reduced bacterial virulence and the secretion of Hcp protein. Additionally, the complemented 7 mutations ΔpppA, ΔclpB, Δhcp, ΔdotU, ΔicmF, ΔimpJ, and ΔimpM caused similar virulence characteristics as RS-2. Moreover, the mutant ΔpppA, ΔclpB, ΔicmF, ΔimpJ and ΔimpM genes caused by a 38.3~56.4% reduction in biofilm formation while the mutants ΔpppA, ΔclpB, ΔicmF and Δhcp resulted in a 37.5~44.6% reduction in motility. All together, these results demonstrate that T6SS play vital roles in the virulence of strain RS-2, which may be partially attributed to the reductions in Hcp secretion, biofilm formation and motility. However, differences in virulence between strain RS-1 and RS-2 suggest that other factors may also be involved in the virulence of Aaa

Biocontrol Efficacy of Endophyte <i>Pseudomonas poae</i> to Alleviate <i>Fusarium</i> Seedling Blight by Refining the Morpho-Physiological Attributes of Wheat

Some endophyte bacteria can improve plant growth and suppress plant diseases. However, little is known about the potential of endophytes bacteria to promote wheat growth and suppress the Fusarium seedling blight pathogen Fusarium graminearum. This study was conducted to isolate and identify endophytic bacteria and evaluate their efficacy for the plant growth promotion and disease suppression of Fusarium seedling blight (FSB) in wheat. The Pseudomonas poae strain CO showed strong antifungal activity in vitro and under greenhouse conditions against F. graminearum strain PH-1. The cell-free supernatants (CFSs) of P. poae strain CO were able to inhibit the mycelium growth, the number of colonies forming, spore germination, germ tube length, and the mycotoxin production of FSB with an inhibition rate of 87.00, 62.25, 51.33, 69.29, and 71.08%, respectively, with the highest concentration of CFSs. The results indicated that P. poae exhibited multifarious antifungal properties, such as the production of hydrolytic enzymes, siderophores, and lipopeptides. In addition, compared to untreated seeds, wheat plants treated with the strain showed significant growth rates, where root and shoot length increased by about 33% and the weight of fresh roots, fresh shoots, dry roots, and dry shoots by 50%. In addition, the strain produced high levels of indole-3-acetic acid, phosphate solubilization, and nitrogen fixation. Finally, the strain demonstrated strong antagonistic properties as well as a variety of plant growth-promoting properties. Thus, this result suggest that this strain could be used as an alternate to synthetic chemicals, which can serve as an effective method of protecting wheat from fungal infection

Improving agriculture and food security in Africa: Can the one health approach be the answer?

 The menace of food insecurity precipitated by climate change, zoonotic diseases and natural disasters poses a great threat to the sub-Saharan African region. Promoting food security and sustainable food systems is a priority for enhancing development in Africa. Holistic techniques such as one health approach recognises the linkages between the health of people, animals and the environment, and foster collaboration among various disciplines and stakeholders to address complex challenges. This review explored one health as a holistic approach in contributing to improved food security and sustainable food systems in African agriculture. Reviewed studies provided ample evidences demonstrating the robustness of one health approach as a multidisciplinary approach capable of increasing food production while enhancing health and environmental sustainability. The one health approach is not without challenges, however its capacity to encompass education and capacity building, policy formulation and execution, funding, advocacy and collaborations among multiple disciplines, makes it a veritable tool to improving food security and food systems in Africa. Achieving the balance between food production, food security, healthy living, and sustainable utilization of natural resources in providing for the existing population while preserving the benefits for future generations hinges on integrative actions such as one health approach.    </p