Preparation of Nanomaterial Wettable Powder Formulations of Antagonistic Bacteria from Phellodendron chinense and the Biological Control of Brown Leaf Spot Disease

Activity of Streptomyces globosus OPF-9 against the important pathogen Alternaria longipes and biocontrol mechanisms revealed by multi-omic analyses

Plant diseases caused by fungal pathogens represent main threats to the yield and quality of agricultural products, and Alternaria longipes is one of the most important pathogens in agricultural systems. Biological control is becoming increasingly prevalent in the management of plant diseases due to its environmental compatibility and sustainability. In the present study, a bacterial strain, designated as OPF-9, was shown to effectively inhibit the pathogen A. longipes, which was identified as Streptomyces globosus. The culture conditions for OPF-9 were optimized through a stepwise approach and the fermentation broth acquired displayed an excellent inhibitory activity against A. longipes in vitro and in vivo. Further investigations suggested that the fermentation broth exhibited strong stability under a range of adverse environmental conditions. To reveal the molecular bases of OPF-9 in inhibiting pathogens, the whole-genome sequencing and assembly were conducted on this strain. It showed that the genome size of OPF-9 was 7.668 Mb, containing a chromosome and two plasmids. Multiple clusters of secondary metabolite synthesis genes were identified by genome annotation analysis. In addition, the fermentation broth of strain OPF-9 was analyzed by LC-MS/MS non-target metabolomic assay and the activity of potential antifungal substances was determined. Among the five compounds evaluated, pyrogallol displayed the most pronounced inhibitory activity against A. longipes, which was found to effectively inhibit the mycelial growth of this pathogen. Overall, this study reported, for the first time, a strain of S. globosus that effectively inhibits A. longipes and revealed the underlying biocontrol mechanisms by genomic and metabolomic analyses.

Bacillus velezensis FX-6 suppresses the infection of Botrytis cinerea and increases the biomass of tomato plants

Botrytis cinerea causing tomato gray mold is a major cause of economic loss in tomato production. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control tomato grey mold disease. In this study, Bacillus velezensis FX-6 isolated from the rhizosphere of plants displayed significant inhibitory ability against B. cinerea and could promote tomato plant growth. FX-6 could effectively inhibit the growth of Botrytis cinerea mycelium in vitro and in vivo, and the inhibitory rate in vitro could reach 78.63%. According to morphological observations and phylogenetic trees based on sequences of the 16S rDNA and gyrA (DNA gyrase subunit A) genes, the strain FX-6 was identified as Bacillus velezensis. In addition, B. velezensis FX-6 showed antagonistic activity against seven phytopathogens, this indicated that FX-6 had broad-spectrum biocontrol activity. We also found that FX-6 fermentation broth had the strongest antagonistic activity against B. cinerea when the culture time was 72 hours, and the inhibition rate was 76.27%. The growth promotion test revealed that strain FX-6 significantly promoted tomato seed germination and seedling growth. Further deeply study on growth-promoting mechanism indicated that the FX-6 produced IAA and siderophore, and had ACC deaminase activity. The trait of significant biological control activity and growth promoting effect on tomato imply that B. velezensis FX-6 has the potential to be used as a biocontrol agent for tomato gray mold management.

Strategic nanoparticle-mediated plant disease resistance

Nanotechnology is a promising means for development of sustainable agriculture while the study of nanoparticle-mediated plant disease resistance is still in its primary stage. Nanotechnology has shown great promise in regulating: the content of secondary metabolites, inducing disease resistance genes, delivering hormones, delivering biomolecules (such as: nucleotides, proteins, and activators), and obtaining transgenic plants to resist plant diseases. In this review, we conclude its versatility and applicability in disease management strategies and diagnostics and as molecular tools. With the advent of new biotechnologies (e.g. de novo regeneration, CRISPR/Cas9, and GRF4-GIF1 fusion protein), we discuss the potential of nanoparticles as an optimal platform to deliver biomolecules to plants for genetic engineering. In order to ensure the safe use and social acceptance of plant nanoparticle technology, its adverse effects are discussed, including the risk of transferring nanoparticles through the food chain.

Bioinspired Green Synthesis of Silver Nanoparticles Using Three Plant Extracts and Their Antibacterial Activity against Rice Bacterial Leaf Blight Pathogen Xanthomonas oryzae pv. oryzae

Rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is responsible for a significant reduction in rice production. Due to the small impact on the environment, biogenic nanomaterials are regarded as a new type of antibacterial agent. In this research, three colloids of silver nanoparticles (AgNPs) were synthesized with different biological materials such as Arctium lappa fruit, Solanum melongena leaves, and Taraxacum mongolicum leaves, and called Al-AgNPs, Sm-AgNPs and Tm-AgNPs, respectively. The appearance of brown colloids and the UV-Visible spectroscopy analysis proved the successful synthesis of the three colloids of AgNPs. Moreover, FTIR and XRD analysis revealed the formation of AgNPs structure. The SEM and TEM analysis indicated that the average diameters of the three synthesized spherical AgNPs were 20.18 nm, 21.00 nm, and 40.08 nm, respectively. The three botanical AgNPs had the strongest bacteriostatic against Xoo strain C2 at 20 μg/mL with the inhibition zone of 16.5 mm, 14.5 mm, and 12.4 mm, while bacterial numbers in a liquid broth (measured by OD600) decreased by 72.10%, 68.19%, and 65.60%, respectively. Results showed that the three AgNPs could inhibit biofilm formation and swarming motility of Xoo. The ultrastructural observation showed that Al-AgNPs adhered to the surface of bacteria and broke the bacteria. Overall, the three synthetic AgNPs could be used to inhibit the pathogen Xoo of rice bacterial leaf blight.

Bacillus velezensis SYL-3 suppresses Alternaria alternata and tobacco mosaic virus infecting Nicotiana tabacum by regulating the phyllosphere microbial community

The occurrence of plant diseases is closely associated with the imbalance of plant tissue microecological environment. The regulation of the phyllosphere microbial communities has become a new and alternative approach to the biological control of foliar diseases. In this study, Bacillus velezensis SYL-3 isolated from Luzhou exhibited an effective inhibitory effect against Alternaria alternata and tobacco mosaic virus (TMV). The analysis of phyllosphere microbiome by PacBio sequencing indicated that SYL-3 treatment significantly altered fungal and bacterial communities on the leaves of Nicotiana tabacum plants and reduced the disease index caused by A. alternata and TMV. Specifically, the abundance of P. seudomo, Sphingomonas, Massilia, and Cladosporium in the SYL-3 treatment group increased by 19.00, 9.49, 3.34, and 12.29%, respectively, while the abundances of Pantoea, Enterobacter, Sampaiozyma, and Rachicladosporium were reduced. Moreover, the abundance of beneficial bacteria, such as Pseudomonas and Sphingomonas, was negatively correlated with the disease indexes of A. alternata and TMV. The PICRUSt data also predicted the composition of functional genes, with significant differences being apparent between SYL-3 and the control treatment group. Further functional analysis of the microbiome also showed that SYL-3 may induce host disease resistance by motivating host defense-related pathways. These results collectively indicate that SYL-3 may suppress disease progression caused by A. alternata or TMV by improving the microbial community composition on tobacco leaves.