Rice sheath blight caused by Rhizoctonia solani is a devastating global rice disease. This study aimed to isolate biocontrol bacteria from the medicinal plant Bletilla striata for managing the disease. Strain A1 demonstrated the strongest antagonistic activity, with a 91.92% inhibition rate against R. solani in vitro. It also exhibited a broad antifungal spectrum against ten plant pathogenic fungi. Morphological and molecular (16S rRNA and recA genes) analysis identified strain A1 as Pseudomonas koreensis. In detached leaf assays, lesion length was significantly reduced. Pot and field trials showed control efficacies of 65.54% and 72.53%, respectively, comparable to the chemical agent Jinggangmycin. Strain A1 secreted extracellular enzymes (protease, β-1,3-glucanase), siderophores, and auxin (IAA), and possessed phosphate-solubilizing and nitrogen-fixing capabilities. The strain significantly enhanced the activities of key defense enzymes (POD, PAL, PPO, CAT, SOD) in rice. Furthermore, both its sterile culture filtrate and the corresponding crude ethyl acetate extract exhibited strong, direct suppression of R. solani growth. LC-MS analysis identified potential antifungal compounds, including Pseudomonic Acid, Artemisinin, and Tetradecane, in the extract. In conclusion, P. koreensis A1 is a promising biocontrol and plant growth-promoting candidate for sustainable management of rice sheath blight.

Successful seed germination and plant seedling growth often require association with endophytic bacteria. Barnyard grass (Echinochloa crus-galli (L.) P. Beauv.) is a main weed during rice cultivation and has frequently been found in drought-prone fields such as cornfields in recent years. To determine whether endophytic bacteria enhance the survival chances of barnyard grass in dryland conditions, endophytic bacteria were collected from barnyard grass seeds. An endophytic bacterial strain, BC-14, was selected and confirmed as Cronobacter dublinensis based on its morphology, physiology, biochemistry, and genomic information. Moreover, C. dublinensis BC-14 secreted IAA in the Luria–Bertani broth up to 28.44 mg/L after 5 days; it could colonize the roots of barnyard grass. After the inoculation with seeds or the well-mixed planting soil, the bacterium can significantly increase the root length and plant height of barnyard grass under drought conditions. When comparing with the control group on the 28th day, it can be seen that the bacterium can significantly increase the contents of chlorophyll b (up to 7.58 times) and proline (37.21%); improve the activities of superoxide dismutase, catalase, and peroxidase (36.90%, 51.51%, and 12.09%, respectively); and reduce the content of malondialdehyde around 25.92%, which are correlated to the drought tolerance. The bacterial genomic annotation revealed that it contains growth-promoting and drought-resistant functional genes. In a word, C. dublinensis BC-14 can help barnyard grass suppress drought stress, promote plant growth, and enhance biomass accumulation, which is helpful to interpret the mechanism of weed adaptability in dry environments.

The long-term application of traditional chemical herbicides has caused a significant escalation in herbicide resistance of barnyard grass (Echinochloa crus-galli). As an eco-friendly alternative, biological herbicides demonstrate substantial application potential. Acknowledging the growing herbicide resistance of E. crus-galli, this study aimed to screen target bacteria with inhibitory effects on the growth for bio-herbicide development. By using ungerminated E. crus-galli seeds as the screening substrate, a bacterial strain (BFYBC-8) with potent inhibitory activity was isolated and identified as Brucella pseudorignonensis. Pot experiments revealed that inoculation with B. pseudorignonensis BFYBC-8 significantly suppressed E. crus-galli growth, reducing plant height by 16.7% and root length by 85.1%, while markedly inhibiting biomass accumulation. Fluorescent labeling with green fluorescent protein (GFP) showed that BFYBC-8 successfully colonized the root intercellular spaces of E. crus-galli and extended continuously along the tissue matrix. Additionally, the strain’s supernatant metabolic products exhibited exceptional thermostability: inhibitory activity against E. crus-galli was maintained after thermal treatment at 28 °C, 60 °C, 80 °C, and 100 °C. Crucially, the bacterium displayed no toxicity to agronomically important crops such as rice, wheat, and corn. This study highlights B. pseudorignonensis BFYBC-8 as a promising candidate for bioherbicide development and provides an important reference for applying seed-associated pathogenic bacteria in developing bioherbicides for sustainable weed management.

Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum (Fon), severely restricts the sustainable development of the global watermelon industry. While conventional chemical fungicides of this disease have triggered prominent ecological issues, Bacillus-based microbial biocontrol, which combines inherent environmental compatibility with stable control efficacy, has emerged as a key green alternative to chemical management. However, the biocontrol potential of Bacillus sonorensis against this disease has not yet been fully investigated. In this study, we isolated 56 bacterial strains from healthy watermelon rhizosphere soil, and obtained a Fon-antagonistic strain A-5 with the strongest activity (70.15% mycelial inhibition rate), which was identified as B. sonorensis via polyphasic taxonomic analysis. In vitro assays showed that the sterile fermentation filtrate of strain A-5 had a maximum 81.05% inhibition rate against Fon, and its volatile organic compounds also significantly suppressed Fon growth, with broad-spectrum antifungal activity against four common phytopathogenic fungi. Functional tests confirmed that strain A-5 could secrete cell wall-degrading enzymes, produce siderophores and synthesize indole-3-acetic acid, and 17 antimicrobial secondary metabolite biosynthetic gene clusters were identified in its genome. Pot experiments verified that strain A-5 had a 78.04% relative control efficacy against watermelon Fusarium wilt, which significantly reduced seedling disease incidence and upregulated defense-related antioxidant enzyme activities in watermelon leaves. In general, B. sonorensis A-5 is a promising novel biocontrol agent for green management of watermelon Fusarium wilt.

Sclerotinia sclerotiorum causes destructive sclerotinia stem rot and severe yield losses in global rapeseed production. The Bacillus biocontrol strain YZUS007 serves as an eco-friendly alternative to synthetic fungicides, yet its control efficacy fluctuates under complex field conditions. This study aimed to investigate whether low-dose ZnO NPs could enhance the biocontrol efficacy of YZUS007 and to elucidate the underlying mechanisms. We isolated and identified the antagonistic strain Bacillus siamensis YZUS007 from the rhizosphere soil of healthy Brassica napus, which exhibited an in vitro pathogen inhibition rate of 78.4 ± 0.7%. Pot tests showed that YZUS007 (BC) achieved 60.79% control efficacy, whereas the YZUS007 + 20 μg/mL ZnO NPs group (BZ) reached 74.68%. Cell-free filtrate of YZUS007 (EC) had a 50.44% control efficacy, and filtrate with ZnO NPs (EZ) increased efficacy to 58.08%. LC-MS/MS identified four extracellular metabolites with increased relative abundances: cinnamic acid, sesamol, patchouli alcohol and 2-phenylbutyric acid. The combined treatment boosted defense enzyme activities and induced higher expression of the defense-related genes RBOH, PR1 and WRKY33. Collectively, low-concentration ZnO NPs significantly enhanced the biocontrol performance of YZUS007 by promoting antifungal metabolite accumulation, providing a low-dose, nanomaterial-assisted strategy for sustainable sclerotinia rot management.