(1) Background: Ralstonia solanacearum causes tomato bacterial wilt disease, one of the most serious tomato diseases. As the combination of Trichoderma virens (Tvien6) and Bacillus velezensis (X5) was more effective at controlling tomato bacterial wilt disease than a single agent, we investigated the synergistic effect of Tvien6 and X5 in controlling this disease; (2) Methods: The disease incidence, plant heights and weights, relative chlorophyll content (SPAD values), defensive enzymes (PPO, POD, and SOD) activities, and metabolome were estimated among four treatment groups (BR treatment, X5 + R. solanacearum (RS-15); TR treatment, Tvien6+ RS-15; TBR treatment, Tvien6 + X5 + RS-15; and R treatment, RS-15); (3) Results: The R treatment group had the highest disease incidence and lowest plant heights, plant weights, SPAD values, defensive enzyme activities, and D-fructose and D-glucose contents; the TBR treatment group had the lowest disease incidence and highest plant heights, plant weights, SPAD values, defensive enzyme activities, and D-fructose and D-glucose contents; (4) Conclusions: The results revealed that Tvien6 and X5 can both individually promote tomato plant growth, increase leaf chlorophyll content, enhance defensive enzyme activities, and induce the accumulation of D-fructose and D-glucose; however, they were more effective when combined.

Fusarium oxysporum f. sp. cubense (Foc) causes banana Fusarium wilt disease, which is a destructive soil-borne disease. Many plants can recruit rhizosphere microorganisms using their root exudates, thereby shaping the rhizosphere microbiome to resist pathogen infection. Therefore, this study was conducted to explore the role of root exudates in the process of biocontrol strain colonization and resistance to pathogens. In this study, the banana root exudates used as chemoattractants were obtained by hydroponics. Bacillus velezensis strain LG14-3 was isolated from the infected area of the root system of banana and showed significant chemotaxis to banana root exudates and strong inhibition of Fusarium oxysporum f. sp. cubense. Further analysis found that LG14-3 showed chemotaxis toward the components of banana root exudates, such as citric acid, succinic acid, glycine, D-galactose and D-maltose, and glycine and citric acid, which resulted in more significant chemotaxis of LG14-3. Moreover, banana root exudates enhanced the swarming motility and biofilm formation of LG14-3. Pot experiments showed that glycine and citric acid enhanced the colonization ability of Bacillus velezensis LG14-3 in the banana rhizosphere and reduced the disease severity index of banana fusarium wilt. Glycine and citric acid enhanced the growth-promoting ability of LG14-3 under pathogen stress. Our results showed that the addition of chemotactic substances enhanced the biocontrol potential of Bacillus velezensis LG14-3 to prevent banana Fusarium wilt.

Banana wilt disease is an important disease in banana production, causing significant losses. Herein, we investigated the mechanism by which Bacillus velezensis isolate X5 enhances the resistance of different resistant banana cultivars to Fusarium oxysporum f. sp. cubense race 4 (Foc4). From the perspectives of metabolism, transcriptome, and key genes in important pathways, this study analyzed the composition and content changes of other types of signaling molecules, such as free amino acids and soluble sugars, in resistant/susceptible varieties. The results indicate that under pathogen stress, the contents of root-secreted metabolite components in both resistant and susceptible varieties increase significantly overall, and the increase in susceptible varieties is generally higher. For example, the free amino acid components in susceptible varieties are significantly more than those in resistant varieties. However, the addition of biocontrol bacteria can inhibit this increase. Exogenous addition experiments prove that differential metabolites can either promote or inhibit Foc4 and X5 at certain concentrations. The results of KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment and GO (Gene Ontology) annotation show that resistant varieties have more defense pathways compared to susceptible varieties. Under X5 treatment, more defense genes in resistant varieties are activated or their expression is enhanced, promoting the plant roots to secrete more substances related to plant resistance, such as phenylpropanoids and lignin. This research revealed the effects of Bacillus velezensis on bananas and pathogens, allowing valuable conclusions to be drawn. The results have good application potential to understand the relationships among the three species, defining the biocontrol effect and mechanism of Bacillus velezensis, and providing a theoretical basis for the biological control of soil-borne diseases such as banana wilt disease.

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), severely impacts citrus production. This study developed a novel zinc oxide nanoparticles ROS-triggered generation system (ZnO NPs) as an effective bactericidal agent against Xcc. The ZnO NPs exhibited higher antibacterial activity than the commercially available pesticide zinc thiazole. The minimum inhibitory concentration (MIC) of ZnO NPs (104.5 μg/mL) is 7.42 times higher than that of 104.5 μg/mL zinc thiazole. Additionally, 1 MIC of ZnO NPs and 1 MIC of zinc thiazole (690.5 μg/mL) exhibited similar therapeutic efficiency, with disease incidences of 3.75 ± 2.04% and 3.33 ± 0.59%, respectively. As the concentration of ZnO NPs increased from 0 to 104.5 μg/mL, Xcc fluorescence density increased from 4377 ± 266.48 to 20,158.67 ± 3133.39 a.u. The ZnO NPs significantly reduced the activity of two key citrate cycle (TCA cycle) enzymes, malate dehydrogenase and succinate dehydrogenase, and disturbed multiple ROS-related metabolic pathways, such as TCA cycle, glutathione metabolism, and ABC transporters. Metabolites associated with ROS-scavenging and cell membrane synthesis, such as carnosine, biotin, valeric acid, and adrenic acid, were significantly downregulated. Pantothenate and CoA biosynthesis, tryptophan metabolism, arginine and proline metabolism, and arginine biosynthesis were identified as potential target pathways. These results suggest that the antibacterial activity of ZnO NPs is mediated by enhanced ROS accumulation, metabolic disruption, and cell membrane damage, leading to leakage of intracellular contents. Moreover, ZnO NPs enhanced citrus disease resistance. This study demonstrates the ZnO NPs as a promising antibacterial agent against Xcc and elucidates its antibacterial mechanisms.

摘要：土传病害严重危害农作物的生产，并显著降低作物产量和品质。传统病害三角模型聚焦于单一病原体与宿主、环境的关系，而基于高通量测序技术的微生物组学研究发现，植物微生物组作为植物的“第二基因组”，是直接影响植物养分吸收，响应非生物胁迫和病害成功侵染与否的关键因素之一。因此应将微生物组维度添加到由寄主植物、病原体和环境组成的经典“病害三角”中，形成“病害金字塔”。本文综述了“抑病土”研究的三种类型，植物基因型、土壤理化性质、农业措施、有益微生物及其药肥和其他环境因素对土传病害与微生物组互作的影响，以及微生物组-土传病害互作的“求救”和“反馈调节”机制，并从植物微生物组育种、微生物组数据机器学习和微生物群落开发利用及作用机制三方面进行了展望。文中强调了使用跨学科方法，开展利用微生物菌群减轻土传病害和提高作物生产力的重要性，为保护环境并促进可持续农业发展提供理论依据和技术支撑。