Control Of Soil-borne Diseases Research Articles

Nonphytotoxic and pH-responsive ZnO-ZIF‑8 loaded with honokiol as a “nanoweapon” effectively controls the soil-borne bacterial pathogen Ralstonia solanacearum

The development of intelligently released and environmentally safe nanocarriers not only aligns with the sustainable agricultural strategy but also offers a potential solution for controlling severe soil-borne bacterial diseases. Herein, the core-shell structured nanocarrier loaded with honokiol bactericide (honokiol@ZnO-ZIF-8) was synthesized via a one-pot method for the targeted control of Ralstonia solanacearum, the causative agent of tobacco bacterial wilt disease. Results indicated that honokiol@ZnO-ZIF-8 nanoparticles induced bacterial cell membrane and DNA damage through the production of excessive reactive oxygen species (ROS), thereby reducing bacterial cell viability and ultimately leading to bacterial death. Additionally, the dissociation mechanism of the nanocarriers was elucidated for the first time through thermodynamic computational simulation. The nanocarriers dissociate primarily due to H+ attacking the N atom on imidazole, causing the rupture of the Zn-N bond under acidic conditions and at room temperature. Furthermore, honokiol@ZnO-ZIF-8 exhibited potent inhibitory effects against other prominent Solanaceae pathogenic bacteria (Pseudomonas syringae pv. tabaci), demonstrating its broad-spectrum antibacterial activity. Biosafety assessment results indicated that honokiol@ZnO-ZIF-8 exhibited non-phytotoxicity towards tobacco and tomato plants, with its predominant accumulation in the roots and no translocation to aboveground tissues within a short period. This study provides potential application value for the intelligent release of green pesticides. Environment implicationThe indiscriminate use of agrochemicals poses a significant threat to environmental, ecological security, and sustainable development. Slow-release pesticides offer a green and durable strategy for crop disease control. In this study, we developed a non-phytotoxic and pH-responsive honokiol@ZnO-ZIF-8 nano-bactericide based on the pathogenesis of Ralstonia solanacearum. Thermodynamic simulation revealed the dissociation mechanism of ZIF-8, with different acidity controlling the dissociation rate. This provides a theoretical basis for on-demand pesticide release while reducing residue in the. Our findings provide strong evidence for effective soil-borne bacterial disease control and on-demand pesticide release.

Enhancing soil properties, soil-borne diseases control, and quality through selecting high C/N agricultural waste during reductive soil disinfestation for continuous tobacco cropping

The addition of organic matter is crucial for achieving successful reductive soil disinfestation (RSD) for flue-cured tobacco cultivation. However, the effects of diverse organic materials and their application rates on soil-borne disease control and yield enhancement remain poorly understood. To address this, field experiments were conducted at two sites. Two organic materials, G and D, were employed with varying application rates (CK, G/D0.8, G/D1.0, and G/D1.2). The results demonstrated that adding these organic materials enhanced soil physicochemical properties, including pH, alkaline nitrogen, available phosphorus, available potassium, organic matter, and the C/N ratio. Furthermore, the relative abundance of Phytophthora nicotianae and Fusarium spp., with associated soil-borne diseases, was significantly reduced. Particularly, the G1.2 treatment exhibited a remarkable reduction in the relative abundance of the two pathogenic bacteria by over 20% at both experimental sites. Moreover, this treatment contributed to a reduction in disease incidence by over 21% and severity by over 72%. Increasing the application rates of these organic materials also enhanced nutrient content, agronomic traits, and biomass accumulation of flue-cured tobacco plants, improving the chemical composition of tobacco leaves and economic outcomes in cured-tobacco leaves. Notably, the G1.2 treatment at both experimental sites significantly enhanced the economic indices of tobacco leaves, respectively increasing the yield and output value by 10.6 kg ha−1 and 159.9 US$·ha−1. Overall, applying 15 t ha−1 (G1.2 treatment) of solid organic material during RSD was the optimal choice for sterilization, elimination of harmful substances, and enhancement of the economic characteristics of flue-cured tobacco.

Endophytic Streptomyces sp. NEAU-DD186 from Moss with Broad-Spectrum Antimicrobial Activity: Biocontrol Potential Against Soilborne Diseases and Bioactive Components.

Soilborne diseases cause significant economic losses in agricultural production around the world. They are difficult to control because a host plant is invaded by multiple pathogens, and chemical control often does not work well. In this study, we isolated and identified an endophytic Streptomyces sp. NEAU-DD186 from moss, which showed broad-spectrum antifungal activity against 17 soilborne phytopathogenic fungi, with Bipolaris sorokiniana being the most prominent. The strain also exhibited strong antibacterial activity against soilborne phytopathogenic bacteria Ralstonia solanacearum. To evaluate its biocontrol potential, the strain was prepared into biofertilizer by solid-state fermentation. Response surface methodology was employed to optimize the fermentation conditions for maximizing spore production and revealed that the 1:1 ratio of vermicompost to wheat bran, a temperature of 28°C, and 50% water content with an inoculation amount of 15% represented the optimal parameters. Pot experiments showed that the application of biofertilizer with a spore concentration of 108 CFU/g soil could effectively suppress the occurrence of tomato bacterial wilt caused by R. solanacearum and wheat root rot caused by B. sorokiniana, and the biocontrol efficacy was 81.2 and 72.2%, respectively. Chemical analysis of strain NEAU-DD186 extracts using nuclear magnetic resonance spectrometry and mass analysis indicated that 25-O-malonylguanidylfungin A and 23-O-malonylguanidylfungin A were the main active constituents, which showed high activity against R. solanacearum (EC50 of 2.46 and 2.58 µg ml-1) and B. sorokiniana (EC50 of 3.92 and 3.95 µg ml-1). In conclusion, this study demonstrates that Streptomyces sp. NEAU-DD186 can be developed as biofertilizer to control soilborne diseases.

Impact of phosphorus rate, soil fumigation, and cultivar on potato yield, quality, phosphorus use efficiency and economic returns in a high phosphorus soil

Phosphorus (P) is a non-renewable resource that will become an economic limiting factor for food production in the future. Potato (Solanum tuberosum L.) is a relatively shallow rooted crop and often responds positively to P fertilizer even in soils with high soil-test P. Therefore, high-rate P fertilizers are commonly applied to produce high tuber yields in commercial potato fields. The purpose of this study was to evaluate the effects of P rate, cultivar, and soil fumigation on potato yield, quality, P uptake, P use efficiency and economic returns under high soil test P conditions. A field study with a split-plot randomized complete block design was conducted in 2021 and 2022, with fumigation treatments (no fumigant or fall-applied metam sodium) being the main plots and cultivars (Ivory Russet or Russet Burbank) as subplots. Each subplot was further divided into five sub-subplots with different P rates: 0, 37, 73, 147 and 220 kg P ha-1. The results indicated that Russet Burbank produced higher total yield than Ivory Russet. Fumigation significantly increased tuber yield and dry matter percentage. Both cultivars responded to P application and tuber P uptake increased with P rate even under very high soil test P conditions. Both partial factor productivity (PFP) and P recovery efficiency (PRE) were very low and significantly decreased with the P rate. Russet Burbank had higher PFP and PRE than Ivory Russet, and fumigated plots had significantly higher PRE than non-fumigated plots. The tuber yield output and net revenue of Russet Burbank was higher than Ivory Russet, and the highest economic return was obtained in fumigated plots at 147 kg P ha-1. These results suggest that cultivar selection and control of soil-borne diseases should be considered to optimize P input, tuber yield, and to conserve P resources.

Role of Soil Management in Control of Soil-Borne Diseases

Role of Soil Management in Control of Soil-Borne Diseases

Investigating the effectiveness of ginger and turmeric extracts on common soil-borne pathogens affecting plants

Soil-borne viruses have crop production across the world, resulting in lower crop yields, poor crop performance, and rising production costs. Crop production has faced increased threats in recent years, including soil-borne disease epidemics, high chemical fungicide costs and the development of fungicide resistance, climate change, new disease outbreaks, and growing concern for both environmental and soil health. To address these infections, crop producers must implement integrated soil-borne disease control measures. In this work, two plant extracts (ginger and turmeric) were examined in vitro and in vivo for their ability to inhibit soil-borne pathogen mycelia development. Turmeric effectively suppressed the development of two pathogens when added to the two extracted extracts, with 74.59% inhibition against Fusarium sp and 73.49% inhibition against Rhizoctonia sp. Ginger extracts demonstrated a somewhat lower inhibitory activity against Rhizoctonia, with 73.58% inhibition at 50% concentration and 72.15% at 50% concentration. In vivo tests of turmeric extract against Rhizoctonia solani and Fusarium sp. were carried out to further the research. The data showed that using turmeric extract resulted in a substantial reduction in illness severity and incidence in both infections.

Polyacrylamide quaternary ammonium salts based on stable adsorption in soil and its application on the control of soil-borne fungal disease

Currently, soil-borne fungal disease (SBFD) have caused a huge damage in agriculture, and small molecule soil disinfectants have been widely used for the prevention and control of SBFD, which could not only kill the chlamydospore of pathogenic fungi, but also completely destroy the microbial community and its functional diversity in the soil, and is not conducive to subsequent plant planting. Therefore, how to effectively inhibit plant pathogenic fungi while maintaining the general balance of microbial population in the soil to facilitate subsequent plant planting come to be critical problem in the prevention and control of SBFD. In this work, a series of polyacrylamide containing quaternary ammonium salts (PAM-X) were synthesized based on the radical copolymerization of acrylamide (AM) and acrylamide containing different quaternary ammonium salts groups (AMX). Owing to the entanglement between polymer chains and soil, PAM-X could be stably absorbed in the soil, thus effectively delaying the free migration of PAM-X chains in soil, and reducing the probability of being leached from soil, which might be the key to obtain novel polymeric quaternary ammonium salts that have less impact on the environment. Banana Fusarium wilt, also known as “banana cancer”, caused by Fusarium oxysporum f. sp. cubense (Foc), was chosen as a typical soil-borne pathogen disease to verify the rationality of the above thoughts. The results showed PAM-X had well anti-Foc4 activities in soil, and could maintain the general balance of microbial population in the soil, which are almost non-toxic to earthworms in soil and fish, thus provides a new prevention and control method for SBFD.

Identification of metabolites generated in the biotransformation process by the Danio rerio (zebrafish) exposed to the fungicide tebuconazole

Tebuconazole is a triazole fungicide widely used in agricultural crops for control of multiple fungal, mainly foliar and soil-borne diseases. Due to its intense use, this pesticide has been detected on aquatic matrices in different countries, which makes it necessary to identify metabolites capable to be used in its exposure monitoring. The aim of this work was to evaluate tebuconazole metabolites in zebrafish water tanks using liquid chromatography coupled to a high-resolution mass spectrometer (LCHRMS) to highlight analytical targets to monitor tebuconazole exposure in aquatic environments. Two Phase I metabolites, TEB-OH and TEB-COOH, and one Phase II metabolite, TEB-S, were identified. Target metabolomics pointed TEB-S as the most important metabolite for discrimination between treatment and negative control group and potential surrogate for detection and monitoring of tebuconazole exposure in aquatic environments. To the best of our knowledge, this is the first study to suggest the sulphation of tebuconazole (TEB-S) by zebrafish metabolism. Moreover, the use of water samples proved to be a promising approach when compared to the usual biological matrices (e.g. plasma) for evaluating the exposure of aquatic animals to tebuconazole because it is a clean and easy to obtain matrix. Water samples presented a higher concentration of metabolites when compared to plasma samples. The results suggest the applicability of this assay model for the identification of potential biomarkers for monitoring the presence of xenobiotics in water.

Biotic and abiotic responses to soilborne pathogens and environmental predictors of soil health

Soilborne pathogens affect agricultural productivity and soil functions, yet the specific impacts of pathogen infections on the soil and plant root-associated microbiomes, the key determinants of plant health, remain unclear. Filling this knowledge gap is required to understanding microbial ecological responses, and to developing biological tools to manage and predict the prevalence and severity of soilborne diseases, which can improve soil health, and plant yield. We hypothesized that soilborne pathogens impact the diversity, function, and ecological interactions in soil microbiomes and form a pathobiome. To test the hypothesis, we conducted field sampling in 35 cotton fields in Australia and collected a total of 560 soil samples, which included samples from the rhizosphere (the area in close contact with the roots) and bulk soils. We aimed to investigate how soil microbiomes and key soil properties respond to Verticillium wilt (VW) of cotton, which is caused by the soilborne pathogen Verticillium dahliae. We found that the presence of the pathogen altered the microbiome structure in both bulk and rhizosphere soils. Notably, healthy soils exhibited more complex microbial networks than diseased soils. Furthermore, a putative pathobiome consisting of various microbial taxa that could influence pathogen infection was identified. Specific pathobiome taxa, such as Gibellulopsis spp., displayed a positive association with V. dahliae. In contrast, known biocontrol agents (BCAs) such as Bacillus spp., Fusarium spp., and Talaromyces spp., were negatively correlated with pathogen abundance. After isolation, pathobiome BCA members demonstrated strong biocontrol activity against V. dahliae in vitro, indicating their potential for enhancing resistance to pathogen invasion in agricultural soils. Moreover, shotgun sequencing analysis revealed a gene encoding beta-glucosidase as a putative indicator of soil health. Structural Equation Modelling showed that VW disease incidence is significantly influenced by several factors, including the relative abundance of V. dahliae, the pathobiome, and various abiotic factors such as precipitation, soil moisture, and pH. Taken together, our findings offer novel field evidence for the key biotic and abiotic drivers of a soilborne pathogen. This knowledge could facilitate the development of biological tools to control soilborne diseases and predict soil health and disease incidence, thus providing innovative strategies for sustainable agricultural disease management.

Multi-species endophytic Bacillus for improved control of potato soilborne and tuber-borne diseases in Tunisia: from laboratory to field conditions

BackgroundDue to the soilborne and tuber-borne nature of their causative agents, Fusarium wilt, Rhizoctonia root canker and black dot diseases are still leading to serious problems in potato production in Tunisia and worldwide. Among endophytic bacteria, the genus Bacillus is one of the most exploited microbial groups known as potent biocontrol agents against several potato diseases. In the present study, six strains belonging to five Bacillus species were screened for their abilities to inhibit root and wilt potato pathogens in vitro, in vivo and under natural conditions over three cropping seasons and to promote plant growth.ResultsBased on the dual-culture assays, the whole-cell suspensions of SV39 and SV104 (Bacillus tequilensis), SV41 (B. subtilis), SV44 (B. methylotrophicus) and SV65 (B. amyloliquefaciens subsp. plantarum) strains exhibited potent antifungal activity against important potato soilborne phytopathogens with ~ 65 to 70% inhibition rates. Significant inhibition rates were also induced by the cell-free culture filtrates, the butanolic and the chloroformic extracts depending on the target pathogens, the concentration used and the Bacillus strain tested. In pot experiment, a decrease in Rhizoctonia root canker severity, ranging from 43 to 65% compared to the inoculated and untreated control, was induced by all Bacillus spp. strain-based treatments, while SV39-, S42- and SV65-based treatments were the most effective in suppressing by 50–53 and 65–52%, black dot severity and the relative vascular discoloration extent induced by F. oxysporum f. sp. tuberosi, respectively, relative to positive control. This biocontrol potential was associated with an enhancement of potato growth parameters. Field studies indicated that soil treatment with the most of the Bacillus spp. strains had significantly controlled all the target fungal soilborne diseases and improved at the least two growth and/or production parameters depending on the strain used and the cropping seasons. SV39-, SV41-, SV44- and SV104-based treatments resulted in a significant increase in tuber yield in one cropping season.ConclusionThese Bacillus spp. strains could be used in combinations and/or introduced with other existing practices in order to provide supplemental control of target diseases and yield promotion under organic or conventional potato production systems.

A review of the efficacy of biofumigation agents in the control of soil-borne plant diseases

A review of the efficacy of biofumigation agents in the control of soil-borne plant diseases

Artificial Light for Improving Tomato Recovery Following Grafting: Transcriptome and Physiological Analyses.

Grafting is widely used to enhance the phenotypic traits of tomatoes, alleviate biotic and abiotic stresses, and control soil-borne diseases of the scion in greenhouse production. There are many factors that affect the healing and acclimatization stages of seedlings after grafting. However, the role of light has rarely been studied. In this study, we compared the effects of artificial light and traditional shading (under shaded plastic-covered tunnels) on the recovery of grafted tomato seedlings. The results show that the grafted tomato seedlings recovered using artificial light had a higher healthy index, leaf chlorophyll content, shoot dry weight, and net photosynthetic rate (Pn) and water use efficiency (WUE) compared with grafted seedling recovered using the traditional shading method. Transcriptome analysis showed that the differentially expressed genes (DEGs) of grafted seedlings restored using artificial light were mainly enriched in the pathways corresponding to plant hormone signal transduction. In addition, we measured the endogenous hormone content of grafted tomato seedlings. The results show that the contents of salicylic acid (SA) and kinetin (Kin) were significantly increased, and the contents of indoleacetic acid (IAA) and jasmonic acid (JA) were decreased in artificial-light-restored grafted tomato seedlings compared with those under shading treatments. Therefore, we suggest that artificial light affects the morphogenesis and photosynthetic efficiency of grafted tomato seedlings, and it can improve the performance of tomato seedlings during grafting recovery by regulating endogenous hormone levels.

Characterization of rhizosphere Pseudomonas chlororaphis IRHB3 in the reduction of Fusarium root rot and promotion of soybean growth

Rhizosphere beneficial bacteria play an important role in plant health and disease control, and have been widely explored as biocontrol resources and agents for the ecological and sustainable management of soil-borne diseases. In our previous study, a bacterium strain IRHB3 was isolated from soybean rhizosphere under maize-soybean relay strip intercropping. To clarify the characterization of IRHB3 and its biocontrol effects of soybean root rot, we systemically investigated the taxonomy, biological characteristics, bacteriostatic activity, environmental stress tolerance of IRHB3, and also analyzed its effects on the control of root rot as well as growth promotion. Our results showed that IRHB3 as a Gram-negative bacterium was identified as Pseudomonas chlororaphis by multi-locus sequence analysis of 16S rRNA, gyrB, rpoD and gapA. The colony was characterized by yellowish circular and rugby-shaped with rough surface and gullies under scanning electron microscropy.. IRHB3 not only activated kinds of hydrolase such as protease, caseinase, and cellulase, but was also capable of dissolving phosphorus, releasing siderophores and producing IAA. IRHB3 suspension treatment with proper concentration significantly promoted seed germination and seedling growth. Antagonistic assay showed that IRHB3 displayed good inhibition effects on various pathogenic fungi, especially aggressive Fusarium species causing root rot, with the average inhibition rate as high as 69.89%. And meanwhile, introducing IRHB3 into soil effectively alleviated the damage of F. oxysporum to soybean root. Moreover, IRHB3 had strong environmental adaptability of wide pH, low nutrition and salt stress. In conclusion, these results indicate that Pseudomonas chlororaphis IRHB3 from intercropped soybean rhizosphere is one kind of typically plant growth-promoting rhizobacteria (PGPR) and has immense potential and strong environmental adapatability on the control of soil-borne fungal disease.

Endophytic Streptomyces sp. NEAU-ZSY13 from the leaf of Perilla frutescens, as a promising broad-spectrum biocontrol agent against soil-borne diseases.

Soil-borne diseases cause significant economic losses in global agricultural production. These diseases are challenging to control due to the invasion of multiple pathogens into host plants, and traditional chemical control methods often yield unsatisfactory results. In this study, we isolated and identified an endophytic Streptomyces, designated as NEAU-ZSY13, from the leaf of Perilla frutescens. This isolate exhibited broad-spectrum antifungal activity against 17 soil-borne phytopathogenic fungi, with Bipolaris sorokiniana being the most prominent. Additionally, it displayed strong antibacterial activity against the soil-borne phytopathogenic bacterium Ralstonia solanacearum. To assess its biocontrol potential, the isolate was utilized to produce a biofertilizer through solid-state fermentation. The fermentation conditions were optimized using response surface methodology to maximize the spore production. The results revealed that more abundant spores were produced with a 1:2 ratio of vermicompost to wheat bran, 60% water content, 20% inoculation amount and 28°C. Subsequent pot experiments demonstrated that the application of the biofertilizer with a spore concentration of 108 CFU/g soil effectively suppressed the occurrence of tomato bacterial wilt caused by R. solanacearum and wheat root rot caused by B. sorokiniana, with biocontrol efficacies of 72.2 and 78.3%, respectively. Chemical analysis of NEAU-ZSY13 extracts, using nuclear magnetic resonance spectrometry and mass analysis, identified niphimycin C and niphimycin A as the primary active constituents. These compounds exhibited high activity against R. solanacearum (EC50 of 3.6 and 2.4 μg mL-1) and B. sorokiniana (EC50 of 3.9 and 3.4 μg mL-1). In conclusion, this study demonstrates the potential of Streptomyces sp. NEAU-ZSY13 as a biofertilizer for the control of soil-borne diseases.

Whole-genome analysis of the benzoic acid-degrading bacterium Bacillus halotolerans B28 to reveal its phytoprobiotic effects

Benzoic acid is a representative allelochemical in soils affected by continuous cropping obstacles, and it is also a typical aromatic pollutant, causing a direct or indirect inhibition on crop growth. In this study, a strain B28 that was isolated from the rhizosphere of peanut by using benzoic acid as the sole carbon source and sequenced. Strain B28 contained a single circular chromosome, the complete genome size was 4,132,583 bp, the average GC was 43.89%, with 3928 predicted genes, and based on phylogenomic analyses, B28 was designated as Bacillus halotolerans. The strain B28 with outstanding abilities to biodegrade benzoic acid, enhance plant growth and control soil-borne diseases, which were the key to the phytoprobiotic functions. Genome mining revealed the potential genomic properties associated with plant growth promotion, such as aromatic xenobiotics biodegradation, IAA synthesis, biofilm formation, chemotaxis motility and secondary metabolite synthesis. The effects of strain B28 on the growth of Arachis hypogaea L. (peanut) was evaluated, and the physiological parameters of peanut such as fresh weight, dry weight, plant height and root length were significantly higher after inoculating strain B28. Overall, our present results indicate that Bacillus halotolerans B28 is a potential PGPR strain for benzoic acid bioremediation and organic agriculture application.

Tapping the rhizosphere metabolites for the prebiotic control of soil-borne bacterial wilt disease

Prebiotics are compounds that selectively stimulate the growth and activity of beneficial microorganisms. The use of prebiotics is a well-established strategy for managing human gut health. This concept can also be extended to plants where plant rhizosphere microbiomes can improve the nutrient acquisition and disease resistance. However, we lack effective strategies for choosing metabolites to elicit the desired impacts on plant health. In this study, we target the rhizosphere of tomato (Solanum lycopersicum) suffering from wilt disease (caused by Ralstonia solanacearum) as source for potential prebiotic metabolites. We identify metabolites (ribose, lactic acid, xylose, mannose, maltose, gluconolactone, and ribitol) exclusively used by soil commensal bacteria (not positively correlated with R. solanacearum) but not efficiently used by the pathogen in vitro. Metabolites application in the soil with 1 µmol g−1 soil effectively protects tomato and other Solanaceae crops, pepper (Capsicum annuum) and eggplant (Solanum melongena), from pathogen invasion. After adding prebiotics, the rhizosphere soil microbiome exhibits enrichment of pathways related to carbon metabolism and autotoxin degradation, which were driven by commensal microbes. Collectively, we propose a novel pathway for mining metabolites from the rhizosphere soil and their use as prebiotics to help control soil-borne bacterial wilt diseases.

Microbial interactions within beneficial consortia promote soil health

By ecologically interacting with various biotic and abiotic agents acting in soil ecosystems, highly diverse soil microorganisms establish complex and stable assemblages and survive in a community context in natural settings. Besides facilitating soil microbiome to maintain great levels of population homeostasis, such microbial interactions drive soil microbes to function as the major engine of terrestrial biogeochemical cycling. It is verified that the regulative effect of microbe–microbe interplay plays an instrumental role in microbial-mediated promotion of soil health, including bioremediation of soil pollutants and biocontrol of soil-borne phytopathogens, which is considered an environmentally friendly strategy for ensuring the healthy condition of soils. Specifically, in microbial consortia, it has been proven that microorganism–microorganism interactions are involved in enhancing the soil health-promoting effectiveness (i.e., efficacies of pollution reduction and disease inhibition) of the beneficial microbes, here defined as soil health-promoting agents. These microbial interactions can positively regulate the soil health-enhancing effect by supporting those soil health-promoting agents utilized in combination, as multi-strain soil health-promoting agents, to overcome three main obstacles: inadequate soil colonization, insufficient soil contaminant eradication and inefficient soil-borne pathogen suppression, all of which can restrict their probiotic functionality. Yet the mechanisms underlying such beneficial interaction-related adjustments and how to efficiently assemble soil health-enhancing consortia with the guidance of microbe–microbe communications remain incompletely understood. In this review, we focus on bacterial and fungal soil health-promoting agents to summarize current research progress on the utilization of multi-strain soil health-promoting agents in the control of soil pollution and soil-borne plant diseases. We discuss potential microbial interaction-relevant mechanisms deployed by the probiotic microorganisms to upgrade their functions in managing soil health. We emphasize the interplay-related factors that should be taken into account when building soil health-promoting consortia, and propose a workflow for assembling them by employing a reductionist synthetic community approach.

Resistance to Fusarium oxysporum f. sp. luffae in Luffa Germplasm Despite Hypocotyl Colonization.

Fusarium wilt of Luffa, caused by Fusarium oxysporum f. sp. luffae (Folu), causes great losses in Luffa plants worldwide. In this study, 45 accessions of Luffa germplasm were used to determine their resistance to Folu isolates (FOLUST, FOLUSC, Fomh16, and Fol114) in two independent trials. In the first trial, only FOLUST was used to preliminarily identify resistant accessions. Nine accessions of L. acutangular and five of L. aegyptiaca were resistant to the FOLUST isolate. In the second trial, the other three isolates were then used to reevaluate the 14 resistant accessions. The results indicated that the 14 accessions were resistant to FOLUSC but exhibited variable resistance to the Fomh16 and Fol114 isolates. Eight accessions of L. acutangula and one accession of L. aegyptiaca were resistant to Fol114. Seven accessions of L. acutangula and one accession of L. aegyptiaca were resistant to Fomh16. Despite the lack of any symptoms, the Folu isolates were recovered from the hypocotyls of all resistant accessions at 28 days post inoculation, except for isolates FOLUSC and FOLUST on one accession (LA140). A high percentage (87.5%) of accessions collected from Bangladesh were identified as resistant, highlighting the effect of local adaptation on resistance. These results provide potentially valuable genetic resources for breeding programs to develop new varieties or rootstocks that could be beneficial for controlling soil-borne diseases in different cucurbit crops and further investigating the mechanisms of resistance to Folu in Luffa plants.

Bacillus velezensis RC116 Inhibits the Pathogens of Bacterial Wilt and Fusarium Wilt in Tomato with Multiple Biocontrol Traits.

Soil-borne plant diseases seriously threaten the tomato industry worldwide. Currently, eco-friendly biocontrol strategies have been increasingly considered as effective approaches to control the incidence of disease. In this study, we identified bacteria that could be used as biocontrol agents to mitigate the growth and spread of the pathogens causing economically significant diseases of tomato plants, such as tomato bacterial wilt and tomato Fusarium wilt. Specifically, we isolated a strain of Bacillus velezensis (RC116) from tomato rhizosphere soil in Guangdong Province, China, with high biocontrol potential and confirmed its identity using both morphological and molecular approaches. RC116 not only produced protease, amylase, lipase, and siderophores but also secreted indoleacetic acid, and dissolved organophosphorus in vivo. Moreover, 12 Bacillus biocontrol maker genes associated with antibiotics biosynthesis could be amplified in the RC116 genome. Extracellular secreted proteins of RC116 also exhibited strong lytic activity against Ralstonia solanacearum and Fusarium oxysporum f. sp. Lycopersici. Pot experiments showed that the biocontrol efficacy of RC116 against tomato bacteria wilt was 81%, and consequently, RC116 significantly promoted the growth of tomato plantlets. Based on these multiple biocontrol traits, RC116 is expected to be developed into a broad-spectrum biocontrol agent. Although several previous studies have examined the utility of B. velezensis for the control of fungal diseases, few studies to date have evaluated the utility of B. velezensis for the control of bacterial diseases. Our study fills this research gap. Collectively, our findings provide new insights that will aid the control of soil-borne diseases, as well as future studies of B. velezensis strains.

Soil Suppressiveness Against Pythium ultimum and Rhizoctonia solani in Two Land Management Systems and Eleven Soil Health Treatments.

The soil microbiome is known to be crucial for the control of soil-borne plant diseases. However, there is still little knowledge on how to modify the soil microbiome to induce or increase disease suppressiveness. In the present study, we applied eleven soil health treatments combined with conventional and organic agricultural management in a long-term field experiment. Suppressiveness against Pythium ultimum and Rhizoctonia solani was assessed in bioassays for 2 years. In addition, the microbiome community composition and microbial abundance were determined. We found that while several treatments changed the microbial community composition compared to the control, only a combination treatment of anaerobic soil disinfestation, hair meal, and compost addition resulted in suppressiveness against P. ultimum. Pythium suppressiveness is likely to have been caused by an increased microbial abundance and activity. Moreover, the increased abundance of several bacterial taxa, such as Pseudomonas sp., Chryseobacterium sp., members of the family Chitinophagaceae, and the fungal genus Mortierella sp. and family Trichosporonaceae, was measured. There was no overall difference in suppressiveness between conventional and organic land management. Also, no suppressiveness against R. solani could be detected. Our results indicate that a treatment combining the reduction of microorganisms followed by a recovery phase with high amounts of organic amendments may be more effective in inducing suppressiveness than treatments consisting of only one of these measures.