Previous studies have described the development of control methods against bacterial wilt diseases caused by Ralstonia solanacearum. This review focused on recent advances in control measures, such as biological, physical, chemical, cultural, and integral measures, as well as biocontrol efficacy and suppression mechanisms. Biological control agents (BCAs) have been dominated by bacteria (90%) and fungi (10%). Avirulent strains of R. solanacearum, Pseudomonas spp., Bacillus spp., and Streptomyces spp. are well-known BCAs. New or uncommon BCAs have also been identified such as Acinetobacter sp., Burkholderia sp., and Paenibacillus sp. Inoculation methods for BCAs affect biocontrol efficacy, such as pouring or drenching soil, dipping of roots, and seed coatings. The amendment of different organic matter, such as plant residue, animal waste, and simple organic compounds, have frequently been reported to suppress bacterial wilt diseases. The combined application of BCAs and their substrates was shown to more effectively suppress bacterial wilt in the tomato. Suppression mechanisms are typically attributed to the antibacterial metabolites produced by BCAs or those present in natural products; however, the number of studies related to host resistance to the pathogen is increasing. Enhanced/modified soil microbial communities are also indirectly involved in disease suppression. New promising types of control measures include biological soil disinfection using substrates that release volatile compounds. This review described recent advances in different control measures. We focused on the importance of integrated pest management (IPM) for bacterial wilt diseases.

https://www.jstage.jst.go.jp/article/jsme2/advpub/0/advpub_ME14144/_pdf

Recent trends in control methods for bacterial wilt diseases caused by Ralstonia solanacearum

Soil microbes play important roles in plant growth and health. Little is known about the differences of soil microbes between healthy and bacterial wilt infected soils with Ralstonia solanacearum. By Illumina-MiSeq sequencing of 16S rRNA and 18S rRNA gene amplicons, we found the soil microbial composition and diversity were distinct between healthy and bacterial wilt infected soils. Soil microbial community varied at different plant growth stages due to changes of root exudates composition and soil pH. Healthy soils exhibited higher microbial diversity than the bacterial wilt infected soils. More abundant beneficial microbes including Bacillus, Agromyces, Micromonospora, Pseudonocardia, Acremonium, Lysobacter, Mesorhizobium, Microvirga, Bradyrhizobium, Acremonium and Chaetomium were found in the healthy soils rather than the bacterial wilt infected soils. Compared to bacterial wilt infected soils, the activities of catalase, invertase and urease, as well as soil pH, available phosphorous and potassium content, were all significantly increased in the healthy soils. In a conclusion, the higher abundance of beneficial microbes are positively related the higher soil quality, including better plant growth, lower disease incidence, and higher nutrient contents, soil enzyme activities and soil pH.

/pdf/microbial-community-composition-is-related-to-soil-3oq7zhwkh0.pdf

Microbial community composition is related to soil biological and chemical properties and bacterial wilt outbreak.

Summary
Healthy soils that contain an active microbiome and food web are critical to sustainably produce food for a growing global human population. Many studies have focussed on the role of microbial species diversity and the presence of key functional groups as important controls on the many functions that a sustainable food system relies on.
Here, we synthesise recent ecological empirical evidence and theory to propose that the interactions between organisms in the soil food web are the critical determinant of soil function.
We propose the Rhizosphere Interactions for Sustainable Agriculture Model, in which crop roots recruit small, modular, highly connected soil rhizosphere networks from large, static, relatively unconnected and diverse bulk soil networks. We argue that conventional agricultural management disrupts the connections between rhizosphere and bulk soil networks.
Synthesis. We identify future research directions for optimising ecological connections between roots and rhizosphere microbial and faunal networks, and between rhizosphere networks and bulk soil networks in agricultural production systems. Knowledge on these connections can be applied in agricultural systems to sustainability produce food for a growing global population.

/pdf/below-ground-connections-underlying-above-ground-food-17uc1vosm8.pdf

Below-ground connections underlying above-ground food production: a framework for optimising ecological connections in the rhizosphere

Agricultural waste recycling in horticultural intensive farming systems by on-farm composting and compost-based tea application improves soil quality and plant health: A review under the perspective of a circular economy.

Root exudates play an important role in ecosystem response to climate change, but the functional consequences of drought‐induced changes in the quality of root exudates are unknown. Here, we addressed this knowledge gap in a unique experimental approach. We subjected two common grassland species that differ widely in their growth strategies and root systems, the grass Holcus lanatus and the forb Rumex acetosa, to 2 wk of drought. We collected root exudates and soils at the end of the drought and after 2 wk of recovery and readded all root exudates to all soils in a fully reciprocal set‐up to measure root‐exudate‐induced respiration. We found that soil treatment was unimportant for determining root‐exudate‐induced respiration. By contrast, root exudates collected from plants that had experienced drought clearly triggered more soil respiration than exudates from undroughted plants. Importantly, this increased respiration compensated for the lower rates of root exudation in droughted plants. Our findings reveal a novel mechanism through which drought can continue to affect ecosystem carbon cycling, and a potential plant strategy to facilitate regrowth through stimulating microbial activity. These findings have important implications for understanding plant and ecosystem response to drought.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.16001

Changes in root-exudate-induced respiration reveal a novel mechanism through which drought affects ecosystem carbon cycling.

Bacterial wilt caused by Ralstonia solanacearum is one of the most serious tobacco diseases worldwide. Brevibacillus brevis (L-25) and Streptomyces rochei (L-9) with strong inhibitory effects on R. solanacearum in vitro were isolated from the rhizosphere of a healthy tobacco plant in a severely wilt-diseased field. Pot and field experiments were conducted to evaluate the biocontrol effect of the isolated antagonists alone and in combination with organic fertilizer. In pot experiment, the control efficacy was 92.3–100 % in the treatments applied with L-25 and L-9 alone or together with organic fertilizers. When bioorganic fertilizer containing L-9 and L-25 was applied to the soil in field condition, the control efficacies were 95.4 and 30.0 in the Anhui and Guizhou field plots, respectively. The counts of bacteria and actinomycetes in rhizosphere soil were significantly increased (p ≤ 0.05) under all antagonist applications compared with CK (PR). In contrast, fungal and R. solanacearum densities in the rhizosphere soil applied with antagonists were much lower than the CK (PR) rhizosphere. Combined application of the two antagonists had better effect than single antagonist treatments. The antagonists were more effective when they were combined with organic fertilizer as compared with the antagonistic strains only. These results allow us to conclude that a combination of the biocontrol agents, L-25 and L-9, together with organic fertilizers can effectively control bacterial wilt by affecting soil microbial structure.

Tobacco bacterial wilt can be biologically controlled by the application of antagonistic strains in combination with organic fertilizer

Identification of benzoic acid and 3-phenylpropanoic acid in tobacco root exudates and their role in the growth of rhizosphere microorganisms

The invention discloses a distilled grain organic fertilizer and a production method of the distilled grain organic fertilizer. A fermentation material of the distilled grain organic fertilizer comprises the following components in parts by mass: 100 parts of distilled grains, 3-5 parts of straw, 1-2 parts of wood sawdust, 2-2.5 parts of quick lime and 0.2-0.3 part of a strain. The production method comprises the following steps: inoculating the fermentation material with the strain, uniformly mixing to construct a strip pile, and performing fermentation; heating the strip pile to 60-65 DEG C, and turning the pile; regulating the pile turning frequency under a principle of maintaining the temperature of the strip pile to be not more than 65 DEG C; naturally ventilating for 1-2 months after fermenting; further crushing and screening to obtain a distilled grain organic fertilizer final product. The method for producing the distilled grain organic fertilizer, disclosed by the invention, is short in fermentation time and controllable in fermentation degree; the obtained product comprises the following components in percentage by weigh: 76% of an organic matter, 4% of N, 2.18% of P2O5, 1.29% of K2O, 7.74% of total nutrients and 29% of moisture; the pH value of the product is 6.2; indicators of the mortality of roundworm eggs and the number of fecal coliforms of the product can meet the requirements of NY884.

Distilled grain organic fertilizer and production method thereof

Tobacco bacterial wilt caused by Ralstonia solanacearum is a serious disease affecting tobacco cultivation in southwest China. The response surface methodology was employed to evaluate the optimal conditions of tobacco bacterial wilt, and green fluorescent protein gene (gfp) labelling was applied to monitor the location and survival dynamics of R. solanacearum (Rs::gfp) on tobacco roots and in soil under these optimal conditions. The results showed that the highest wilt incidence was 91.13%, which occurred when the population reached 6.6 × 106 CFU/g soil, the temperature was 30.55 °C, and the humidity was >81.42%. The Rs::gfp densely colonized the root tips and root hairs, and cells of Rs::gfp were observed intermittently in the elongation zone or at the point of the emerging lateral roots. The Rs::gfp number in the rhizosphere soil was 10.75-, 73.13- and 74.86-times higher than that in the bulk soil at 10, 15 and 20 days after transplantation, respectively. Increased colonization by Rs::gfp was related to the population of the pathogen, the environmental temperature and the humidity in the soil. These three conditions determined whether R. solanacearum would induce tobacco wilt. This is the first study to investigate factors affecting the virulence of a tobacco wilt bacterial pathogen, which is important for conducting field diagnosis and biocontrol of tobacco bacterial wilt.

Factors affecting the virulence of Ralstonia solanacearum and its colonization on tobacco roots

The invention discloses a screening method of a pseudomonas solanacearum bacteriophage resource. The screening method comprises the following steps: S1, taking a soil sample, treating the sample, and filtering by a filter membrane to obtain a filtrate; S2, culturing a pseudomonas solanacearum strain to obtain a pseudomonas solanacearum liquid; S3, co-culturing the filtrate in the S1 and the pseudomonas solanacearum in the S2; and S4, selecting and storing bacteriophage plaque, wherein the used material comprises sterile water, the pseudomonas solanacearum strain, a CPG culture medium, agar powder and low-melting-point agar. The CPG culture medium comprises a CPG solid culture medium and a CPG liquid culture medium. The method can be applied to screening the pseudomonas solanacearum bacteriophage resource from tobacco-planting soil, bacterial wilt soil and sewage and providing and collecting the pseudomonas solanacearum bacteriophage resource for researching prevention and control of tobacco bacterial wilt by using the pseudomonas solanacearum bacteriophage.

Shi Junxiong

Papers

Tobacco bacterial wilt can be biologically controlled by the application of antagonistic strains in combination with organic fertilizer

Identification of benzoic acid and 3-phenylpropanoic acid in tobacco root exudates and their role in the growth of rhizosphere microorganisms

Distilled grain organic fertilizer and production method thereof

Factors affecting the virulence of Ralstonia solanacearum and its colonization on tobacco roots

Screening method of pseudomonas solanacearum bacteriophage resource