Researchers from Egypt have demonstrated that specific strains of Bacillus bacteria and the fungus Trichoderma asperellum can effectively control bacterial wilt in tomato plants. The study, published in the Egyptian Journal of Biological Pest Control, evaluated these biological control agents through both in vitro laboratory tests and in vivo greenhouse experiments. The findings indicate that these microbial antagonists not only suppress the pathogen Ralstonia solanacearum but also enhance plant growth and improve fruit quality. This approach offers a potential alternative to chemical pesticides, which are often limited by environmental concerns and inconsistent efficacy.
Bacterial wilt is a severe disease affecting solanaceous crops, including tomatoes, peppers, and potatoes, as well as other vital crops like peanuts and bananas. The pathogen, Ralstonia solanacearum, has a broad host range and can inhabit approximately 450 crop species. Management of this disease is challenging due to the pathogen’s vascular residence, extended soil viability, and high variability. Traditional control methods, such as crop rotation and the use of resistant cultivars, often face limitations including protracted breeding cycles and the pathogen’s ability to overcome resistance. Consequently, biological control has emerged as a preferred strategy for managing bacterial wilt in an environmentally responsible manner.
The study focused on four specific microbial antagonists: Bacillus subtilis, Bacillus pumilus, Bacillus chitinosporus, and Trichoderma asperellum. These strains were selected from a mass screening test for their capacity to inhibit R. solanacearum. The research team isolated the causal pathogen from wilted potato tubers and soil samples in various Egyptian governorates, including Beheira, Kafr El-Sheikh, and El-Menoufia. Five isolates of R. solanacearum were identified, with R1 and R2 showing the highest pathogenicity in subsequent tests on tomato seedlings. These two strains were used for the primary evaluation of the biocontrol agents.
In the in vitro experiments, the antagonistic effects of the biocontrol strains were assessed on King’s B agar plates. The results showed that B. pumilus provided the best inhibition zone against both R1 and R2 strains of R. solanacearum. B. subtilis also significantly inhibited the development of the pathogen. The linear growth of R. solanacearum was reduced in the presence of these bioagents, indicating their potential to suppress pathogen growth in a controlled environment. These laboratory findings supported the selection of these strains for further in vivo evaluation under greenhouse conditions.
The in vivo experiments were conducted in pots under greenhouse conditions over two growing seasons, 2022 and 2023. Tomato hybrid N23 seedlings were planted in clay soil and treated with the biocontrol agents. The bacterial strains were propagated in liquid nutrient broth, while T. asperellum was propagated in potato dextrose broth. The plants were inoculated with R. solanacearum, and the disease severity, efficacy, and area under the disease progress curve (AUDPC) were measured. The results demonstrated that all four biocontrol agents reduced disease severity compared to the untreated control. B. pumilus achieved the highest efficacy, with percentages ranging from 55.2% to 62.8% in the first season and 58.6% to 61.7% in the second season.
Trichoderma asperellum showed particularly strong effects on plant growth and yield parameters. In the 2022 season, plants treated with T. asperellum had higher total chlorophyll levels, measured at 89.0 and 76.5 SPAD units for R1 and R2 infections, respectively. The treatment also increased plant height to 45.0 cm in 2022 and 53.3 cm in 2023. Additionally, all microbial antagonists increased fresh and dry weights, number of leaves, number of flowers, and yield per plant. These growth-promoting effects suggest that the bioagents not only control the disease but also enhance the overall vigor of the tomato plants, potentially through mechanisms such as nutrient solubilization and the synthesis of indole-3-acetic acid (IAA).
Fruit quality was also improved by the biocontrol treatments. T. asperellum resulted in increased fruit weight, reaching 96.2 g and 94.6 g in the first season and 115.6 g and 109.0 g in the second season for R1 and R2 infections, respectively. The treatment also led to significant improvements in fruit diameter, pH, hardness, total soluble solids (TSS), and vitamin C content. For instance, in the first season, T. asperellum produced fruits with a diameter of 55.6 mm and a TSS percentage of 5.0%. These quality parameters are crucial for marketability and consumer preference, indicating that biological control can have positive impacts on the commercial value of the crop.
The study also investigated the molecular mechanisms underlying the plant’s response to the biocontrol agents. Using real-time quantitative polymerase chain reaction (RT-qPCR), the researchers measured the expression of pathogenesis-related (PR) genes PR-2 and PR-3 in tomato leaves. PR-2 encodes a beta-1,3-glucanase, and PR-3 encodes a chitinase, both of which are involved in plant defense against pathogens. The results showed that T. asperellum induced the highest up-regulation of these genes, with relative expression levels of 4.7-fold for PR-2 and 5.4-fold for PR-3. B. pumilus also significantly increased the expression of PR-2 and PR-3. This elevated activation of defense genes suggests that the bioagents trigger systemic resistance in the plants, enhancing their ability to combat the pathogen.
The use of biological control agents offers several advantages over chemical pesticides. Biocontrol agents can be self-sustaining, spread on their own after initial establishment, and require less non-renewable resource input. They can also suppress disease over the long term in an environmentally friendly way. The mechanisms by which these agents work include competition for nutrients and space, parasitism, antibiosis, and induced systemic resistance. The production of secondary metabolites, such as polyketides and antibiotics, by Bacillus species further contributes to their biocontrol capability. These metabolites can inhibit the activities of pathogenic bacteria while stimulating plant growth.
Despite the promising results, the study has certain limitations. The experiments were conducted under controlled greenhouse conditions, which may not fully replicate the complexities of field environments. The long-term efficacy of these biocontrol agents in various ecological zones remains to be explored. Additionally, the commercial use possibilities of these strains need further investigation. Future studies should focus on testing the safety and stability of these bioagents in diverse agricultural settings. The findings of this study support the use of Bacillus subtilis, B. pumilus, B. chitinosporus, and T. asperellum as promising strategies for sustainable agriculture, enhancing crop protection and productivity while minimizing the environmental impact of chemical pesticides.
The pathogen Ralstonia solanacearum is described as the second most significant bacterial pathogen causing vascular wilt disease. The study notes that direct yield losses are strongly correlated with host, environment, cultivar, soil type, cropping pattern, and pathogen strain. For potatoes, output losses ranged from 33 to 90%, while for tomatoes, losses ranged from 0 to 91%. The pathogen’s genetic diversity and genotype-by-environment interactions frequently overcome crop resistance, making traditional control methods less reliable. The broad host range of bacterial wilt also makes crop rotation-based control difficult, as the pathogen can inhabit approximately 450 crop species. This context underscores the need for biological control agents that can provide consistent protection without relying solely on resistant cultivars or chemical interventions.
In the in vitro phase, the antagonistic effects were assessed on King’s B agar plates using R. solanacearum isolates R1 and R2. The results indicated that B. pumilus provided the best inhibition zone compared to other treatments and the untreated control. B. subtilis and B. pumilus significantly inhibited the development of R. solanacearum. The linear growth of the pathogen was reduced in the presence of these bioagents, demonstrating their potential to suppress pathogen growth in a controlled environment. These laboratory findings supported the selection of these strains for further in vivo evaluation. The in vitro tests confirmed that the selected microbial antagonists possess the capacity to inhibit the growth of the causal pathogen before being applied to living plants.
The in vivo experiments were conducted under greenhouse conditions over two growing seasons, 2022 and 2023. Tomato hybrid N23 seedlings were planted in clay soil and treated with the biocontrol agents. The bacterial strains were propagated in liquid nutrient broth, while T. asperellum was propagated in potato dextrose broth. The plants were inoculated with R. solanacearum, and disease severity, efficacy, and area under the disease progress curve (AUDPC) were measured. The results demonstrated that all four biocontrol agents reduced disease severity compared to the untreated control. B. pumilus achieved the highest efficacy, with percentages ranging from 55.2% to 62.8% in the first season and 58.6% to 61.7% in the second season. The fungicide copper hydroxide also demonstrated efficacy, with percentages of 66.7% and 65.4% in the first season, and 71.0% and 67.3% in the second season for R1 and R2, respectively.
Trichoderma asperellum showed particularly strong effects on plant growth and yield parameters. In the 2022 season, plants treated with T. asperellum had higher total chlorophyll levels, measured at 89.0 and 76.5 SPAD units for R1 and R2 infections, respectively. The treatment also increased plant height to 45.0 cm in 2022 and 53.3 cm in 2023. Additionally, all microbial antagonists increased fresh and dry weights, number of leaves, number of flowers, and yield per plant. These growth-promoting effects suggest that the bioagents not only control the disease but also enhance the overall vigor of the tomato plants. The enhancement in plant growth and nutrient absorption is likely caused by the strains’ capacity to solubilize phosphate and potassium, as well as their synthesis of indole-3-acetic acid (IAA). The Bacillus genus is renowned for its phosphate and potassium solubilizing capabilities, which contribute to the observed growth improvements.
Fruit quality was also improved by the biocontrol treatments. T. asperellum resulted in increased fruit weight, reaching 96.2 g and 94.6 g in the first season and 115.6 g and 109.0 g in the second season for R1 and R2 infections, respectively. The treatment also led to significant improvements in fruit diameter, pH, hardness, total soluble solids (TSS), and vitamin C content. For instance, in the first season, T. asperellum produced fruits with a diameter of 55.6 mm and a TSS percentage of 5.0%. These quality parameters are crucial for marketability and consumer preference, indicating that biological control can have positive impacts on the commercial value of the crop. The study highlights that biological control agents can improve both the health and the economic value of the produce.
The study also investigated the molecular mechanisms underlying the plant’s response to the biocontrol agents. Using real-time quantitative polymerase chain reaction (RT-qPCR), the researchers measured the expression of pathogenesis-related (PR) genes PR-2 and PR-3 in tomato leaves. PR-2 encodes a beta-1,3-glucanase, and PR-3 encodes a chitinase, both of which are involved in plant defense against pathogens. The results showed that T. asperellum induced the highest up-regulation of these genes, with relative expression levels of 4.7-fold for PR-2 and 5.4-fold for PR-3. B. pumilus also significantly increased the expression of PR-2 and PR-3. This elevated activation of defense genes suggests that the bioagents trigger systemic resistance in the plants, enhancing their ability to combat the pathogen. The findings provide a molecular basis for the observed disease control and growth promotion effects.
The use of biological control agents offers several advantages over chemical pesticides. Biocontrol agents can be self-sustaining, spread on their own after initial establishment, and require less non-renewable resource input. They can also suppress disease over the long term in an environmentally friendly way. The mechanisms by which these agents work include competition for nutrients and space, parasitism, antibiosis, and induced systemic resistance. The production of secondary metabolites, such as polyketides and antibiotics, by Bacillus species further contributes to their biocontrol capability. These metabolites can inhibit the activities of pathogenic bacteria while stimulating plant growth. The study concludes that these bioagents could reduce the cost of disease management and minimize the environmental impact of chemical pesticides, supporting their use in sustainable agriculture.
Subject of Research: Biological control of tomato bacterial wilt using Bacillus and Trichoderma
Article Title: Efficacy of Bacillus spp. and Trichoderma asperellum for biological control of bacterial wilt disease in tomato: in vitro and in vivo evaluations
Article References: Elsharkawy, M. M., Kamel, S. M., Fathallah, G., & Khedr, A. A. (2025). Efficacy of Bacillus spp. and Trichoderma asperellum for biological control of bacterial wilt disease in tomato: in vitro and in vivo evaluations. Egyptian Journal of Biological Pest Control, 35(1), Article 39. https://doi.org/10.1186/s41938-025-00877-w
Image Credits: AI Generated
DOI: 10.1186/s41938-025-00877-w
Keywords: Bacterial Wilt, Tomato, Bacillus, Trichoderma, Biological Control, Ralstonia solanacearum, Plant Pathology, Sustainable Agriculture, Greenhouse Study, Gene Expression, Efficacy, asperellum
News Source: Alan Morgan. (November 11, 2026). Bacillus and Trichoderma Strains Control Tomato Bacterial Wilt. Scienmag.
