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Objective Southern blight, caused by Sclerotium rolfsii Sacc., is a major soil-borne disease that limits peanut production. At present, its management relies mainly on chemical fungicides. To improve the field control efficacy, reduce fungicide application rates, and lower pesticide residues in peanuts, this study screened antagonistic microorganisms against S. rolfsii and evaluated their synergistic effects with chemical fungicides in the control of peanut southern blight. The results are expected to provide technical support for the green and sustainable management of this disease. Methods This study first used a plate-based screening assay to obtain biocontrol strains showing strong antagonistic activity against S. rolfsii and high compatibility with commonly used fungicides. Next, a fungicide screening assay was conducted to identify control agents that effectively inhibited S. rolfsii without adversely affecting the growth of the biocontrol strains. Subsequently, an in vitro combined toxicity assay was performed. The pathogen was inoculated onto PDA plates containing different concentrations of thifluzamide (0.15 and 0.30 μg/mL), sterile 10% fermentation broth of H02, or their mixtures. Fungal growth was observed, and the inhibition rate and inhibition ratio (IR) were calculated to evaluate the interaction type of the combined treatment. Finally, a pot experiment was carried out to compare the control efficacy against peanut southern blight among the fermentation broth, the full-dose fungicide (recommended field rate), and the combination of fermentation broth with a half-dose fungicide. Results A Burkholderia gladioli strain H02 with high antagonistic activity and good fungicide compatibility was screened out, exhibiting an inhibition rate of 76.03%. Concurrently, thifluzamide was identified as a fungicide with strong inhibitory activity against S. rolfsii and no negative impact on the growth of strain H02, exhibiting an EC50 of 0.151 3 μg/mL. Results from the in vitro combined toxicity assay indicated that the combination of the H02 fermentation broth and thifluzamide showed an IR greater than 1, exhibiting a synergistic effect. Moreover, the combination of half the concentration of thifluzamide with the fermentation broth significantly demonstrated higher inhibition rates against pathogen mycelia and sclerotia (74.91% and 95.58%, respectively) than the full concentration of thifluzamide alone (68.04% and 83.67%, respectively). Pot experiment results showed that the combination of H02 fermentation broth and half dosage of thifluzamide had the control efficacy comparable to that of the full dosage of thifluzamide (68.94% vs. 66.63%), whereas the single application of H02 fermentation broth provided the control efficacy of 61.17%. Conclusion The combined application of B. gladioli H02 and thifluzamide can achieve synergistic control of peanut southern blight and reduce chemical fungicide usage while maintaining effective disease control, thus showing promising potential for practical application.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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