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Citrus is a dominant fruit industry in China, which is of great significance for promoting rural revitalization. However, there are many natural pores on the surface of citrus fruits. During post-harvest storage and transportation, they are highly susceptible to infection by pathogens, leading to diseases. Among them, citrus green mold is caused by the infection of Penicillium digitatum. The disease progresses rapidly and is highly contagious, severely deteriorating the quality of fruits after harvest and causing huge economic losses to the citrus industry. Our research team targeted the pathogen of citrus green mold. An actinomycete strain, R2A-77, which exhibits excellent antagonistic effects against the pathogen of citrus green mold, was isolated and screened from the rhizosphere soil of red-orange plants in the Jiuzhoujiang Red-orange Orchard in Lianjiang, Zhanjiangy, Guangdong. The strain was characterized through morphological observation, physiological and biochemical tests, and molecular biological identification. The antibacterial activity of the fermentation broth was determined by measuring the diameter of the growth inhibition zone of the target bacteria according to the growth rate method. Single-factor and cross-combination experiments were conducted to optimize the fermentation conditions of the strain, aiming to enhance the antibacterial activity of the fermentation broth. The results indicated that the actinomycete R2A-77 was preliminarily identified as the genus Streptomyces. The optimal fermentation medium was sucrose 10 g/L, soybean peptone 35 g/L, and distilled water 1000 mL. The optimal fermentation conditions were as follows: initial pH of 7.0, fermentation time of 6 days, inoculum size of 3%, and liquid volume of 150 mL in a 250 mL flask. After optimization, the antibacterial activity of the fermentation broth of actinomycete R2A-77 increased by 15% compared to that before optimization, with an antibacterial rate of 98%. The results suggest that actinomycete R2A-77 has a good antagonistic effect against P. digitatum, demonstrating promising practical application prospects. It would accumulate resources for the green prevention and control of citrus green mold and lays a foundation for large-scale fermentation and the development of microbial agents in the future.
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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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