| 論文英文摘要 |
Lemon is an internationally important economic crop. In Taiwan, Kaohsiung and Pingtung are the main producing areas. During the growth period of crops, bacterial canker caused by Xanthomonas citri subsp. citri (Xcc) is often reduce its quality. Due to the demand on disease control, this study mainly explores whether the fermentation broth established by using Bacillus amyloliquefaciens PMB05, which can enhance plant immune signals and further contribute to control bacterial canker. Firstly, it was confirmed that the bacterial suspension of B. amyloliquefaciens PMB05 enhanced the plant immune signals such as reactive oxygen generation and callose deposition induced by Xcc on lemon leaves. B. amyloliquefaciens PMB05 also exhibited good survival ability on lemon leaves. Furthermore, in the greenhouse test of PMB05, the disease severity of bacterial canker can be significant reduced by 25.6% in the treatment with the bacterial suspension. To further develop its fermentation broth, bacteria amount and sporulation rate were used as indicators to evaluate the formula in 500 mL flasks and 30 L fermentation tanks. In the 500 mL shake flask culture, results revealed that the carbon to nitrogen ratio of 3:1 can achieve the highest cell yield and sporulation rate, and this fermentation broth is called PMBFL-2A. Furthermore, the 30 L fermentation tank also showed that PMBFL-2A had the highest sporulation rate under the 120 rpm and 1.5 vvm. The shelf life assay showed that the 54 °C treatment for two weeks and the treatment at 4, 25, and 37 °C for 8 months can maintain more than 90% of the bacterial population in PMBFL-2A. At the same time, we also proved that the PMBFL-2A fermentation broth can significantly enhance the immune response of PMB05 on lemon leaves compared to that of the bacterial suspension. After 100, 200 and 500 folds dilutions of PMBFL-2A, the occurrence of bacterial canker was reduced by 64.4, 61.0, and 53.0% in disease severity, respectively, in the greenhouse. In 2020, the field trial conducted in Ligang, Pingtung County, the control rate reached 100% to the third month. In summary, this study has established the optimal fermentation conditions for Bacillus amyloliquefaciens PMB05, which can enhance plant immune response, and has the potential to be used in the field to control bacterial canker of lemon. |