Abstract:

【Objective】Plum cultivation is an important industry in Liaoning region, while the large-scale epidemic of bacterial shot hole has seriously affected the sustainable development of plum cultivation. The purpose of this paper is to clarify the pathogenic bacteria species of plum bacterial shot hole in Liaoning, and to explore the toxicity of different agents against the pathogenic bacteria, so as to provide a theoretical basis for the prevention and control of the disease.【Method】From 2023 to 2024, the occurrence of plum bacterial shot hole was investigated in 10 plum production areas of Liaoning Province. By collecting 20 disease samples of leaves, fruits, and twigs with typical symptoms, a total of 30 pathogenic bacteria were isolated, purified and preserved. The characteristics of these colonies including morphology, color, size and edge morphology were observed and recorded. Transmission electron microscopy was employed to further observe their morphology and the Gram staining was performed. The bacterial 16S rDNA universal primer 27F/1492R and multiple gene loci were used for amplification. The sequencing result was compared by BLASTn analysis in the NCBI database and the reference sequences of the corresponding genera were downloaded. Then, a multi-gene joint phylogenetic tree was constructed using the maximum likelihood method on the website of GIPRES Science Gateway. Subsequently, the leaves of ‘Qiu Ji’ plum were inoculated with pathogenic bacteria by the stab inoculation of bacterial suspension, and then cultivated at 28 ℃ under high humidity. The disease occurrence of the leaves was regularly observed and recorded. Furthermore, the pathogenic bacteria were re-isolated from the disease-health junction of the leaves to complete the verification of the whole Koch’s postulates. The sensitivities of pathogenic bacteria to 0.15% tetramycin, 80% ethylicin, 3% benziothiazolinone, 1.8% octylamine, 3% zhongshengmycin and 6% kasugamycin were determined by the inhibition zone method, respectively.【Result】Based on morphological observation and molecular biology identification, the pathogenic bacteria were identified as Xanthomonas arboricola pv. pruni (Xap) (36.67%, 11 strains) and Pantoea vagans (63.33%, 19 strains). The sensitivity results demonstrated that the best inhibitory activities were achieved by 0.15% tetramycin and 80% ethylicin, with the EC₅₀ of 0.15% tetramycin being 0.026 and 0.502 μg·mL^-1 for Xap and P. vagans, respectively, and that of 80% ethylicin being 1.162 and 25.643 μg·mL^-1, respectively. The second was 3% benziothiazolinone, and its EC₅₀ values against Xap and P. vagans were correspondingly 5.200 and 96.075 μg·mL^-1, followed by EC₅₀ of 1.8% octylamine against Xap and P. vagans of 176.008, 273.072 μg·mL^-1, and 3% zhongshengmycin against Xap and P. vagans of 621.697 and 72.270 μg·mL^-1. As for 6% kasugamycin, it had an EC₅₀ of 886.467 μg·mL^-1 for P. vagans and was less effective in inhibiting Xap.【Conclusion】The pathogens causing plum bacterial shot hole in Liaoning were identified as Xap and P. vagans. Moreover, the 0.15% tetramycin and 80% ethylicin were screened and selected as exerting better inhibitory effects on these two pathogens. The results of the study will provide a theoretical basis for the precise prevention and control of plum bacterial shot hole in the field.

Key words: plum, bacterial shot hole, pathogen identification, toxicity, Xanthomonas arboricola pv. pruni (Xap), Pantoea vagans