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.

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.

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.

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.

The plum is one of the most widely distributed and cultivated fruit trees globally. The Chinese plum (Prunus salicina L.), originating from China, is known for its beauty, fragrance, juiciness, and rich nutritional value. It exhibits significant genetic heterogeneity and diversity in fruit traits. In recent years, there has been an increasing demand for the sensory quality of plum fruit aroma, prompting breeders to place greater emphasis on identifying and selecting germplasm with unique aromas. Those onventional methods for detecting fruit aroma involve complex preprocessing, high testing costs, and require high technical skills for operation. Additionally, these methods lack the advantages of rapid response and high detection speed, making non-destructive testing difficult and unable to accurately simulate consumer olfactory experiences.

The aim of this study aimed to use electronic nose technology to evaluate the diversity of aroma composition in Chinese plum germplasm, so as to provid essential materials and data support for plum breeding research and production practices in China.

Using electronic nose technology, ten odor sensors were employed to identify the different fruit fragrances of 94 Chinese plum germplasm resources. The samples were then grouped and evaluated based on the results of K-means clustering.

Overall, the average values of different odors showed a normal distribution, but significant differences existed between different odor channels. The W1W channel exhibited the highest odor response value, while the W1C channel had the lowest value. Additionally, variance analysis of different odor channels revealed that W1W had the highest degree of dispersion in odor response values, followed by W5S, while W1C, W3C, W5C, and W3S showed lower dispersion and relatively concentrated distribution. The aroma data of 94 Chinese plum samples were divided into six groups using K-means clustering analysis, each representing plum fruits with specific aroma characteristics. Group one included germplasm sensitive to aromatic hydrocarbons, Group two to ethanol and nitrogen oxides, Group three to hydrogen, Group four to hydrogen and aromatic hydrocarbons, Group five showed low sensitivity to aromatic hydrocarbons, and Group six to hydrogen sulfide. These groupings provided important insights for further research on the aroma components and sensory quality of Chinese plum fruits. Significant differences in maximum, minimum, and median values of different odors were observed between groups. Further correlation analysis revealed significant positive or negative relationships between some odors. Principal component analysis (PCA), linear discriminant analysis (LDA), and uniform manifold approximation and projection (UMAP) were used for dimensionality reduction and visualization of aroma data, and the results indicated that these methods could distinguish the tested plum germplasm to varying degrees and correspond to their cluster groupings, each with different advantages and disadvantages in feature extraction and data visualization. Particularly, the independent use of LDA analysis had certain limitations and shortcomings. This study screened a batch of plum resources with prominent aroma characteristics, including ‘Wuxiangli’ ‘Zaoshuli’ ‘Lishuihong’ ‘Longnanli’ and ‘Xiangjiaoli (Fuxian)’.

This study utilized electronic nose technology to analyze the aroma composition and distribution of Chinese plum germplasm, revealing that the W1W, W1S, and W5S channels had higher response values, primarily sensitive to volatile compounds such as hydrogen sulfide, methane, and nitrogen oxides. Six Chinese plum groups had different distinct aroma characteristics. In several response values, the mean difference between cluster 6 and the other five groups was significant, indicating that cluster 6 had unique characteristics in these response values.