Abstract:

【Objective】 The endophytic bacterial diversity in the Huanglongbing pathogen-infected and healthy citrus phloem tissue in Guangxi were investigated in order to decipher the interactions of Huanglongbing pathogen with companion microbe. 【Method】Both classical morphological, physiological, chemotaxonomic characteristics methodology and 16S rRNA, and PCR-RFLP analysis methods were applied. 【Result】 By the traditional isolation and identification and 16S rDNA amplificons methods, 10 genera of bacteria were identified from 21 culturable bacterial populations. The sequences aligned with NCBI GenBank database and showed that they belonged to 10 different genera of bacterium. The dominant bacterial population in healthy citrus belonged to Bacillus sp., Pseudomonas sp., and Kocuria sp.. While in phloem tissue of infected citrus plant over ten years were Bacillus sp., Pseudomonas sp., Kocuria halotolerans, and Microbacterium sp.. By the PCR-RFLP methods, two 16S rDNA clone libraries of endophytic bacteria were constructed and 29 restriction endonuclease types were detected, 10 genera of bacteria and 11 genera of uncultured bacteria were identified. The dominant bacterium population in libraries belonged to Dyella sp., Pseudomonas sp., Serratia sp. and uncultured bacterium. The density and species of endophytic bacteria were observed in remarkable difference compared disease tree to healthy one. 【Conclusion】 By traditional cultivation and 16S rDNA sequencing, PCR-RFLP analysis, the diversity of population and species of endophytic bacteria mainly in citrus phloem tissue has difference among infected and healthy citrus plant, while those dominant bacterial populations if related to Huanglongbing pathogen is currently still under investigation.

Key words: Huanglongbing, endophytic bacteria, 16S rDNA, RFLP, bio-diversity