Abstract: Tea plant is an important economic crop in China. Long-term continuous cropping of tea plants has resulted in severe problems such as the imbalance of soil microbial community structure, soil disease exacerbation. Exploring the molecular mechanism underlying the formation of continuous cropping obstacles in Tieguanyin tea gardens is of great significance for seeking effective techniques for preventing and controlling the continuous cropping obstacle phenomenon. In this study, the pathogen and its antagonistic bacteria were isolated from the rhizosphere of Tieguanyin tea garden and identified by methods such as microbial isolation and purification, and plate confrontation. Quantitative analysis was conducted on the number of pathogen and its antagonistic bacteria in the rhizospheric soils of different continuous cropping years (0, 1, 10, and 20 years). Simultaneously, high-performance liquid chromatography (HPLC) technology was used to detect the changes of phenolic acid contents in the rhizospheric soils of different continuous cropping years, and the ratio of various phenolic acids in the soils was simulated to investigate the effects of phenolic acids on the rhizospheric pathogen and its antagonistic bacteria. The results show that one pathogenic fungus Alternaria sp. was isolated and identified from the infected roots of Tieguanyin under 20 years’ continuous cropping, and an antagonistic bacteria Pseudomonas sp. was identified from the rhizospheric soils. Fluorescence quantitative PCR analysis shows that the content of Alternaria sp. in 20 years’ continuous cropping soils was significantly higher than 1 year tea garden, while the content of Pseudomonas sp. was significantly lower. Five phenolic acids, including p-hydroxybenzoic acid, vanillic acid, syringic acid, vanillin, and ferulic acid, were detected in the rhizospheric soils, with an average ratio of 38∶229∶11∶11∶3. Phenolic acids did not accumulate in the soils, but showed a trend of first increasing and then decreasing with the increase of continuous cropping years. Simulation experiments found that mixed phenolic acids at low to medium concentrations (30-120 mmol·L^-1) could significantly promote the mycelial growth of Alternaria sp. while single phenolic acid such as p-hydroxybenzoic acid, vanillic acid, and syringic acid at low concentrations (30 mmol·L^-1 and 60 mmol·L^-1) also significantly accelerated the mycelial growth of Alternaria sp.. However, p-hydroxybenzoic acid had an inhibitory effect on the growth of Pseudomonas sp., and the inhibitory effect increased with the increase of p-hydroxybenzoic acid concentration. Mixed phenolic acid and other single phenolic acids had no significant effect on the growth of Pseudomonas sp.. Therefore, phenolic acids, the root exudates of Tieguanyin tea plants, have different ecological effects on the key microbial communities in the rhizospheric soils, and are important factors causing the imbalance of microbial community structure and the increase of severe diseases and other continuous cropping obstacles. The research results provided a theoretical basis for further revealing the mechanism of continuous cropping obstacles in Tieguanyin tea plants.

Key words: tea plant, continuous cropping obstacles, phenolic compounds, Alternaria sp., Pseudomonas sp.