Effects of phenolic acid accumulation in tomato rhizosphere on Ralstonia solanacearum invasion

【Objective】 This study aimed to investigate the effects of phenolic acid accumulation in the tomato rhizo-sphere on the invasion of Ralstonia solanacearum，providing theoretical support for elucidating the pathogenesis of tomato bacterial wilt. 【Method】 The effects of 5 phenolic acid substances（phenylpropanoic acid，benzoic acid，caffeic acid，ferulic acid and syringic acid）on the growth of R. solanacearum were examined using 96-well plate culture. The changes in soil bacterial community diversity after phenolic acid accumulation were detected using high-throughput sequencing methods. The population changes of R. solanacearum in soil were detected using selective culture media. Principal component analysis（PCA），redundancy analysis（RDA）and correlation analysis were employed to analyze the effects of soil bacterial community changes on the growth and reproduction of R. solanacearum under different phenolic acid treatments. 【Result】 Phenylpropanoic acid，benzoic acid，caffeic acid，ferulic acid and syringic acid promoted R. solanacearum growth，with caffeic acid showing the most obvious effect. The OD_{600 nm} of R. solanacearum reached 0.17 in the caffeic acid treatment，which was significantly higher than those in other treatments（P<0.05，the same below）. Compared with blank control，the continuous accumulation of each phenolic acid substance significantly reduced the diversity indexes of soil bacterial communities（Sobs，Shannon，ACE and Chao1 indexes）. After benzoic acid，caffeic acid，feru‐ lic acid and syringic acid treatments，the dominant phyla shifted from Proteobacteria to Firmicutes. The relative abundance of Firmicutes in soil was the highest in the syringic acid treatment，reaching 90.4%. However，the phenylpropanoic acid treatment showed a significant different trend compared with other phenolic acid treatments，with Proteobacteria becoming the dominant phylum（47.3% relative abundance）. RDA revealed a positive correlation between relative abundance of Firmicutes and soil organic matter content，and a positive correlation between relative abundance of Proteobacteria and pH，NO₃-N，NH₄-N. After 28 d of R. solanacearum inoculation in soils treated with phenolic acids，the reproductive quantity of R. solanacearum was significantly higher than that of blank control，with the highest population（8.16 lg CFU/g soil）observed in the syringic acid treatment. Correlation analysis showed that the population of R. solanacearum was significantly positively correlated with the relative abundance of Firmicutes，but it was significantly negatively correlated with the relative abundance of other communities. 【Conclusion】 The accumulation of phenolic acid substances in tomato rhizosphere disrupts the soil bacterial community structure，weakening its resistance to R. solanacearum invasion and accelerating disease development.