Abstract: In the present work，a specific primer pair Pst3F/Pst3R was designed based on the pathogenicity-related gene HrpZ of Pseudomonas syringae pv. tomato（Pst），and a target fragment of 161 bp was specifically amplified from the genomic DNA of Pst. A real-time fluorescent quantitative PCR（qPCR）assay was developed for quantifying Pst in contaminated tomato seeds and infected tissues. The detection sensitivity of qPCR established in this study was 1 000 times higher than that of conventional PCR. The detection threshold was 4.21 cfu per gram of artificially contaminated tomato seeds. The amount of Pst was detected to be 4.15 × 102 cfu per gram of inoculated leaves with disease-grade level 1. For naturally infected tomato tissue samples，PCR，qPCR and classical culture methods were used for determination of Pst. Quantifiable levels of Pst were detected in 54 out of the 63 samples，and the results of the three methods were consistent. These studies showed that qPCR assay is a highly rapid and reliable method to quantify Pst in tomato seeds and infected tissues of leaves，stems and fruits. Application of the assay may potentially improve pathogen identification and disease management.

Key words: tomato, Pseudomonas syringae pv. tomato, quantitative PCR, seed detection, tissue detection