Detectability of Pseudomonas syringae pv. aesculi from European Horse Chestnut Using Quantitative PCR Compared with Traditional Isolation

Bleeding cankers on horse chestnut trees (Aesculus hippocastanum and Aesculus x carnea), caused by Pseudomonas syringae pv. aesculi, have been reported across Europe. In the present study, we show the successful detection of P. syringae pv. aesculi on symptomatic horse chestnut trees in Switzerland using quantitative PCR (qPCR). However, P. syringae pv. aesculi was also detected by qPCR on trees from which no isolate was obtained through cultivation. Reduced isolation success and low copy numbers of the target gene were correlated with the increasing age of symptomatic horse chestnut trees. The potential of detecting non-viable P. syringae pv. aesculi by qPCR was evaluated using an inoculation experiment with dead bacteria and detection by qPCR and cultivation. The detectability of DNA from P. syringae pv. aesculi cells dropped by 34.5% one day after inoculation and then decreased only slightly until the end of the experiment (22 days after inoculation). In contrast, no bacterial growth was observed at any time point after the inactivation of the bacteria. To protect horse chestnut trees, evaluating the viability and actual infection stage of the bacterium may play an important role.

Automated summary

This study successfully detected Pseudomonas syringae pv. aesculi on symptomatic horse chestnut trees in Switzerland, and found that reduced isolation success and low copy numbers of the target gene were correlated with the increasing age of symptomatic trees. The experiment showed that detectability of DNA from the bacteria dropped by 34.5% one day after inoculation and remained relatively stable until the end of the experiment, while no bacterial growth was observed after inactivation.