2018 ASHS Annual Conference

Downy mildew caused by the oomycete Pseudoperonospora cubensis generates significant yearly losses of cucumbers and related crops in Poland and worldwide. In our study, we chose five cucumber cultigens showing a broad range of P. cubensis reactions, and submitted them to laboratory bio-assays with an aggressive local pathogen isolate, to observe the important subcellular, biochemical, and transcriptomic reactions. DCFDA staining evidenced participation of the reactive oxygen species (ROS) in response to P. cubensis infections. An increasing proportion of ROS was found over time, with only a slight increase in their content in the resistant cultigens compared to the susceptible ones. Differences in the activitiy of SOD, PPO, and POX, corresponded with the P. cubensis resistance level of the tested cultigens. The resistant cultigens showed a significant increase in enzymatic activity at 8 hours after inoculation (hpi), whereas the susceptible ones displayed such increase only after 36 hpi. In case of the protective substances, there was an upward trend in the content of free phenols and lignins, with a clearer tendency in the resistant cultigens. Transcriptomic analyses included qPCR investigations of 19 cucumber transcripts (salicylic acid related: 2; jasmonic acid related: 4; PR genes: 8; PAL; LOX; CalSyn; VPE) normalized to housekeeping genes. All these analyses pointed to a comparatively earlier activation of the defenses in the P. cubensis-resistant cultgens.