The effect of potassium phosphite on PR genes expression and the phenylpropanoid pathway in cucumber (Cucumis sativus) plants inoculated with Pseudoperonospora cubensis

- Potassium phosphite primes defense responses against Pseudoperonospora cubensis.
- KPhi acts via activation of PR genes and phenylpropanoid pathway.
- KPhi application is more effective before than after pathogen infection.

In the present study, the impact of potassium phosphite (KPhi) was investigated at molecular and biochemical levels in response to Pseudoperonospora cubensis infection in cucumber plants. Real-time PCR was employed to explore the differential expression of defense genes against P. cubensis. The highest expression for thaumatin-like protein (TLP), Ribosome-inactivating protein (RIP) and Defensin genes was observed in pre-inoculation plants at 96, 72 and 48 h, respectively. These findings revealed the involvement of these genes in the defense response of cucumber leaves after KPhi treatment and pathogen inoculation. At the biochemical level, more induction in the contents of some end-products of phenylpropanoid pathway, such as phytoalexin, phenolic component, flavonoid and anthocyanin as well as phenylalanine ammonia-lyase (PAL) enzymatic activity was detected in pre-inoculation plants compared to post-inoculation plants at all-time points. Data suggest that KPhi primes rapid and robust response in plants against infection via activation of defense responses. The negative effects of P. cubensis on cucumber plants could be considerably mitigated by KPhi application before infection.