Speakers - 2026

Title: Transcriptomic, proteomic, and marker profiling associated with resistance to cucumber phytophthora blight disease

Abstract

Cucumber Phytophthora blight, caused by Phytophthora melonis, is one of the most destructive diseases affecting cucumber production and is responsible for substantial economic losses worldwide. In the present study, a diverse set of 38 commercial cucumber genotypes was screened for resistance to P. melonis. Based on disease severity, the genotypes were classified as resistant, moderately resistant, moderately susceptible, or highly susceptible, with disease incidence ranging from 7.92% in resistant genotypes to 88.01% in highly susceptible genotypes. The genotypes were further characterized using 15 ISSR markers. A total of 317 bands were generated, of which 297 (93.69%) were polymorphic. The polymorphic information content (PIC) ranged from 0.34 to 0.45, the marker index (MI) from 5.78 to 9.45, and the resolving power (RP) from 9.68 to 14.95. Primer ISSR29 exhibited the highest RP, PIC, and MI values, indicating its suitability for genetic diversity analysis in cucumber. Cluster analysis and principal component analysis (PCA) revealed a potential association between genetic grouping and resistance level to P. melonis. These findings demonstrate the usefulness of ISSR markers for studying disease resistance and facilitating the development of resistant cucumber cultivars. To further elucidate the molecular mechanisms underlying resistance to P. melonis, crown and leaf samples were collected from four cucumber genotypes: Ramezz (resistant), Baby (moderately resistant), Mini 6-23, and Extrem (highly susceptible). Quantitative gene expression analyses were conducted for five defense-related marker genes, namely CsWRKY20, CsLecRK6.1, PR3, LOX1, and PR1-1a, at 24, 48, and 72 h after inoculation. Transcript levels of all five genes were significantly higher in the resistant and moderately resistant genotypes than in the susceptible ones. CsWRKY20 and PR3 showed peak expression in Ramezz at 48 h post-inoculation, whereas CsLecRK6.1 and LOX1 reached maximum expression at 72 h. In addition, PR1-1a exhibited its highest expression level in Baby at 72 h. The elevated expression of these defense-related genes suggests activation of plant defense pathways, thereby limiting the colonization capacity of P. melonis in Ramezz and Baby cultivars. These findings provide valuable insights into the molecular basis of the Cucumis sativus–P. melonis interaction and offer a useful resource for future functional genomics studies. In addition, changes in the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and polyphenol oxidase (PPO) were evaluated in the roots of two resistant genotypes (Soheil and Ramz), one moderately resistant genotype (Baby), and three highly susceptible genotypes (Extrem, Mini 6-23, and Yalda) at 7, 14, and 21 days after inoculation. The results revealed significant differences in defense-related enzyme activities between resistant and highly susceptible genotypes. Enzyme activities increased markedly in resistant and moderately resistant genotypes following inoculation, whereas no significant changes were observed in the non-inoculated controls. Overall, resistance to P. melonis was positively associated with POX and PAL activities but showed no significant correlation with PPO, SOD, or CAT activities. Therefore, further investigation of the physiological and metabolic pathways involving POX and PAL may provide important insights into the mechanisms of resistance to P. melonis in cucumber.

Based on presentation, the audience should take away the following key points:

1. Identification of resistant cucumber genotypes that can serve as valuable genetic resources for breeding programs aimed at developing cultivars resistant to Phytophthora melonis.
2. The effectiveness of ISSR markers for genetic diversity and resistance studies, with ISSR29 identified as a particularly informative marker for distinguishing cucumber genotypes and assessing resistance-related diversity.
3. The molecular basis of resistance to cucumber Phytophthora blight, including the important roles of defense-related genes (CsWRKY20, CsLecRK6.1, PR3, LOX1, and PR1-1a) in activating plant immune responses against P. melonis.
4. The significance of defense-related enzymes in disease resistance, particularly phenylalanine ammonia-lyase (PAL) and peroxidase (POX), whose activities were strongly associated with resistance, unlike CAT, SOD, and PPO.
5. The integration of molecular markers, gene expression profiling, and biochemical analyses as a comprehensive approach for understanding plant-pathogen interactions and accelerating the development of disease-resistant cucumber cultivars.
6. These takeaways highlight both the practical breeding applications and the biological mechanisms underlying resistance to cucumber Phytophthora blight.