Phytophtora capsici causes major diseases in cucurbit crops worldwide. In this study, we inoculated this pathogen into Cucurbita pepo subsp. pepo susceptible MUCU-16 and C. moschata tolerant M63. The gene expression of plant pathogenesis-related proteins chitinase (CpChiIV), lignin-forming peroxidase (CpLPOX), and defensin (CpDEF) and hormone-related enzymes salicylic acid (CpPAL) and ethylene (CpACO) was analyzed for two weeks post-inoculation in root and crown tissues. Differentially expressed genes were found between genotypes, tissues, days post-inoculation, and inoculated/non-inoculated samples. After inoculation, CpPAL and CpChiIV (crown) were downregulated in MUCU-16, while CpLPOX and CpDEF were upregulated in M63. In inoculated samples, higher expression changes were presented on days 10-14 than on day 3 for CpACO, CpLPOX, and CpDEF genes. Overexpression was higher for CpDEF compared to the other tested genes, indicating good suitability as a marker of biotic stress. The overexpression of CpDEF was higher in crown than in roots for both inoculated genotypes. The basal expression of CpPAL and CpDEF was higher in MUCU-16, but after inoculation, CpPAL and CpDEF gene expression were higher in M63. These changes suggest an association between CpDEF upregulation and tolerance, and between CpPAL downregulation and susceptibility.
Keywords: Cucurbita moschata; Cucurbita pepo; defensin; squash; susceptibility; tolerance.