Relationships between susceptibility levels of some pumpkin cultivars (Cucurbita pepo L.) to fusarium proliferatum and phenolic compounds

The sensitivities of four different pumpkin cultivars (cvs. Çağlayan, Mert Bey, Sena Hanım, and TG38) to Fusarium proliferatum, which causes crown and root rot in pumpkin (Cucurbita pepo L.), was evaluated in this study. Two different inoculation methods such as soil and seeds were used in the experiments. Disease severity, decrease rates in some plant growth parameters (leaf number, shoot length, shoot fresh and dry weight) and increases (fold) in phenolic substances in roots were assessed at 30 days after inoculation. Cvs. TG38 and Sena Hanım had the lowest disease severities when the pathogen was inoculated into soil and seeds, respectively. There were significant decreases in plant growth parameters in cultivars with high disease severity in both inoculation methods. 3,4-Dihydroxybenzoic acid is only detected in cv. Çağlayan, chlorogenic acid in cvs. Sena Hanım and TG38, and vanillic acid in cvs Çağlayan and Mert Bey, when the ethanoic root extracts of the cultivars were analyzed with high-performance liquid chromatography (HPLC). The roots of all cultivars contained syringic acid and p-coumaric acid. It was determined that p-coumaric acid increased in the roots of cvs. TG38 (7.26-fold) and Sena Hanım (6.57-fold), which showed the lowest disease severity in soil and seed inoculation methods, respectively, based on the amount of phenolic compounds compared to the control following infection. P-coumaric acid exhibited a greater antifungal effect on conidial germ tube length (EC50: 4.2 mM) of Fusarium proliferatum than on mycelial growth (EC50: 5.4 mM) and conidial germination (EC50: 46.0 mM). The results of this study indicate that p-coumaric acid may play a role in resistance of pumpkin to F. proliferatum and should be considered in pumpkin breeding studies.