Inhibitory activity of 20 oomycetes fungicides against Phytophthora capsici in Wanning City of Hainnan Province

Black pepper (Piper nigrum L.) is an important tropical cash crop in China and suffers huge economic losses every year due to foot rot disease. In order to clarify the pathogen in black pepper main producing area and screen potential fungicides for disease control. Seven strains were isolated from Wanning City of Hainan Province and identified by morphological characteristics and ITS sequence specificity. The laboratory toxicities of 20 fungicides, registered for the control of oomycete diseases, were determined by the mycelial growth rate method. Results showed that all three strains isolated from black pepper foot rot disease samples, were Phytophthora capsici. Among the 20 tested oomycete fungicides, pyraclostrobin, fluazinam, thiram, dimethomorph, cyazofamid, and metalaxyl showed the highest activity in suppressing the mycelial growth of three P. capsici isolates (EC₅₀ < 1 μg/mL), followed by oxine-copper, chlorothalonil, mancozeb, zineb, copper hydroxide (1 μg/mL < EC₅₀ < 10 μg/mL), and then cuprous oxide, copper oxychloride, azoxystrobin, carvacrol, cymoxanil, berberine (10 μg/mL < EC₅₀ < 50 μg/mL). Chitosan and fosetyl-aluminium exhibited the lowest inhibition activity (EC₅₀ > 300 μg/mL). This study would help further the understanding and management of tropical P. capsici diseases.