First report of different mating types of Phytophthora infestans isolates from potatoes in Cameroon and their control using Thevetia peruviana (Pers.) K. Schum. seeds extracts analyzed by GC–MS

Late blight caused by Phytophthora infestans, remains even now a serious disease reducing potato production and marketing in Cameroon. This work aims to evaluate the efficacy of biochemical volatiles compounds obtained by GC–MS analysis from Thevetia peruviana seeds extracts against different mating types of P. infestans isolates. P. infestans isolates from different localities in main potato producing basins of Cameroon were collected and the presence of two mating types was determined. GC–MS analysis of aqueous extracts (AqE) and methanol extracts (ME), of T. peruviana seeds was performed. Aqueous (AqE) and methanol (ME) extracts at different concentrations (6.25; 12.5 and 25 μL/mL), fungicide (F) (5.33 µL/mL) and control (C) were tested on mycelial growth and germination of three different mating types of P. infestans isolates (P2, P17 and P30). Minimal inhibition concentrations (MIC₅₀ and MIC₉₀) were evaluated. The GC–MS analysis revealed the presence of 5 and 20 compounds, respectively from AqE and ME. The most prevailing biochemical active compounds were beta-sitosterol, (86.22%) and 9,12-octadecadienoic (33.23%). Mating types A1 and A2 were present in Cameroon. AqE and ME at 25 μL/mL inhibited 100% the mycelial growth and spore germination of all mating types isolates compared to the control. The 6.25 μL/mL concentration was fungistatic, while the 12.5 and 25 μL/mL showed a fungicidal effect. The lowest MIC were 3.35 and 14.29 μL/mL for MIC₅₀ and MIC₉₀, respectively. Molecular characterization of P. infestans isolates from Cameroon is needed and T. peruviana extracts can be exploited for their biochemical volatiles compounds in a late blight control program.