Vicky Arlette Medzue Souop Kamga¹, Moïse Ntah A Ayong¹, Christian Fokam Talla¹, Kamsu Noumegna Pamela¹, Séverin Nguemezi Tchameni^1,, Pierre Michel Dongmo Jazet¹

In subtropical countries, black pod caused by Phytophthora megakarya is one of the main diseases causing drastic losses of cocoa. The synthetic chemicals used to control the pathogen, although effective, could be harmful to Human and environment. The use of natural substances such as essential oils (EO) is necessary. This work aimed to determine the chemical composition of thyme essential oil and its antimicrobial potential against Phytophthora megakarya. Essential oil was extracted by hydrodistillation and the chemical composition was analyzed by gas chromatography couple to mass spectrometry (GC/MS). The evaluation of the antimicrobial activity was done in vitro by agar incorporation and liquid dilution. In situ tests were carried out by spraying the EO on the cocoa cortex after and before infected by the pathogen respectively, for the preventive test and curative healing. Results showed that, the yield of thyme EO was 0.42% with thymol (32.41%), ƴ-terpinene (19.65%) and p- cymene (19.43%) as major components. At 225µl/l, the oil completely inhibited the mycelial growth of P. megakarya while at 400µl/l this oil completely inhibited the germination of zoospores. At 1125 µl/l, thyme EO completely inhibited the necrosis on cocoa pods for preventive test. At the same concentration, the oil significantly reduced (40 %) the necrosis during the curative healing. There was significant correlation between EO concentration and the necrosis formation. These results showed that, thyme essential oil could be used as alternative to fight against black pod disease. However, the formulation of oil and fields essay are needed.

Theobroma cacao, Cocoa black pod, Phytophthora megakarya, Essential oil, Thymus vulgaris