In vitro and in situ Activity of Cymbopogon citratus Essential Oil Against Alternaria alternata and Phomopsis carica-papayae, Causal Agents of Papaya Leaf Diseases

Papaya cultivation is considered to be one of the most important fruit-growing activities in Cameroon, and plays a vital role in improving the livelihoods of local producers. However, leaf diseases caused by devastating fungi are a real obstacle to the development of this crop. The aim of this study was to evaluate the antifungal potential of Cymbopogon citratus essential oil against Alternaria alternata and Phomopsis carica-papayae, fungal agents associated with the deterioration of papaya leaves in the Moungo region of Cameroon. The essential oil of fresh C. citratus leaves was extracted by hydrodistillation. Analysis of the chemical composition by GC then GC/MS revealed Geranial (45.24%), Neral (35.57%) and Myrcene (7.21%) as the majority compounds. In vitro antifungal tests on mycelial growth by incorporation into agar gave MICs of 900 ppm and 700 ppm against A. alternata and P. carica-papayae respectively. The MIC of 700 ppm proved fungicidal on P. carica papayae, while for A. alternata the fungicidal effect was obtained at a concentration of 900 ppm. In situ, the essential oil proved significantly active in inhibiting necrosis caused by the conidial complex of the two pathogens on papaya leaves, with a percentage inhibition of 85.93% at a concentration of 6000 ppm. C. citratus EO could therefore be used as an alternative to chemical fungicides in the fight against papaya leaf disease pathogens.