In vitro Fungitoxicity of Four Essential Oils on Sugarcane Smut Sporisorium scitamineum Piep., in Côte d'Ivoire

Abstract

Aims: Sugarcane, Saccharum officinarum (Poaceae) is an important industrial crop in Côte d’Ivoire. However, many biotic constraints such as smut du to Sporisorium scitamineum lead to yield limitation. The management of this pathogen includes thermotherapy, which is not always effective and the use of systemic fungicides which have a negative impact on human health and biodiversity. This study was to evaluate the fungitoxicity of four essential oils on Sporisorium scitamineum, in Côte d’Ivoire. Study Design: Therefore, an in vitro control trial of Sporisorium scitamineum isolates with essential oils of Ocimum gratissimum, Zingiber officinale, Cymbopogon citratus and Melaleuca quinquenervia was performed. The positive control used was propiconazole, a synthetic fungicide (triazole family). Different concentrations of the essential oils and the systemic fungicide were tested on mycelial growth and sporulation of two fungal strains S1 and S2 of Sporisorium scitamineum isolated from sugarcane varieties CP921167 and VMC93282. Place and Duration of Study: The study was performed in 2014-2015 harvest season at the sugar bowl of Ferké in Northern Côte d’Ivoire. Methodology: The effect of essential oils was compared to that of propiconazole. Thus, for the oils, 100 ml of different culture media at doses of 250, 500, 1000, 2000 and 4000 μl/l were prepared. Also, the media of propiconazole were used at four five doses (20, 25, 50, 100, 150 μl/l) prepared from 100 ml of REFERENCE, the positive control solution. The Petri dishes were incubated for 30 days, and the mycelial growth was assessed every 48hrs according to perpendicular axes at the base of each Petri dish. The radial growth measurements were used to calculate the inhibition rates of each product at the assessed doses, and the IC50 and IC90 of different assessed products were determined with ED50 plus V1.0 software. Results: The results showed that the effect of essential oils of Ocimum gratissimum and Cymbopogon citratus as well as propiconazole inhibited the mycelial growth and sporulation of both smut strains at all concentrations. The essential oil of Zingiber officinale proved to be moderately inhibitory compared to that of Melaleuca quinquenervia. Conclusion: These essential oils could be applied in vivo to assess their effect on the incidence of Sporisorium scitamineum on sugarcane cultivation with a view of a sustainable management system of sugarcane diseases, for environmental protection and human health.