Correlation between the chemical composition of fresh and dried Cymbopogon citratus essential oil fractions and their antifungal effects against the causal agents of brown spot and bakanae diseases of rice

Abstract

The fresh and dried whole plant (CF and CD respectively) of Cympopogon citratus essential oils (EOs) and its fractions, were tested, for their antifungal activities against Bipolaris oryzae and Fusarium moniliforme; respectively responsible of brown spot and bakanae disease of rice (Oryzae sativa L). Their chemical compositions were obtained by GC-GC/MS analysis and correlated with their biological activities. All six collected EO fractions of C. citratus contain myrcene, limonene, α-gurjunene, neral and geranial, but in different proportions. Neral (45.64 - 79.00%) predominant in CD₁, CD₂, CD_m, CF_m, and geranial (18.79 - 45.64%) in CF₁, CF_2; were found as major components. A positive correlation between the biological activity and the predominant constituent (citral) content was not always apparent. Carvacrol acetate and farnesol (2E, 6Z) were found only in EO fractions from fresh plants (CF₁, CF₂, CF_m), and have high antifungal activity against B. oryzae and F. moniliforme compared to that of fractions from dried plants (CD₁, CD₂, CD_m). The EO fractions collected within the first 60 min starting from the moment the first drop of EO was dropped (CF₁, CD₁), were more active than the fractions collected after 61 min (CF₂, CD₂). Cedrol, hexahydrofarnesyl acetone, γ-decalactone, β-bisabolol, α-muurolol, cavacrol and β-eudesmol, were present in low amount in CF₂ and CD₂ and absent in CF₁ and CD₁. The results serve as benchmark for researchers/industries, in fast and better targeting bioactive compounds and identify plausible interactions that may exist between constituents of an essential oil for a given biological activity.