Evaluation of efficacy of four Cinnamomum species extracts and cinnamaldehyde to control anthracnose of mango fruit

Anthracnose of mango is one of the major postharvest diseases of mango fruit caused by members of the Colletotrichum gloeosporioides species complex such as Colletotrichum siamense. Crude extracts from dry trunk bark of four Cinnamomum species (C. burmanni, C. iners, C. loureiroi, and C. verum), a commercial cinnamon powder, cinnamaldehyde, eugenol, and cinnamon oil were assayed for their antifungal activity against Colletotrichum siamense. The crude extract of C. verum at 500 mg L⁻¹ showed the highest inhibition of mycelial growth. At a concentration above 10 g L⁻¹ cinnamaldehyde, eugenol, and cinnamon oil showed 100% mycelial inhibition. Using the microdilution assay, C. burmanni and C. verum crude extracts were effective against Colletotrichum siamense spore germination and showed a minimum inhibitory concentration (MIC) value of 625 mg L⁻¹ while the MIC value of cinnamaldehyde was 50 mg L⁻¹. The direct bioautography of the C. verum extract and the fractions obtained by column chromatography over silica gel against Cladosporium herbarum revealed clear inhibition zones on TLC plates. The treatment of Colletotrichum siamense spores with this active fraction led to severe membrane damage which was observed by scanning electron microscopy. Comparative HPLC analyses of the Cinnamomum extracts and the active fraction of C. verum, cinnamon power, and the cinnamaldehyde and eugenol as standards indicated cinnamaldehyde as the major compound. The C. verum fraction reduced disease severity and disease incidence on inoculated mango fruit. Moreover, uninoculated mango dipped into C. burmanni and C. verum extracts reduced the naturally occurring disease while total soluble solid, titratable acidity, and weight loss of dipped mango were insignificantly different from the untreated fruit control.