Ultrastructural study of conidia of Colletotrichum gloeosporioides and Colletotrichum musae treated with essential oils.

Abstract

SUMMARY Essential oils have shown to be efficient in the control of plant diseases; however, no reports exist regarding their mode of action on plant pathogens. The aim of this work was to evaluate the effect of essential oils from Cymbopogon martinii, Eugenia caryophyllata, Thymus vulgaris, Cinnamomum sp. and Cymbopogon citratus on conidia of Colletotrichum gloeosporioides and Colletotrichum musae, etiologic agents of anthracnose of guava and banana, respectively, by means of transmission electron microscopy (TEM). Conidia suspensions (1×10 10 conidia/ml) prepared in sterile distilled water with Tween 20® 1.0% were treated with essential oils at 0.5%, remaining under agitation at 25°C for 24h. Water alone was used as control. After centrifugation the supernatant was discarded and the masses of conidia obtained were fixed for 24h in modified Karnovsky fixative. The suspensions were centrifuged again and af ter discarding the supernatant, the fixed conidia were embedded in agarose gel and subjected to the protocol of sample preparation for TEM, to be observed with a Zeiss EM 109 microscope. The essential oils showed fungitoxic action directly on the conidia of C. gloeosporioides and C. musae, causing severe damage by promoting cellular disorganization and degradation that makes germination unviable.