Exposure to oregano essential oils and lethal effect on Colletotrichum spp

Phytopathogenic fungi from Colletotrichum genus are singificant anthracnose causal agents on different plant species, in field as well as in storage. For now, in the Republic of Serbia, these pathogens are found on apples only after harvest, while their presence in field has not been registered yet. Control of storage pathogens is dififcult because in many countries use of synthetic fungicides, which are the main control tool, is prohibited after harvest. Situation in Serbia is the same and products aimed against post-harvest apple pathogenst are applied 14 days prior to harvest at the latest. To overcome this difficulty, it is neccessary to find substances with favorable ecotoxicological properties that would enable their use after harvest, prior to storage or during storage. Essential oils have high poten- tial as an alternative products for protection of apple fruits against post-harvest rots. Oregano esential oils have profound antifungal activity. Considering that essential oils are highly volatile, their lethal effect on phytopathogenic fungi has to be rapidly manifested. In this paper, minimum exposure period (MEP) of three isolates (one isolate C. gloeosporioides /AVO 374B/ and two C. acutatum isolates /MI-21 and Č-13/) to four oregano essential oils (A, B, B and D) different in origin, applied at three different rates for lethal effect achievement, has been studied. It was found that the lowest rate that causes lethal effect (0.02 μl/ml of air) has MEP of seven or more days. Higher application rates (0.04 and 0.08 μl/ml of air) have shorter MEP, and the oregano essential oil marked as C was found to be the most effective with MEP of two days for lethal effect on C. gloeosporioides and even one day for lethal effect on C. acutatum.