Postharvest management of anthracnose in avocado (Persea americana Mill.) fruit with plant-extracted oils

We tested the inhibitory properties of five different plant extracts to extend avocado fruit shelf life against anthracnose (Colletotrichum gloeosporioides Penz.). Essential oils were extracted from mint, savory, thyme, cinnamon and lavender and then analysed by gas chromatography-mass spectrometry. Carvacrol (71.2%) and thymol (73.3%) were the main components in savory and thyme. The main chemical compounds in mint oil were menthone (33.8%) and menthol (36.1%). cis-cinnamaldehyde (59.1%) was the main constituent of cinnamon oil, whereas linalyl acetate (43.1%) and linalool (26.3%) were the key compounds in lavender oil. The polymerase chain reaction (PCR) method using the internal transcribed spacer (ITS) primer confirmed the identity of the C. gloeosporiodes isolate. In-situ antifungal activity was assayed by artificially inoculating avocado fruit with C. gloeosporioides then applying essential oils to the fruit at concentrations of 0, 0.05, 0.1 or 0.2 percent. After four weeks of storage, savory and thyme oils applied at 2000 ppm exhibited the strongest antifungal activity, reducing expansion of necrotic lesions around the inoculation sites on the fruit by 58-64%. Savory and thyme oils also considerably decreased (54-67%) lesion expansion. The results of a fruit firmness assay showed that savory and thyme oils applied at 500-2000 μl L−1 resulted in fruit that were 2.5-3.3 times firmer than the non-treated controls, whereas other oils applied at 500 μl L−1 did not help maintain fruit firmness. Disease severity and fruit firmness variables were quadratically related to savory oil concentration. This study confirms the potential for using savory and thyme essential oils as biological fungicides for increasing the storage time of avocado fruit.