Anthracnose caused by Colletotrichum gloeosporioides is a major postharvest disease in avocados that
causes significant losses during transportation and storage. Complete inhibition of the radial mycelia
growth of C. gloeosporioides in vitro was observed with citronella or peppermint oils at 8 L plate−1
and thyme oil at 5 L plate−1. Thyme oil at 66.7 L L−1 significantly reduced anthracnose from 100%
(untreated control) to 8.3% after 4 days, and to 13.9% after 6 days in artificially wounded and inoculated
‘Fuerte’ and ‘Hass’ fruit with C. gloeosporioides. GC/MS analysis revealed thymol (53.19% RA), menthol
(41.62% RA) and citronellal (23.54% RA) as the dominant compounds in thyme, peppermint and citronella
oils respectively. The activities of defence enzymes including chitinase, 1, 3--glucanase, phenylalanine
ammonia-lyase and peroxidase were enhanced by thyme oil (66.7 L L−1) treatment and the level of
total phenolics in thyme oil treated fruit was higher than that in untreated (control) fruit. In addition,
the thyme oil (66.7 L L−1) treatment enhanced the antioxidant enzymes such as superoxide dismutase
and catalase. These observations suggest that the effects of thyme oil on anthracnose in the avocado
fruit are due to the elicitation of biochemical defence responses in the fruit and inducing the activities of
antioxidant enzymes. Thus postharvest thyme oil treatment has positive effects on reducing anthracnose
in avocados.
© 2013