The effect of elevated CO2 levels on the symptom expression of Colletotrichum gloeosporioides on avocado fruits

Exposure of freshly harvested avocado fruits to different concentrations of CO₂ (11, 16 and 30%) for different lengths of time (4, 17 and 26 h) affected the decay development caused by Colletotrichum gloeosporioides. The delay in symptom development depended on the treatment given, the temperature regime of the fruit and time after harvest for treatment application. The most appropriate treatment was the application of 30% CO₂ for 24 h at a temperature of 20-25 C on the day of harvest. Treatment for shorter time periods, at lower temperatures or 50 h after harvest, resulted in a reduced response and, in some cases, enhanced symptom expression. Concentrations of 11 or 16% CO₂ were less effective than 30% CO₂ as the fruits became more mature. It is concluded that treatment of avocado fruits with high levels of CO: for a short period has the potential to provide an alternative means of controlling anthracnose.