MODULATION OF NATURAL-RESISTANCE OF AVOCADO FRUITS TO COLLETOTRICHUM-GLOEOSPORIOIDES BY CO-2 TREATMENT

The level of the antifungal compound, 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene, in the peel of avocado fruits decreased during ripening. Fruits exposed to a high CO2 concentration showed an initial increase in the diene level immediately after removal from CO2. The concentration of the diene then significantly decreased, before a second increase in concentration. Exposure of avocado fruits to different concentrations of CO2 (11, 16 and 30%) for different lengths of time (3, 10 and 24 h), enhanced the initial increase in diene concentration. Only 30% CO2 applied for 24 h enhanced a significant second increase in diene level and delayed symptom development caused by Colletotrichum gloeosporiodes. Fruit exposure to lower CO2 concentrations (16 and 11%) or short periods (3 and 10 h) caused no significant second increase and no significant effect on symptom development. Fruits exposed for 24 h to 30% CO2 enhanced the concentration of the phenol epicatechin in a double-peak pattern similar to that exhibited by the diene. It is suggested that CO2 treatments induce the enhancement of diene levels and consequently cause a delay in symptom development. © 1991.