Phenolic compounds suppress anthracnose decay by enhancing antifungal properties and biochemical defence responses in avocado fruit

Avocados are economically important fruit, however, anthracnose caused by Colletotrichum gloeosporioides affects the fruit quality during marketing. Prochloraz(R), a synthetic fungicide currently used to control this postharvest decay, is being phased out due to the hazardous toxicological properties of its metabolites. The aim of this study was to investigate the effect of five phenolic compounds (caffeic, vallinic, coumaric, gallic, and ferulic acids) on the inhibition of radial mycelial growth and spore germination of C. gloeosporioides in vitro, as well as on the incidence of anthracnose and defence-related enzymes in fruit inoculated with C. gloeosporioides in vivo during postharvest storage. Complete inhibition of the radial mycelial growth and spore germination of C. gloeosporioides was obtained with caffeic acid and vanillic acid, both at 700 mg/L. Thereafter, Fuerte avocado fruit were inoculated with C. gloeosporioides, treated with 700 mg/L caffeic acid and vanillic acid and stored for 28 days at 6.5 oC for 18 days at 85% RH, and afterwards held at 25 oC for 5 days. The caffeic acid and vanillic acid (700 mg/L) treatments significantly reduced the anthracnose incidence compared to the Prochloraz(R) treated or untreated control fruits. Caffeic acid and vanillic acid (700 mg/L) treatment enhanced the activities of chitinase, 1,3-beta-glucanase, phenylalanine ammonia-lyase and peroxidase with a concomitant increase in exocarp epicatechin. This suggests that the effects of vanillic and caffeic acids on anthracnose incidence in the avocado fruit are due to the antifungal activities and elicitation of biochemical defence responses in the fruit.

Automated summary

This study found that caffeic acid and vanillic acid have complete inhibitory effects on the growth and germination of C. gloeosporioides in vitro. During postharvest storage, the treatments of caffeic acid and vanillic acid significantly reduced the incidence of anthracnose and increased the activities of defense-related enzymes in the fruit.