Gum Arabic-incorporated thymol/salicylic acid composite coatings control grey mould and brown rot in ‘Angeleno’ plums

Abstract

This study explores the antifungal efficacy of salicylic acid and thymol against Botrytis cinerea and Monilinia laxa, the main pathogens affecting stone fruit in South Africa. Antifungal properties of thymol and salicylic acid and their influence on the shelf life of “Angeleno” plums were investigated. Gum Arabic composite coatings infused with salicylic acid and thymol were further investigated, with fludioxonil as a positive control. In vitro, results showed complete inhibition (100%) of M. laxa and B. cinerea by thymol at 0.25 mM and 1 mM, respectively. Salicylic acid did not achieve complete pathogen inhibition The highest inhibition percentage, 38%, was recorded at 2 mM. In vivo assessments showed that while fludioxonil was highly effective, Gum Arabic coatings containing 2 mM and 4 mM salicylic acid closely matched its performance in decay prevention, reducing decay rates to 8%. Furthermore, Gum Arabic coatings significantly reduced shrivel incidence and maintained firmness of the plums over a 15 d shelf-life period. This study highlights thymol as a potent antimicrobial agent, especially against grey mould and brown rot in plums, while incorporating salicylic acid into GA coatings effectively reduces disease incidence without compromising fruit quality. These findings suggest a promising alternative to conventional fungicides in managing grey mould and brown rot in plums.