Characterisation of H2O2 production to study compatible and non-host pathogen interactions in orange and apple fruit at different maturity stages

Abstract

Penicillium digitatum and Penicillium expansum are the main postharvest pathogens of orange and apple fruit, respectively. These wound pathogens can infect through injuries caused during harvest and postharvest handling, which lead to large economic losses. Susceptibility of fruit to mechanical damage or infection increases during ripening. However, few studies have been focussed on the fruit wound-induced defence responses, such as H2O2 production. In this study, the characterisation of H2O2 production in orange (C. sinensis cv Valencia) and apple (M. domestica L. cv Golden Smoothee) fruit in response to abiotic (wounding) and biotic (pathogen and non-host pathogen) stresses at different maturity stages was investigated. The effect of H2O2 on the ecophysiology of P. digitatum and P. expansum at different temperatures was also studied. The potential antifungal effect of H2O2 in both pathogens depends on the temperature. P. expansum was more susceptible to higher levels of H2O2 than P. digitatum, especially at 25°C. The lesion diameter in compatible interactions increased significantly with fruit maturity in apples and oranges. Fruit maturity also increased susceptibility to non-host pathogen interactions, especially reducing apple resistance to P. digitatum in the over-mature stage. H2O2 production showed different patterns depending on the fruit. In apples, the higher resistance of immature harvested fruit to pathogen infection correlated with an increase in H2O2 production (biphasic oxidative burst), whereas in oranges, immature and commercial harvests exhibited a similar pattern of H2O2 production among treatments. Production of H2O2 in oranges and apples following abiotic (wounding) and biotic (pathogen and non-host pathogen) stresses depended on the harvest date.