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 applefruit, respectively. These wound pathogens can infect through injuries caused during harvest and posthar-vest handling, which lead to large economic losses. Susceptibility of fruit to mechanical damage orinfection increases during ripening. However, few studies have been focussed on the fruit wound-induceddefence responses, such as H2O2production. In this study, the characterisation of H2O2production inorange (C. sinensis cv Valencia) and apple (M. domestica L. cv Golden Smoothee) fruit in response toabiotic (wounding) and biotic (pathogen and non-host pathogen) stresses at different maturity stageswas investigated. The effect of H2O2on the ecophysiology of P. digitatum and P. expansum at differenttemperatures was also studied. The potential antifungal effect of H2O2in both pathogens depends onthe temperature. P. expansum was more susceptible to higher levels of H2O2than P. digitatum, espe-cially at 25◦C. The lesion diameter in compatible interactions increased significantly with fruit maturityin 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. H2O2production showeddifferent patterns depending on the fruit. In apples, the higher resistance of immature harvested fruit topathogen infection correlated with an increase in H2O2production (biphasic oxidative burst), whereasin oranges, immature and commercial harvests exhibited a similar pattern of H2O2production amongtreatments. Production of H2O2in oranges and apples following abiotic (wounding) and biotic (pathogenand non-host pathogen) stresses depended on the harvest date.