Enhanced resistance in ‘shatang’ mandarin fruit against Penicillium italicum caused by 2-methoxy-1,4-naphthoquinone

Blue mold caused by Penicillium italicum leads to considerable postharvest losses in citrus fruit. The 2-methoxy-1,4-naphthoquinone (MNQ), a natural compound from Chinese medicinal plant, had strong in vitro antifungal activity. Therefore, we investigated the in vivo effect of MNQ treatment against blue mold on ‘shatang’ mandarin fruit caused by P. italicum and the underlying mechanisms. Our results found that MNQ could suppress disease development, indicated by less severe incidence and symptoms of fruit disease. MNQ treatment maintained redox status via enhancing antioxidant enzyme activities to decrease hydrogen peroxide (H2O2) content and up-regulating sulfoxide reductase, glutaredoxin and thioredoxin gene expression to keep protein repair ability. Meanwhile, MNQ alleviated membrane damage and protein carbonylation caused by oxidative stress. Additionally, MNQ increased the activities of defense-related enzymes (phenylalanine ammonia lyase, β-1,3-glucanase and chitinase) and accumulation of lignin, phenolic compounds and flavonoids. Moreover, we found that MNQ treatment could up-regulate abscisic acid (ABA) synthetic gene expression resulting in higher ABA content. In summary, MNQ was effective as a potential agent controlling the postharvest diseases.