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Abstract
Phomopsis longanae Chi is a major pathogenic fungus that infects harvested longan fruit. This study aimed to investigate the effects of P. longanae on reactive oxygen species (ROS) metabolism and its relation to the pericarp browning and disease development of harvested longan fruit during storage at 28°C and 90% relative humidity. Results showed that compared to the control longans, P. longanae-inoculated longans displayed higher indexes of pericarp browning and fruit disease, higher O2-. generation rate, higher accumulation of malondialdehyde (MDA), lower contents of glutathione (GSH) and ascorbic acid (AsA), lower 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability and reducing power in pericarp. In addition, P. longanae-infected longans exhibited higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the first 2 days of storage, and lower activities of SOD, CAT, and APX during storage day 2–5 than those in the control longans. These findings indicated that pericarp browning and disease development of P. longanae-infected longan fruit might be the result of the reducing ROS scavenging ability and the increasing O2-. generation rate, which might lead to the peroxidation of membrane lipid, the loss of compartmentalization in longan pericarp cells, and subsequently cause polyphenol oxidase (PPO) and peroxidase (POD) to contact with phenolic substrates which result in enzymatic browning of longan pericarp, as well as cause the decrease of disease resistance to P. longanae and stimulate disease development of harvested longan fruit.
Highlights
Longan (Dimocarpus longan Lour.) is a popular tropical fruit famous for its appealing flavor and abundant nutritional ingredients (Lin et al, 2001; Chen et al, 2015)
The fruits were stored under the same storage condition of 28◦C and 90% relative humidity. 150 fruits (3 bags) from each treatment were randomly selected at each storage day to determine the physiological and biochemical indexes and their relations to longan pericarp browning and disease development caused by P. longanae (Chen et al, 2018a)
The O2−. generation rate was higher (P < 0.05) in postharvest longans inoculated by P. longanae compared to the control longans during 1–5 days of storage
Summary
Longan (Dimocarpus longan Lour.) is a popular tropical fruit famous for its appealing flavor and abundant nutritional ingredients (Lin et al, 2001; Chen et al, 2015). Researches indicated that pericarp browning of postharvest longan fruit was mainly due to the formation of browning substances resulting from enzymatic browning (Wang et al, 2015; Lin et al, 2017b). Reactive oxygen species (ROS), such as superoxide anion (O2−.)and hydrogen peroxide (H2O2), was reported to cause pericarp browning of fruits (Shah et al, 2017). Overaccumulation of ROS could lead to peroxidation of membrane lipid, loss of compartmentalization of cells and organelles, and formation of browning substances when peroxidase (POD) and polyphenol oxidase (PPO) contact with phenols (Lin Y.F. et al, 2016; Lin et al, 2017a; Sun et al, 2018). Plant cells contain non-enzymatic endogenous antioxidant substances, including glutathione (GSH) and ascorbic acid (AsA) (Sun et al, 2018)
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