Ferulic acid increases the disease resistance of apples

Apple (Malus domestica Borkh.) fruit provides abundant nutritional substances and functional ingredients as one of the most popular horticultural products (Feng et al., 2021). However, apples are vulnerable to Penicillium expansum after harvest which results in tremendous postharvest losses and generates patulin in the tissues (Wang et al., 2021). In recent years, induced resistance, as an environmentally friendly and broad-spectrum approach, has received increasing attention in controlling postharvest decay of fruit (Romanazzi et al., 2016). Studies manifested that acibenzolar-S-methyl (ASM) (Wei et al., 2019, Li et al., 2020), epicatechin (Zhang et al., 2020), caffeic acid (Zhang et al., 2020, Huang et al., 2022a), ?-poly-L-lysine (?-PL) (Ge et al., 2018a, Dou et al., 2021), ?-aminobutyric acid (GABA) (Gur et al., 2021, Zhu et al., 2022), Sporidiobolus pararoseus Y16 (Zhao et al., 2018), and Meyerozyma guilliermondii (He et al., 2020) enhanced disease resistance against blue mold, gray mold and Alternaria rot of postharvest apple fruit. Ferulic acidFerulic acid (4-hydroxy-3-methoxycinnamic acid) is synthesized by phenylpropanoid pathway and plays pivotal roles in cross-linking of cell wall, antisepsis and defense responses in plants (Zdu?ska et al., 2018, Hern?ndez et al., 2021). Researches indicated that ferulic acid treatment reduced the incidence of apples and tomatoes inoculated with Botrytis cinerea (He et al., 2019, Shu et al., 2021). A study manifested that ferulic acid impaired the membrane integrity and inhibited the growth of Alternaria alternata to control postharvest disease of pear fruit (Kong et al., 2023). In addition, ferulic acid alone or with p-coumaric acid can decrease the postharvest losses and improve the storage ability of peaches (Hern?ndez et al., 2021). These findings manifest that ferulic acid can be regarded as a potentially natural inducer to prime disease resistance in horticultural products. Inducing disease resistanceStudies have proven that phenylpropanoid pathway and reactive oxygen species (ROS) metabolism participated in inducing disease resistance in vegetables and fruit (Cheng et al., 2020, Guo et al., 2023). Non-enzymatic antioxidants containing reduced glutathione (GSH) and ascorbic acid (AsA) as well as antioxidant enzymes regulate ROS level in plants (Meitha et al., 2020). A study revealed that ?-PL enhanced peroxidase (POD) and catalase (CAT) activities and gene expressions to control blue mold of postharvest apples (Dou et al., 2021). Researches have evidenced that GABA and ASM activated the gene expressions and activities of glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and ascorbate peroxidase (APX) to increase GSH and AsA contents in apples, contributing to heighten fruit resistance against P. expansum (Cheng et al., 2020, Zhu et al., 2022). A study manifested that ferulic acid promoted POD activity and decreased hydrogen peroxide (H2O2) content to inhibit gray mold in ?Pink Lady? apples (He et al., 2019). Studies in apples have also proven that ?-PL, sodium nitroprusside (SNP), and sodium hydrosulfide (NaHS) activated 4-coumarate coenzyme A ligase (4CL), cinnamate-4-hydroxylase (C4H), and phenylalanine ammonia-lyase (PAL) activities to promote flavonoids, lignin, and phenolic compounds accumulation, thus enhancing fruit resistance against P. expansum (Ge et al., 2018a, Ge et al., 2019a, Deng et al., 2021). Ferulic acid increased PAL, cinnamyl alcohol dehydrogenase (CAD), and POD activities as well as PAL and C4H expressions to strengthen resistance against B. cinerea in tomatoes and apples (He et al., 2019, Shu et al., 2021). However, to our knowledge, the relationship between ROS metabolism, phenylpropanoid pathway, and disease resistance in ferulic acid-treated apples are still unclear. Aims of the studyThis study evaluated the impacts of ferulic acid on the growth of P. expansum in vivo and in vitro, the gene expressions and enzyme activities as well as the metabolites contents involved in ROS metabolism and phenylpropanoid pathway in apples. AbstractPostharvest decay of fruit caused by phytopathogen often causes tremendous losses during logistics. Ferulic acid is a kind of phenolic acid which has potential antimicrobial ability and initiates defense responses. This study performed to evaluate the induced resistance of ferulic acid against blue mold of apples (cv. Qiujin) as well as the mechanism involved in its action. Results suggested that 1.0 g L?1 ferulic acid remarkably reduced lesion diameter of Penicillium expansum-inoculated apples and colony diameter in vitro. The activities and gene expressions of catalase, superoxide dismutase, peroxidase, dehydroascorbate reductase, glutathione reductase, monodehydroascorbate reductase, ascorbate peroxidase, and nicotinamide adenine dinucleotide phosphate oxidase were distinctly improved by ferulic acid immersion. Ferulic acid also promoted ascorbic acid and reduced glutathione contents, whereas decreased hydrogen peroxide and malondialdehyde contents in apples. Moreover, ferulic acid enhanced the gene expressions and activities of cinnamyl alcohol dehydrogenase, 4-coumarate coenzyme A ligase, cinnamate-4-hydroxylase, and phenylalanine ammonia-lyase, resulting in caffeic acid, flavonoids, lignin, total phenolics, and p-coumaric acid accumulation in apples. Taken together, ferulic acid could activate the activities and gene expressions of the key enzymes in phenylpropanoid pathway as well as reactive oxygen species metabolism to promote the synthesis of antioxidants and secondary metabolites, thereby increasing disease resistance of apples. SourcesFerulic acid enhanced resistance against blue mold of Malus domestica by regulating reactive oxygen species and phenylpropanoid metabolismMi Guo, Canying Li, Rui Huang, Linhong Qu, Jiaxin Liu, Chenyang Zhang & Yonghong GePostharvest Biology and Technology, Volume 202, August 2023, 112378https://doi.org/10.1016/j.postharvbio.2023.112378 Picture is the graphical abstract of the paper