Melatonin treatment has been reported to effectively preserve and improve the postharvest quality of fruits and vegetables during storage. This research focused on examining the significance of melatonin on maintaining the quality of fresh Gastrodia elata tubers throughout the storage period. The findings demonstrated that melatonin application effectively reduced the deterioration rate and inhibited the rise in respiratory rate, malondialdehyde content, and weight loss, while slowing down the decline in soluble solid content. Melatonin treatment led to a decrease in hydrogen peroxide production and a rise in non-enzymatic antioxidant concentrations, including ascorbic acid. Furthermore, it boosted both the activity and expression of indispensable antioxidant enzymes, like superoxide dismutase, catalase, and ascorbate peroxidase. Additionally, melatonin treatment promoted the accumulation of total phenols, flavonoids, and lignin in fresh G. elata, while enhancing both the activity and expression of critical enzymes in the phenylpropanoid pathway, including phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumarate-CoA ligase. Moreover, melatonin treatment boosted the activity and expression of energy-associated enzymes including H⁺-ATPase, succinate dehydrogenase, Ca²⁺-ATPase, and cytochrome C oxidase, contributing to the improvement of energy levels in fresh G. elata. In summary, melatonin enhances the antioxidant potential and reduces oxidative damage in fresh G. elata by activating reactive oxygen species, phenylpropanoid metabolism, and energy metabolism, thereby maintaining its postharvest quality.

Fresh Gastrodia elata tubers are highly perishable after harvest because pathogen infection accelerates quality deterioration and limits their storage and commercial utilisation. This study examined lesion development in wounded, pathogen-inoculated tubers held at 24 ± 1 °C and, in a separate experiment, quality and physiological changes in non-inoculated tubers stored at 4 ± 1 °C. In the inoculation assay, 1 mM salicylic acid (SA) reduced lesion development following inoculation with Fusarium sp. (isolate 1022-1-1) and Aspergillus sp. (isolate 1022-11). During cold storage, SA-treated tubers maintained higher soluble solid content and showed less weight loss, membrane permeability, and malondialdehyde accumulation than controls. SA application promoted the enzymatic activities and transcriptional expression of superoxide dismutase, catalase, and peroxidase. It also activated the ascorbate–glutathione cycle by promoting ascorbic acid and glutathione accumulation, along with increasing the enzymatic activities and transcript abundance of several cycle-related enzymes, including ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase. These responses limited superoxide anion production and excessive hydrogen peroxide accumulation, thereby alleviating oxidative damage. SA enhanced phenylpropanoid metabolism through the upregulation of phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, and 4-coumaroyl-CoA ligase at both enzymatic and transcriptional levels, contributing to increased levels of total phenolics, flavonoids, and lignin. Furthermore, SA contributed to ATP maintenance by upregulating hexokinase, succinate dehydrogenase, cytochrome c oxidase, H⁺-ATPase, and Ca²⁺-ATPase at both enzymatic and transcriptional levels. Overall, SA treatment reduced lesion development in inoculated G. elata tubers and helped maintain the quality of non-inoculated tubers during cold storage.