| Summary: | Soursop fruit (<i>Annona muricata</i> L.) production is diminished by the attack of pathogens such as <i>Nectria haematococca</i>. However, the fruit–pathogen interaction at the biochemical and molecular levels is still unknown. The objective of this study was to analyze the response of the soursop fruit to the presence of <i>N. haematococca</i> during postharvest storage. Soursop fruits were inoculated with the pathogen and total phenolic compounds, antioxidant capacity by Ferric reducing/antioxidant power (FRAP), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS•+), and 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH•), as well as enzymatic activity and transcript levels of <i>polyphenol oxidase (PPO)</i> and <i>superoxide dismutase (SOD),</i> were evaluated at 1, 3, and 5 days of storage. The noninoculated fruits were the controls of the experiment. The highest total phenol content was recorded on day one in the inoculated fruits. FRAP, ABTS, and DPPH activity presented the highest values on day three in the control fruits. Inoculated fruits recorded the highest <i>PPO</i> activity on day five and a five-fold induction in the <i>PPO</i> transcript on day three. <i>SOD</i> activity showed a decrease during the days of storage and 10-fold induction of <i>SOD</i> transcript on day three in the inoculated fruits. Principal component analysis showed that total phenols were the variable that contributed the most to the observed variations. Furthermore, a positive correlation between total phenols and <i>SOD</i> activity, <i>PPO</i> expression, and <i>SOD</i> expression, as well as between DPPH and FRAP, was recorded. The results showed a differential response in antioxidant capacity, enzymatic activity, and gene expression during the interaction of soursop fruits–<i>N. haematococca</i> at postharvest storage.
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