<jats:title>Summary</jats:title><jats:p><jats:italic><jats:styled-content style="fixed-case">A</jats:styled-content>lternaria</jats:italic> species produce and excrete dimethyl coprogen siderophores to acquire iron. The <jats:italic><jats:styled-content style="fixed-case">A</jats:styled-content>lternaria alternata</jats:italic> gene <jats:italic><jats:styled-content style="fixed-case">AaNPS6</jats:styled-content></jats:italic>, encoding a polypeptide analogous to fungal nonribosomal peptide synthetases, was found to be required for the production of siderophores and virulence on citrus. Siderophores purified from culture filtrates of the wild‐type strain did not induce any phytotoxicity on the leaves of citrus. Fungal strains lacking <jats:italic><jats:styled-content style="fixed-case">AaNPS6</jats:styled-content></jats:italic> produced little or no detectable extracellular siderophores and displayed an increased sensitivity to <jats:styled-content style="fixed-case">H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub></jats:styled-content>, superoxide‐generating compounds (<jats:styled-content style="fixed-case">KO<jats:sub>2</jats:sub></jats:styled-content> and menadione) and iron depletion. Δ<jats:italic>nps6</jats:italic> mutants were also defective for the production of melanin and conidia. The introduction of a wild‐type <jats:italic><jats:styled-content style="fixed-case">AaNPS6</jats:styled-content></jats:italic> under the control of its endogenous promoter to a Δ<jats:italic>nps6</jats:italic> null mutant at least partially restored siderophore production and virulence to citrus, demonstrating a functional link between iron uptake and fungal pathogenesis. Elevated sensitivity to <jats:styled-content style="fixed-case">H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub></jats:styled-content>, seen for the Δ<jats:italic>nps6</jats:italic> null strain could be relieved by exogenous application of ferric iron. The expression of the <jats:italic><jats:styled-content style="fixed-case">AaNPS6</jats:styled-content></jats:italic> gene was highly up‐regulated under low‐iron conditions and apparently controlled by the redox‐responsive yeast transcriptional regulator <jats:styled-content style="fixed-case">YAP1</jats:styled-content>. Hence, the maintenance of iron homeostasis via siderophore‐mediated iron uptake also plays an important role in resistance to toxic reactive oxygen species (<jats:styled-content style="fixed-case">ROS</jats:styled-content>). Our results demonstrate further the critical role of <jats:styled-content style="fixed-case">ROS</jats:styled-content> detoxification for the pathogenicity of <jats:italic><jats:styled-content style="fixed-case">A</jats:styled-content>. alternata</jats:italic> in citrus.