From Known Association to Proven Aetiology: Penicillium expansum as Postharvest Pathogen on Carrot Roots in Serbia

Abstract

Carrot is a widely cultivated root vegetable valued for its nutritional and health benefits. Carrot roots showing blue mould symptoms were collected from three locations in Serbia, and 11 fungal isolates were obtained. Representative isolates were identified using a polyphasic approach based on cultural characteristics on three media, at three incubation temperatures, multilocus sequence analysis of the internal transcribed spacer (ITS), beta-tubulin (BenA), calmodulin (CaM) and RNA polymerase II second largest subunit (RPB2), as well as phylogenetic analysis and pathogenicity test. BLASTn analysis showed 99.80–100% similarity with previously deposited sequences of Penicillium expansum for all analysed loci. Lesions developed on all inoculated roots within 7 days in pathogenicity assay. The combined results identified P. expansum as the causal agent of postharvest carrot root rot. Although this species has previously been associated with carrot spoilage, this study provides the first experimental verification of Koch's postulates worldwide, conclusively confirming P. expansum as a postharvest pathogen of carrot. Given its strong mycotoxigenic potential and broad host range, the occurrence of P. expansum on stored carrots represents a significant threat to both crop quality and food safety, highlighting the importance of routine postharvest monitoring and reliable, polyphasic diagnostic approaches.