Complexity of <i>Fusarium</i> Infections in Gladiolus: Diversity, Pathogenicity, and Fungicide Resistance

Gladiolus, a significant ornamental crop in global floriculture, frequently suffers substantial economic damage due to persistent Fusarium infections despite widespread fungicide applications. The present study systematically evaluated Fusarium diversity, pathogenicity, and fungicide resistance associated with Gladiolus crops, demonstrating the complexity in Fusarium pathogenesis. Initially, 730 Fusarium-like isolates were obtained from infected Gladiolus tissues and subsequently narrowed down to 30 isolates based on in vitro pathogenicity assays and fungicide resistance screening against carbendazim. Further selection identified 10 highly virulent isolates demonstrating resistance to carbendazim, propiconazole, and copper oxychloride. Molecular characterization using ITS and Tef1 gene sequencing classified the isolates into species complexes (SC) of Fusarium oxysporum (FOSC), Fusarium fujikuroi (FFSC), and Fusarium solani (FSSC). Isolates from the FFSC exhibited pronounced pathogenicity, with isolate GKF-6 (Fusarium circinatum) identified as the most aggressive pathogen for Gladiolus. Controlled pathogenicity assessments revealed rapid and extensive disease spread following aerial inoculation of spores, indicating that Fusarium dispersal is not limited to soil-borne mechanisms. Moreover, disease symptoms on Gladiolus plants differed with the mode and time of infection. These critical observations, along with the demonstrated fungicide resistance and genetic diversity of Fusarium isolates, highlight the necessity of revisiting current disease management strategies heavily reliant on fungicides.