Visualization of the Infection and Colonization Process of Dendrobium officinale Using a Green Fluorescent Protein-Tagged Isolate of Fusarium oxysporum.

Abstract

Dendrobium officinale soft rot is a widespread and destructive disease caused by Fusarium oxysporum that can seriously affect its yield and quality. To better understand the fungal infection and colonization, we successfully created an F. oxysporum labeled with green fluorescent protein (GFP) using Agrobacterium tumefaciens-mediated transformation (ATMT) method. Transformants had varying fluorescence intensities, but their pathogenicity did not differ from that of the wild type (WT). Fluorescence microscopy revealed that F. oxysporum primarily entered the aboveground portion of D. officinale through the leaf margin, stomata, or by direct penetration of leaf surface. It then colonized the mesophyll and spreads along its vascular bundles. After 14 d of culture, D. officinale exhibited typical symptoms of decay and wilting, accompanied by a pronounced fluorescence signal in the affected area. The initial colonization of F. oxysporum in the subterranean region primarily involved attachment to the root hair and epidermis, which progressed to the medullary vascular bundle. At 14 days post inoculation (dpi), the root vascular bundles of D. officinale exhibited significant colonization by F. oxysporum. Macroconidia were also observed in black rot D. officinale tissue. In particular, the entire root was surrounded by a significant number of chlamydospore-producing F. oxysporum mycelia at 28 dpi. This approach allowed the visualization of the complete infection process of F. oxysporum and provided a theoretical foundation for the development of field control strategies.