The critically endangered geophyte Gladiolus aureus threatened by a wilt disease associated with Fusarium libertatis

Abstract Gladiolus aureus is a geophyte species endemic to the South African Cape Peninsula. Pressures including land-use change and invasion by alien plants have caused severe population declines, leading to its classification as Critically Endangered (CR). Kirstenbosch National Botanical Garden (NBG) maintains the largest ex situ collection of this species. During plant health surveys conducted as part of a sentinel plant research project, a recurring wilt disease was observed in the ex situ collection. Symptomatic plants were sampled and fungal isolations consistently yielded a Fusarium species, identified as F. libertatis, as confirmed through DNA sequencing and phylogenetic analyses. Dormant corms donated by Kirstenbosch NBG for pathogenicity tests were asymptomatically colonised by the same fungus, suggesting that F. libertatis may be widespread in the collection and may be moved through contaminated planting material as well as growing media. This study highlights the challenges posed by plant pathogens to the conservation of threatened plant taxa and underscores the limited disease management tools available in ex situ collections.