In Vitro Assays Suggest Rapid ‘Ōhi‘a Death Fungi Can Colonize <i>Metrosideros polymorpha</i> Fine Roots

Rapid ‘ōhi‘a death (ROD), caused by Ceratocystis lukuohia and C. huliohia, severely impacts ‘ōhi‘a lehua ( Metrosideros polymorpha), a keystone tree species on the Hawaiian Islands. This study examined the ability of these pathogens to colonize ‘ōhi‘a fine roots in a series of root dip experiments under in vitro conditions, focusing on the potential roles of host genetics and root tissue condition in susceptibility. The results showed that both pathogens can colonize and form fruiting bodies on fine roots; however, C. lukuohia had greater colonization rates and produced more perithecia than C. huliohia. Fungal colonization rates were higher in fine roots damaged by excising the root cap, suggesting that wounds enhance susceptibility. These findings suggest that fine root damage may facilitate fungal ingress, raising concerns about root infection as a potential pathway for ROD spread. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .