Framework for establishing a Rapid 'Ohi'a Death resistance program

Metrosideros polymorpha Gaud. ('ohi'a) is the most abundant native forest tree in Hawai'i and a keystone species of cultural, ecological, and economic importance. However, stands of M. polymorpha are being severely impacted by Rapid 'Ohi'a Death (ROD), which is characterized by branch dieback, crown wilting, and mortality. Research revealed that ROD is caused by two novel species of Ceratocystis pathogens that cause two distinct diseases: C. lukuohia and C. huliohia. Initial disease resistance screening of four varieties of M. polymorpha with C. lukuohia demonstrated that varieties may differ in susceptibility. Several survivors of field or screening-based infections still exist, providing strong impetus for the establishment of the 'Ohi'a Disease Resistance Program (ODRP). We propose a framework for guiding the ODRP throughout the process of identifying and developing ROD resistance in M.polymorpha and, possibly, all Hawaiian Metrosideros species. Core ODRP projects include: i) evaluating and operationalizing methods for greenhouse-based production and screening of test plants; ii) greenhouse screening of seedlings and rooted cuttings sampled from native Metrosideros throughout Hawai'i; iii) establishing field trials to validate results from greenhouse assays; iv) understanding environmental and genetic drivers of resistance to characterize the durability of resistance to ROD; v) developing remote sensing and molecular methods to rapidly detect ROD-resistant individuals; and vi) conducting breeding to improve the degree and durability of ROD resistance. Ultimately, the ODRP seeks to produce ROD-resistant material for the perpetuation of M. polymorpha across Hawai'i, with the goal of preserving the ecology, culture, and communities that are dependent on this tree species.