Racing against extinction: multi-method pathogen detection in a highly critically endangered New Caledonian palm

Saribus jeanneneyi is a micro-endemic New Caledonian palm on the brink of extinction with only one adult tree and few juveniles remaining. Diseases symptoms with unknown causes have been recently observed for this critically endangered species, including the adult tree. To identify the pathogens potentially involved, we used a metabarcoding approach to characterize fungal and bacterial communities in bark, leaf and root tissues from symptomatic and asymptomatic individuals. Community-level analyses showed that diseased bark harboured strongly restructured fungal and bacterial assemblages, with pronounced depletion of Cyanobacteriota and enrichment of Actinomycetota and Acidobacteriota, consistent with a shift towards a heterotrophic, stress-adapted microbiome. Heatmap-based centred log-ratio profiles and a bark-focused co-occurrence network converged on a small set of Ascomycota genera with documented plant pathogenicity (including Cyphellophora , Xenoacremonium and Gibellulopsis ) that were both enriched in symptomatic bark and centrally embedded within the interaction network, supporting a polymicrobial, fungus-dominated aetiology. In contrast, the main bacterial hubs were dominated by saprophytic or potentially beneficial taxa, suggesting roles as commensals, decomposers or antagonists rather than primary drivers of bark necrosis. These findings highlight how integrative molecular pathogen detection can rapidly pinpoint candidate pathogens and their microbial context in a critically endangered plant, and argue that conservation strategies for S. jeanneneyi should adopt a microbiome-informed approach targeting pathogenic guilds while preserving beneficial bacteria to mitigate disease risk.