Fusarium spp. diversity associated with symptomatic Acacia koa in Hawaiʽi

Fusarium spp. comprise diverse plant pathogens, which affect both agriculturally and ecologically important plant species, and harmless saprobes. Fusarium spp. inhabit widely ranging, geographic regions across the globe and can be found in soil or plant tissue in every climate type, ranging from tropical to polar regions. In their native habitats, Fusarium spp. are typically innocuous and ubiquitous soil saprophytes; however, Fusarium spp. can become devastating pathogens, especially after introduction into novel environments, where hosts are not adapted to Fusarium infection. Hawaiʽi is among the most isolated regions on Earth. Due to this isolation, many of Hawaiʽi's native plant species are not well adapted to cope with introductions of novel flora, fauna and pathogens. Pathogens, including Fusarium spp., have had a major impact on Acacia koa (koa), an iconic tree species in Hawaiʽi's forests. Multiple Fusarium spp. have been identified in association with koa, some of which have been screened for pathogenicity to koa. This study identified new associations of Fusarium spp. with koa root samples including F. verticillioides, F. redolens, F. anthophilum, F. babinda, F. commune, F. fujikuroi and F. lactis and suggests that a complex of Fusarium spp. may contribute to disease severity. Potential spread of putative pathogens across the Hawaiian Islands is suggested on the basis of haplotype network analysis.