New Ceratocystis species associated with rapid death of Metrosideros polymorpha in Hawai`i

Abstract

The native ‘ōhi’a lehua (Metrosideros polymorpha) has cultural, biological and ecological significance to Hawai’i, but it is seriously threatened by a disease commonly referred to as rapid ‘ōhi’a death (ROD). Preliminary investigations showed that a Ceratocystis species similar to C. fimbriata s.lat. was the cause of the disease. In this study, we used a combination of the phylogenetic, morphological and biological species concepts, as well as pathogenicity tests and microsatellite analyses, to characterise isolates collected from diseased ‘ōhi’a trees across Hawai’i Island. Two distinct lineages, representing new species of Ceratocystis, were evident based on multigene phylogenetic analyses. These are described here as C. lukuohia and C. huliohia. Ceratocystis lukuohia forms part of the Latin American clade (LAC) and was most closely associated with isolates from Syngonium and Xanthosoma from the Caribbean and elsewhere, including Hawai’i, and C. platani, which is native to eastern USA. Ceratocystis huliohia resides in the Asian-Australian clade (AAC) and is most closely related to C. uchidae, C. changhui and C. cercfabiensis, which are thought to be native to Asia. Morphology and interfertility tests support the delineation of these two new species and pathogenicity tests show that both species are aggressive pathogens on seedlings of M. polymorpha. Characterisation of isolates using microsatellite markers suggest that both species are clonal and likely represent recently-introduced strains. Intensive research is underway to develop rapid screening protocols for early detection of the pathogens and management strategies in an attempt to prevent the spread of the pathogens to the other islands of Hawai’i, which are currently disease free.

The value of sentinel plants for risk assessment and surveillance to support biosecurity

“…Myrtle rust Austropuccinia psidii (G. Winter) Beenken, a pandemic neotropical rust strain associated with Myrtaceae (Carnegie and Pegg 2018) has recently established in New Zealand (Beresford et al 2018;Large and Galbraith 2017). Other emerging threats include Ceratocystis huliohia and C. lukuohia, two recently identified pathogenic strains killing the endemic ōhiʻa tree (Metrosideros polymorpha) in Hawaii (Barnes et al 2018). The obvious concern is that these strains also could have an impact on New Zealand Metrosideros species.…”

“…The probability of C. huliohia and C. lukuohia reaching New Zealand is open to conjecture. Movement of infected plant material is believed to be the main pathway for introduction and spread of these plant pathogens (Barnes et al 2018), and as no live plant material is permitted into New Zealand without a phytosanitary certificate and pre-release screening for unwanted organisms, the pathway risk appears minimal.…”

IMA Genome-F 11

“…The genus Ceratocystis includes 41 species of mainly plant pathogenic fungi (Marin-Felix et al 2017;Holland et al 2019 Barnes et al 2018;Liu et al 2018). The type species, Ceratocystis fimbriata, was first described in the USA in 1890 as the causal agent of black rot of Ipomoea batatas (Halsted 1890).…”

Fungi infecting woody plants: emerging frontiers

“…( Ploetz et al 2013 , Tsopelas et al 2017 ). In this volume, Barnes et al (2018) describe a new disease that is rapidly assuming crisis status in Hawai’i and that has colloquially been termed Rapid ‘ôhi’a death (ROD). The disease has resulted in the death of hundreds of thousands of native Metrosideros polymorpha trees on the Big Island of Hawai’i ( Mortenson et al 2016 ).…”

“…The pathogen responsible for the wilt symptoms was tentatively identified as C. fimbriata s.lat., and the disease was referred to as Ceratocystis wilt ( Keith et al 2015 ). However, results of a morphological and phylogenetic study by Barnes et al (2018) have shown that two new Ceratocystis species, C. lukuohia and C. huliohia , are associated with ROD. Morphology and interfertility tests support the delineation of these new species and pathogenicity tests have shown that both taxa are pathogens although their relative importance has yet to be determined.…”