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Two new Ceratocystis species cause the serious and devastating rapid ˋōhiˋa death (ROD) on native Metrosideros polymorpha in Hawaiˋi

Irene Barnes: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div>New reports of <em>Ceratocystis</em> species, causing disease outbreaks on tree species globally, have increased in recent years. Some of the most aggressive <em>Ceratocystis</em> spp. recently emerging as serious threats to trees include <em>C. manginecans</em> on plantation-grown <em>Acacia</em> <em>mangium</em> in South East Asia, and <em>C. platani</em> killing <em>Platanus</em> <em>orientalis</em> in Europe. Recently, a serious new disease known as rapid ˋōhiˋa death (ROD), has emerged on native <em>Metrosideros polymorpha</em> trees in Hawaiˋi and has resulted in the death of hundreds of thousands of trees. Investigations into the causal agent of the disease revealed the presence of two novel <em>Ceratocystis</em> species. Based on a combination of the morphological, phylogenetic and biological species concepts, these fungi have been described as <em>Ceratocystis lukuohia</em> residing in the Latin American Clade, and <em>Ceratocystis huliohia</em> residing in the Asian-Australian Clade of <em>Ceratocystis senu lato</em>. <em>Ceratocystis lukuohia</em> is most closely related to isolates from <em>Syngonium</em> and <em>Xanthosoma</em> from the Caribbean and other regions (including Hawaiˋi), and <em>C. platani,</em> which is native to eastern USA. <em>Ceratocystis</em> <em>huliohia</em> is most closely related to the newly described species of <em>C. uchidae</em>, <em>C. changhui</em> and <em>C. cercfabiensis</em>, which are considered to be native to Asia. Screening of the isolates with microsatellite markers suggests that both species are clonal in Hawai’i and are likely recently introduced pathogens. This disease threatens a native tree species which is of ecological, cultural and biological significance to Hawaiˋi. The serious nature of the disease highlights the need for an integrative management approach to prevent the spread of both pathogens, which are currently restricted to the Big Island.</div>