First report of ceratocystis lukuohia on Metrosideros polymorpha on the island of Kaua'i, Hawai'i

Authors: BRILL, EVA - University Of Hawaii; HUGHES, MARC - University Of Hawaii; HELLER, WADE - University Of Hawaii; Keith, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2019
Publication Date: 10/20/2019
Citation: Brill, E., Hughes, M.A., Heller, W.P., Keith, L.M. 2019. First report of ceratocystis lukuohia on Metrosideros polymorpha on the island of Kaua'i, Hawai'i. Plant Disease. 49(5). https://doi.org/10.1111/efp.12546.
DOI: https://doi.org/10.1111/efp.12546

Interpretive Summary: Ceratocystis lukuohia is one of two newly discovered tree pathogens causing rapid ‘ohi‘a death. C. lukuohia was recently detected on Kaua‘i, which is the first report of it beyond Hawai‘i Island.

Technical Abstract: ‘Ohi‘a (Metrosideros polymorpha) is the dominant and most ecologically and culturally important native tree in the Hawaiian Islands. Rapid ‘Ohi‘a Death (ROD), a lethal disease complex caused by the fungi Ceratocystis lukuohia and C. huliohia I. Barnes, T.C. Harrin. & L.M. Keith, has caused widespread ‘ohi‘a mortality across Hawai‘i Island (Barnes et al. 2018). In December 2018, UAV surveys on the Island of Kaua‘i detected three ‘ohi‘a trees near the Anahola mountain range that had completely wilted crowns with brown leaves attached. Inspection of the outer sapwood using a hatchet revealed a brown to black discoloration typical of ROD. Wood samples from the three trees were collected from discolored portions of the sapwood using a flame-sterilized drill bit and mailed to the USDA ARS facility in Hilo for testing using a diagnostic qPCR assay developed by Heller and Keith (2018); C. lukuohia DNA was detected in all samples tested. Carrot baiting (Moller and Devay 1968) was used to recover the fungus from infected wood tissue of all three trees. A single perithecium per sample was aseptically transferred to 10% V8 agar and the cultures looked identical to C. lukuohia isolates collected from Hawai‘i Island. PCR amplification and sequencing of the ITS region of rDNA, ß-tubulin (tub2), and cerato-platanin loci were carried out for one isolate, P19-12. BLASTn analyses of the sequence data (GenBank Accession Nos. MK863991, MK863992, MK863993) showed that the isolate was 100% identical to C. lukuohia P14-1-1 (KP203957/ITS; KU043263/tub2; KU043257/cerato-platanin). To confirm pathogenicity, five ‘ohi‘a seedlings (mean height = 0.6 m) were inoculated with filter paper discs soaked in a 1.2 x 106 spore/ml suspension following the method of Keith et al. (2015). Control plants were inoculated with filter discs soaked in water. All plants were held in a growth chamber set to 24°C (12 hr light) and the experiment was conducted twice. Within four weeks post-inoculation 7 of 10 seedlings wilted and died. All dead seedlings were dissected and stained xylem tissue was evident throughout the plants. In addition, the three remaining asymptomatic seedlings contained stained xylem 15 to 21 cm above the inoculation points. C. lukuohia was successfully reisolated and identified molecularly from all 10 plants, thus completing Koch’s postulates. All control plants remained healthy and the fungus was not recovered on carrot baits. To our knowledge, this is the first report of C. lukuohia beyond Hawai‘i Island. Although further work will be necessary to assess the impact of ROD on Kaua‘i, the results reported here expand the known geographic range of C. lukuohia. The discovery of C. lukuohia on Kaua‘i is of great concern, both for the health and proliferation of ‘ohi‘a on that island as well as neighboring islands such as Mau‘i and O‘ahu.