|HUGHES, FLINT - Us Forest Service (FS)|
|HELLER, WADE - University Of Hawaii|
|BUSHE, BRIAN - University Of Hawaii|
|FRIDAY, JB - University Of Hawaii|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2015
Publication Date: 9/1/2015
Citation: Keith, L.M., Hughes, R.F., Sugiyama, L.S., Heller, W.P., Bushe, B.C., Friday, J.B. 2015. First report of Ceratocystis wilt on `Ohi`a. Plant Disease. 99(9):1276.
Interpretive Summary: 'Ohi'a is Hawai'i’s most widespread and ecologically important native tree, defining native forest succession and ecosystem function over broad areas, providing critical habitat for rare and endangered native bird and insect species, and exemplifying the strong links between native Hawai'ian culture and the islands’ environment. Extensive 'ohi'a mortality has been observed in the Puna District of Hawai‘i Island. This is the first report of C. fimbriata causing disease in 'ohi'a, which we term Rapid 'Ohi'a Death (ROD).
Technical Abstract: 'Ohi'a (Metrosideros polymorpha Gaudich.) is Hawai'i’s most widespread native tree, occurring from sea level to 2500 m elevation in both dry and wet forests and on substrates ranging from 50 to 4 million years in age (1). It is the most ecologically important native Hawai'ian tree, defining native forest succession and ecosystem function over broad areas, providing critical habitat for rare and endangered native bird and insect species, and exemplifying the strong links between native Hawai'ian culture and the islands’ environment (2). Within the past 5 years, extensive 'ohi'a mortality has been observed in the Puna District of Hawai‘i Island in apparently healthy trees growing in undisturbed forest settings. Affected trees exhibit rapid (i.e., within weeks), synchronized death of leaves on individual branches that eventually spreads to the entire canopy. Dark brown to black discoloration can be seen in the woody xylem of affected trees. Branch samples displaying characteristic symptoms were collected in February, 2014 from Leilani Estates subdivision (19o28'25"N, 154o55'13"W). A perithecia-producing fungus was isolated from infected tissue, forming olive brown cultures on 10% V8 agar. After 14 days, observed perithecia were black, globose, 143 to 275 × 110 to 264 µm, and possessed a long black neck (660 to 880 µm). Ascospores were “hat” shaped, hyaline, and were 5.7 to 8.6 × 2.7 to 4.3 µm. Hyaline, cylindrical endoconidia (14.3 to 38.6 × 2.9 to 4.3 µm) were found. Based on these morphological characteristics the fungus was identified as Ceratocystis fimbriata sensu lato Ellis & Halsted (3). To confirm the identity of the pathogen, the internal transcribed spacer (ITS) region of rDNA was amplified with universal primers ITS1/ITS4 and sequenced (GenBank Accession No. KP203957), and comparisons with GenBank showed 99% similarity with C. fimbriata on diseased Syngonium sp. from Florida (Accession No. KC493164.1). Pathogenicity was tested on 1 to 2-year-old pot grown seedlings of M. polymorpha as follows. Seedlings were wounded with a scalpel to a depth of 5 mm to produce a stem flap ~50 cm above the soil level, inoculated with 2 filter paper disks soaked in a spore suspension (106 conidia per ml grown on fresh 10% V8 agar), the flap replaced and the stem wrapped with parafilm. Control plants were inoculated with filter disks soaked in sterile water. The treated plants were incubated in a greenhouse at 25 to 30°C with 55 to 60% relative humidity. Wilt symptoms caused by C. fimbriata were observed 57 to 88 days after inoculation; as the disease progressed, leaves withered and died and plant death occurred between 86 to 94 days. Internal discoloration was observed in the main stem. C. fimbriata was successfully re-isolated from the infected seedlings. All control plants remained healthy. To our knowledge, this is the first report of C. fimbriata causing disease in M. polymorpha, which we term Rapid 'Ohi'a Death (ROD). This pathogen poses a serious threat to Hawai‘i’s flagship native tree species whose loss would be catastrophic for the diversity, structure, and function of Hawai'i’s remaining native forests and the services they provide.