Researchers hard at work to understand and stop Rapid ‘Ōhi‘a Death

Modes of transmission of the fatal fungal disease are of great concern and researchers emphasize the importance of not moving any ‘ōhi‘a trees, the chopped wood, seedlings or soil under infected trees from one area to another.

By Lara Hughes.

Tree with entire crown of dead leaves.
Symptoms of Rapid ‘Ōhi‘a Death, caused by the fungus Ceratocystis fimbriata, include rapid browning of affected tree crowns. Photo from CTAHR.

Researchers at the University of Hawai‘i at Hilo are working with the U.S. Department of Agriculture to learn more about Rapid ‘Ōhi‘a Death, a fungal disease with the potential to wipe out the indigenous tree on Hawai‘i Island and perhaps even throughout the state.

A research team at the USDA Agricultural Research Service (ARS) in Hilo, which includes a graduate student from UH Hilo, have discovered that Rapid ‘Ōhi‘a Death or ROD is being caused by more than one strain of the fungus Ceratocystis fimbriata, which they suspect can be transferred through wounds in the ‘ōhi’a trees and also through soil under infected trees.

Blaine Luiz
Blaine Luiz

Blaine Luiz, a UH Hilo graduate student in the tropical conservation biology and environmental science program, is working as a biological science technician with ARS research plant pathologist, Lisa Keith. The researchers believe that human activity contributes most to the spread of ROD, but they also are examining other possible vectors such as beetles and pigs.

“We have found evidence of spores in the mud and soil,” says Luiz. “Humans can definitely track things very far with vehicles and shoes.”

Elizabeth Stacy, professor of biology at UH Hilo who specializes in the study of evolutionary diversification of the ‘ōhi‘a genus (Metrosideros) in Hawai’i, is Luiz’s academic advisor for his master’s program. When out in the field with her own classes, Stacy asks her students to spray alcohol on their boots when going into and coming out of the forests. This helps prevent the spread of the ROD fungi and is especially important in areas where it is known to be more prevalent, such as Puna.

“Pathogenic fungi have a tremendous capacity to get around,” says Stacy.

When asked if there were other solutions to stopping the spread of ROD, Luiz referenced a tactic that has been tried on the mainland with Oak Wilt. An anti-fungal compound is injected into the trees, which helps to prevent new infections. Luiz believes that this could be useful to homeowners in the protection of the ‘ōhi’a trees on their property, but is not sure that it would work on a larger scale.

Blooming blossoms.
A healthy ‘ōhi‘a tree with blossoms. Photo Alan L.

New findings

It was previously believed that a single isolate of Ceratocystis fimbriata, a vascular wilt fungus, was the fungus responsible for the growing number of ‘ōhi‘a deaths on Hawai‘i Island, but researchers now know that there are two isolates of the fungus.

Luiz also says that there appear to be slightly different symptoms, which are currently being examined by contrasting the disease cycles of the two isolates in the laboratory at the USDA Agricultural Research Service facility in Hilo.

As far as preventative measures go, Luiz feels that the best prospect is to find naturally occurring resistance within the ‘ōhi‘a, which is part of his thesis.

Some of the trees in large die-off areas have survived, and Luiz wonders if there is something about these trees that allows them to withstand the fungi.

Stacy says, “There are four different types of ‘ōhi’a on the Big Island with different ecologies. They are differentially adapted.”

Controlling the spread

Map as of Nov. 2015. Ceratocystis has been confirmed in ʻōhiʻa samples from Volcano Village and at 5,000 ft elevation in the Wailuku River watershed. Photo from CTAHR, click to enlarge.

Certainly, if the spread of ROD continues, there is a lot to lose. Luiz points out the negative effect that the loss of ‘ōhi’a trees would have on the watershed and the augmented erosion that could occur.

The researchers emphasize the importance of not moving any ‘ōhi‘a trees, the chopped wood, seedlings, or soil near infected trees from one area to another.

“I think we can really curb the transmission,” says Luiz. “I think we’re not too late to stop this spread.”

He stresses that a lot of times the cases are found on private property, “so if it’s known that you have infected trees in the area it’s a good idea to be careful going from your home to the forest.”

Homeowners can learn about affected areas at the Hawai‘i Department of Agriculture website. The Rapid ‘Ōhi’a Death website of the College of Tropical Agriculture and Human Resources at UH Mānoa also has info and updates.

The Hawai‘i Board of Agriculture, in an attempt to stifle the transmission of ROD to other islands, recently approved an interim rule restricting the movement of ‘ōhi‘a plants, seeds, stems, green waste and logs from Hawai‘i Island. Anyone found violating this rule could be fined up to $10,000 and charged with a misdemeanor offense. More on these rules can be found at the Hawai‘i Department of Agriculture website on ‘ōhi‘a quarantine.

Overall, Luiz and Stacy seem optimistic and hope that Rapid ‘Ōhi‘a Death will soon become a memory.

“What we’re doing now is preserving what we have for the future,” says Luiz. “With fungal pathogens, it’s really difficult if we don’t know a lot about them to try and stop them. So that’s what our lab is really focused on… to try and set up ways to stop it or kill it all together, or at least prevent it from moving.”

Enjoying plant pathogen research, Luiz hopes to continue on in the field of ecology. After receiving his master of science degree, he is considering continuing on with a doctoral program, an idea his mentor, Professor Stacy, supports wholeheartedly.


About the author of this story: Lara Hughes is a junior at UH Hilo majoring in business administration. She is a public information intern in the Office of the Chancellor. 

-UH Hilo Stories