HILO, Hawai'i — Scientists are trying to determine if some koa trees have a natural resistance to koa wilt, a disease caused by fungus that attacks and sometimes kills the prized hardwood seedlings and trees.

If experts can confirm that some trees are genetically resistant to the fungus, that could be the first step in developing a resistant population of koa.

If experts can confirm that some trees are genetically resistant to the fungus, that could be the first step in developing a resistant population of koa.

According to the Agricultural Research Center, formerly known as the Hawaiian Sugar Planters' Association, there is good reason to believe some koa families have a natural resistance to the disease.

Even in stands of badly infected trees, some grow well and show no sign of the disease, according to research on koa wilt.

Koa wilt was first identified in 1980 and has been found on all of the four major islands in Hawai'i. It has damaged native forests as well as koa plantations around the state.

Badly infected plantations may lose 90 percent of their trees, according to researchers Nicklos Dudley and J.B. Friday.

The range of the disease has increased as former canefields are replanted in koa.

Now researchers plan to ship root, stem and branch samples of infected koa trees to a laboratory in Idaho, where scientists will isolate the fungus that causes the disease.

The fungus removed from the ailing trees will be shipped back to Hawai'i Agricultural Research Center facilities on O'ahu. Koa seedlings will be dosed with the fungus in greenhouse tests to try to identify resistant seedlings, according to an application filed with the state Department of Agriculture by Dudley, a research center forester.

The project is a combined effort by the research center; the Division of Forestry and Wildlife, state Department of Land and Natural Resources; and the U.S. Forest Service. The state Department of Agriculture last month approved the application to re-import the fungus for the tests.

Scientists aren't sure whether koa wilt evolved in Hawai'i or whether it arrived with other trees, such as the Formosan koa that it also attacks, according to the Hawai'i Agricultural Research Center.

The fungus enters the trees through the roots and moves up through the stem and branches, blocking to flow of moisture to the leaves. That causes stunting and wilting, and the infected trees then become vulnerable to other pests.

Trees less than 15 years old seem to be affected more than older trees. The sickly trees quickly lose their canopies and may die within a few months. Trees at elevations below 2,500 feet also appear to be more vulnerable.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.