This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A study led by scientists at the Holden Arboretum has found evidence that beech leaf disease (BLD) symptom development is genetically controlled, providing the first evidence that some American beech trees may have genetic resistance. This finding supports further investigation and development of breeding populations for BLD resistance.
Nearly a third of beech trees near BLD's epicenter in northeastern Ohio, the majority of which were smaller trees, have died since the disease was discovered in 2012. The new research, published in the journal Forest Pathology, was led by David Burke, vice president for science and conservation at Holden Forests & Gardens, along with Mary Mason and Jennifer Koch of the USDA Forest Service's Northern Research Station. For years, forest professionals in the region have noticed that in BLD-affected areas, not every beech shows the same severity of symptoms.
They've been documenting and monitoring trees that appear healthier in otherwise heavily symptomatic areas, building a roster of these special trees. Such trees will be conserved for use in further experiments to determine if genetic resistance to BLD can be passed from parent trees to their progeny, an essential step in developing a breeding program to create resistant trees. An existing research planting of American beech (Fagus grandifolia) at the Holden Arboretum provided a rare opportunity to test beech for genetic resistance to BLD.
The trees were established in 2005, years before BLD arrived, and had been selected, bred and tested by the USDA Forest Service for resistance to a different disease, beech bark disease. Once BLD arrived, Burke and his colleagues noticed that not all the trees were showing symptoms. "We noticed that some trees were very healthy, even though many others were looking really sick like we'd seen in the adjoining forests," Burke says.
"These trees still looked really good despite being 20 feet (6 meters) away from trees that were very clearly ill and unhealthy." Because these trees were already growing in a research planting that provided a relatively controlled, homogeneous environment—same soil, same light, same overall conditions—they suspected the differences in disease severity could be due to their underlying genetics. To test for genetic resistance, the team propagated both sick and healthier trees using cut branch tips, grafting them onto other untested seedlings (rootstock), and grew them in the greenhouse under controlled conditions. Then the team tested the trees by transferring BLD-causing nematodes, Litylenchus crenatae, into the buds.
Researchers collected nematodes by gathering infected beech leaves in the forest, cutting them open in the lab and floating them in water to extract the wormlike organisms. They counted them under a microscope to make sure every beech bud would receive the same "dose" of 100 live nematodes. The nematodes were transferred in water to beech buds in the fall.
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