By Leah Brooks, Marketing Coordinator at Mt. Cuba Center
Today is International Day of Plant Health (IDPH), designated by the United Nations to raise global awareness about how protecting plant health can help end hunger, reduce poverty, preserve biodiversity and the environment, and boost economic development.
The decimation of native plant species through the introduction of nonnative pests and diseases provide a clear case study on the dangers of ignoring plant health. One example is the near disappearance of the American chestnut from the Eastern Deciduous Forest. The American chestnut (Castanea dentata) was a tall, fast-growing, canopy tree that grew predominantly on moist, well-drained lower slopes and on some rocky ridges. The wood is highly resistant to rot, and some stumps and logs are still evident in forests. Their nuts store well, are highly nutritious, and were once a dietary staple for humans and wildlife (a mature tree could produce up to 5 tons).
The American chestnut population was stable until 1904, when it began to decline from a fungal disease called Chestnut blight. The fungus was accidentally introduced to the U.S. via infected Japanese chestnuts (C. crenata) that had been imported for cultivation. As Japanese and Chinese chestnuts (C. mollissima) have evolved alongside the fungus, they are less susceptible to the disease. The American chestnut doesn’t have the same natural resistance and the fungus spreads unchecked within the tree. Chestnut blight girdles stems, stopping the flow of nutrients and water to the rest of the plant. The lack of nutrients results in the death of the above-ground portion of the tree, but the roots remain alive. These living roots often send up fresh shoots which may grow up to 20 ft tall, at which point the blight reinfects the shoots again and the cycle continues.
To help better understand and find ways to offset this blight, Mt. Cuba Center hosts a study site for The American Chestnut Foundation (TACF), where we grow several dozen chestnut varieties bred by the TACF and collect the seeds for analysis. TACF is experimentally growing and evaluating different strains of hybrid American and Chinese Chestnuts. The goal is to breed a tree that retains the Chinese chestnut’s resistance to the blight, but also has the form and leaf palatability of the American chestnut. The leaves of Chinese chestnut trees are thick and hairy, which tends to reduce their palatability to herbivores. Hand pollination is employed in experimental groves to selectively cross particular trees. The chestnuts produced from hand pollination are harvested, planted, and assessed for resistance and other traits. As of 2018, there were 900 trees in our plot, which has a fence to keep out deer. In addition, TACF utilizes transgenic technology, inserting a wheat gene that encodes an OxO enzyme (oxilate oxidase), which degrades the oxalic acid toxin that makes chestnut blight lethal. Our long-term hope at Mt. Cuba is to be able to plant resistant chestnut trees throughout our landscape where they can once again serve the ecosystem.
Other plant diseases that were introduced to North America and caused a decline in native tree populations include Dutch elm disease, which decimated the American elm, and butternut canker, which has diminished populations of white walnut (also called butternut) in several states and in Canada.
Protecting Plants in Your Garden
Here at Mt. Cuba Center, we monitor our plants closely for signs of disease, but we also minimize stress to new plantings. Plants are more likely to be affected by disease when they are under stress, which can result from a variety of factors, including rainfall, humidity, fungus, bacteria, and/or insect damage. Human or mechanical factors–such as improper planting, chemical use, habitat disturbance, and fragmentation–can also cause stress to a plant. You can minimize stress to your plants by selecting species that have evolved to thrive in your soil, sun, and moisture conditions. It’s recommended to plant in spring or fall when temperatures are not very hot, and water plants while they get established.