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3 Unusual Ideas to Cure Elm Yellows (Elm Phloem Necrosis)

Elm trees have not had a good century. Dutch Elm Disease, caused by fungus and spread by a beetle was introduced into the United States from Europe in the 1920’s. Since then we have created fungicide sprays and cultivates of Elm trees that are resistant to Dutch Elm Disease. Just when we thought it was all good. Elm Phloem Necrosis has spread and developed as a new threat. This disease will wipe out the remaining adult Elm trees in North America. What is Elm Phloem Necrosis?

Elm Phloem Necrosis is a disease caused by phytoplasmas, which are parasitic bacteria that do not have a cell wall. They are so specialized to live within a plant that they can not survive on their own. This makes them very difficult to culture and study. While the disease is caused by phytoplasmas it is spread by leafhoppers.

A Leafhopper on a leaf. Leafhoppers are insects that are common pests to plants. Leafhoppers can also spread elm phloem necrosis.

Idea #1 Hybrids and Genetic Modification

The reason why hybrids are typically better than their parents is because of genetic diversity. When Dutch Elm Disease was discovered many of the Elm species were screened for resistance. None was found. Cultivars have been developed to be less susceptible to Dutch Elm Disease and Elm Phloem Necrosis. However, no known species of Elm is completely resistant to these two diseases. So we either screen again for resistance from the Elm species that were not tested for resistance or we use genetic information from something more different than Elm. Ulmaceae, the family that Elm trees belong to has other genuses. Including Ampelocera from South America and Zelkova from Southern Europe and Asia. Two species might provide this diversity: Zelkova serrata from Southeast Asia and Ampelocera hottlei from Central Mexico. Zelkova serrata has shown to be highly resistant to Dutch Elm Disease but is still susceptible to Elm Phloem Necrosis (Missouri Botanical Garden).

How would we create a Hybrid between species from two different genus? That would be like making a hybrid with your cat and a lion. There are a few ways. We could fuse cells from the two different species together. Or extract the DNA from one species, break it up into big pieces, make lots of copies, then coat gold nanoparticles with the DNA then shoot it into the other species. Or combine the sperm of one species and the egg of another then double the chromosomes to get a viable hybrid. I list these options to show that it is possible to do with today’s technology. The problem with this solution is that it is slow and takes time. Even if the hybrid created was completely resistant to diseases it would still take time for it to grow into an adult tree. What is a quicker solution to kill the bacteria that causes Elm Phloem Necrosis?

One of the quickest ways to kill bacteria was discovered over 1o0 years ago, electricity. When electricity was able to be produced regularly people started experimenting with it and one thing they tested was killing bacteria and microbes. You might be thinking right now of that fishing joke that the lazy fisherman throws a bug zapper into a river and all the fish die from electricity. Oh, well I’m thinking of that joke. In practice, it would be the same thing. Electricity can kill both bacteria and fish. We use electricity to punch holes in a bacterial membrane to put DNA inside the bacteria. Elm Phloem Necrosis would be a good disease to try this because the bacteria only has a membrane and not a cell wall, making more susceptible to this technique. How would we try this? Attach one electrode to the roots and one to the stem and plug it into a socket? The problem is that the amount of electricity needed for a whole tree would be enormous. It might be possible to attach a copper wire to the tree and shoot up a rocket causing lighting to hit the tree. That might work. Another way would be to go small. The smaller you are working with the less electricity needed to kill the bacteria. If the electricity is applied directly to the bacteria then this method would be feasible. How could we do this? A membrane inserted into the tree that gives a shock to bacteria in the phloem.

 

A membrane diagram to kill elm phloem necrosis or bacteria in a tree or suspended liquid. The bacteria flows through and next to two parallel lines, which show the membrane. Sensors are on the lines. When the sensors detect the bacteria electricity is released killing the bacteria. Water and sugar is free to flow through the membrane.

 

Bacteria would flow through the membrane. A sensor would detect the bacteria and release a shock. Water and sugar could move freely past the membrane. The problem with this solution is that the technology needs to make this membrane does not exist. At least not that I am aware of.

What would be a way to kill the bacteria in the Elm trees that already exist? Antibiotics such as Tetracyclines have already shown to slow Elm Phloem Necrosis. We already kill bacteria in a different way to prevent our socks from getting smelly. We use silver nanoparticles to kill odor causing bacteria. We could inject the tree with silver nanoparticles or put the particles into the soil where they would be absorbed by the roots. This could be a way to cure Elm Phloem Necrosis. There are a number of unknowns with this approach. It would work in Elm trees since we do not eat Elm trees, however, what would happen if a pest like a leafhopper ingests some silver and it is transported to a crop that we do eat? What would be the effect on human health?

Elm Phloem Necrosis could wipe out the remaining Elm trees in North America. It is caused by a phytoplasma, which is a primitive bacteria without a cell wall. One way the disease is spread is by leafhoppers. I proposed three possible solutions for Elm Phloem Necrosis: hybrids, electricity, and silver nanoparticles. Each has a strength and a setback. Let’s find a solution to this disease before Elm trees are gone.

Sources:

Missouri Botanical Garden. Zelkova serrata. http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a927

Elliott Killian

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