Genetically Modified Trees: A Case Study on the American chestnut.
Part I: A Walk in the Woods
The summer before Mary’s first semester in college she, her father Jethro, andher sister Ruth were deep in to their weeklong backpacking trip through the Big Ivy area of Pisgah National Forest in western North Carolina’s Black Mountains. By now their bodies felt broken in to the rhythmof trail life—dark night skies, soft night sounds, the steady beat of feet on the trail, and the weight of a pack on the back. The trail threaded its way through Appalachian mixed hardwood forests dipping down into cool shady areas dominated by mountain laurel, then up into higher and dryer ridges dominated by oak and hickory trees. Occasionally, the trail would move through cooler and wetter areas growingstriped maple and Frasier magnolia.
Ruth and Mary, ever the keen observers, noticed a pattern in the landscape—in areas where the soil was rocky and thin an occasional stumpstood, in an advanced state of decay, with a small tree shooting up out of it. During a brief rest to enjoy a sip of water Ruth asked Jethro “What are these trees called dad? I keep noticing them in the understory but I have yet to see one larger than a dogwood. They have these fruits with a spikeyhull. Here, see?” Jethro and Mary examined the spiny fruit and Mary said “I wonder what is inside the hull? Let’s see.” Using her pocket knife Mary pried open the spiny green hull. Then she dropped thehulls to the ground and what remained were three fuzzy, shiny nuts. “Are these edible?” askedMary. “They may be.”said Jethro. “I wonder why these trees only appear to grow out of these nearly-gone stumps?” asked Mary, as she squatted to get a closer look at one. Jethro replied “Sounds like we’ve got lots of questions to answer girls.
And I think I know just the man who has the answers we want.”
1.What answers do you have? Generate three hypotheses to the questions Ruth and Mary asked above. Why are the trees growing out of stumps?
Part II: A Dance at the Barn
A week after their backpacking trip Mary and Ruth were well-rested and gearing up for an evening playingmountain music at the barn dance. The girls thoroughly enjoyed playingtraditional Appalachian, Celtic, bluegrass, and old time tunes with the Flat Creek Boys. Mary especially enjoyed these times playing music with the Boys. She made a point to treasure each tune. Soon, she thought to herself, I’ll be heading off to college to study forestry. I won’t see these folks for some time. I want to enjoy every minute.
Mary’s fiddle playing and Ruth’s mandolin playing were a welcome accompaniment to the upright bass, guitar, and banjo the Flat Creek Boys played. One of the Flat Creek band members, Abe, could really carry a tune on the five-string. Abe had been playing the banjo since he was nine years old, and now he was ninety-nine. After a night of foot stompin’ and fiddle tunes Mary, Ruth, and the Boys all settled down inrocking chairs to relax. Jethro and his wife Jael joined the girls to visit a while. “Mary, Ruth, do you remember how I said I knew just the man to ask our tree questions to?” said Jethro. “Well, Abe here knows these mountain forests better than anyonerocking on this porch. Abe, have you ever seen one of these?” Asked Jethro. “Why sure.” said Abe. “That’s a chestnut. My granddaddy used to pick those up by the bucket-full. He’d feed em’ to the hogs, roast some on the fire for us to eat. He’d even sell some at the market. Many a time those chestnuts would get us through the hungry-gap in spring—the time when the larder was getting low and there were no crops yet to gather in.” Said Abe.
“Your granddad used to gather those by the bucket full? Those trees must have been huge! Why are they all so small now? I remember the Browns have a chestnut tree at their farm and it is far bigger than the ones we’ve seen here in these woods.” said Ruth. “The only ones we saw inthe woods now are small, and they don’t bear many nuts.” said Jethro. “The blights what happened.” Said Abe. “The ‘blight’? “What do you mean?” Asked Jethro. “Yeah. What is the chestnut blight?” asked Mary. “A blight come from up north and swept down through the forests and took out all the chestnuts.” Said Abe. “By the time I was old enough to work the sawmill we were cuttin’ down the chestnuts and makin’ a good deal of money on the market for the lumber. Chestnut wood went for a premium price. They was all dyin’ off. Hated to see it but we were tryin’ to make a living. Of course none of the trees grew back. The sanctuary of the Presbyterian Church here in the cove is paneled with chestnut. Beautiful wood.” Said Abe.
Later that night, back home, Mary thought to herself A blight swept down through these forests and wiped out the chestnut trees. Where did it come from? What exactly is a “blight”? It must have killed off the trees quickly, I wonder how long it took? How come some of the trees are still alive today but they don’t grow any bigger?Is the chestnut tree at our friend’s farm the same kind of chestnut as the one’s we saw in the woods?Mary’s questions faded into the recesses of her consciousness and stayed there for quite some time. With all the activities necessary to prepare for her move to college the chestnut questions had to stay in the back of her mind until another day.
1.Hypothesize: generate a hypothesis in reply to Mary’s questions. You do not have the full picture yet, but what do you predict you will find? What exactly is a blight? Where do you think the blight that killed off the chestnut trees in eastern North America came from? Why are some chestnuts still alive today? And why are they not as big as they once were decades ago?
Part III: College Work
Now that the first month or so of the fall semester was behind her Mary finally felt like she was settling in to a groove. Mary was enjoying the comradery of a community of peers all devoted to learning. She particularly enjoyed her general biology and introductory forestry courses. She was feeling a little anxious though, as she had to settle on a final research project for her biology course. Just yesterday her biology professor encouraged her students to begin their research with a question. “What are you curious about?” The professor asked. Mary thought for a moment. Then she remembered: chestnuts. She was determined to resolve the questions she had about the chestnut blight.
TedX TalkESF/SUNY video Biology of Cryphonectria parasiticaThe American Chestnut Foundation’s Science Strategies Additional TedX Talk referring to hypovirulence
Additional Technical Resources:
Genomic Selection for Blight Resistance Hypovirulence
1.Help Mary with her research project. Access the resources linked here. Sort the information regarding the origin and spread of the blight into a simple timeline.
2.Furthermore, illustrate the lifecycle of the blight.Draw a cyclical illustration of the blight infecting a chestnut. Begin with infection, cycle the illustration through the entire lifecycle of the blight as it impacts a chestnut tree, damages the tree, and re-infects other trees.
3.Now that you have illustrated the lifecycle of the chestnut blight and sketched a rudimentary timeline of the origin and spread of the blight in eastern North America, what kind of organism is the chestnut blight? Review your biology textbook andthe resources accessed in question one, above. Is the blight an animal? A plant?Fungi?Bacteria? Virus? Protist?
4.How did the blight get started? Where is it originally from and where did it spread outward from in the US?
Part IV: More College Work
Mary was relieved to finally get some answers to her questions. However, she felt saddened by the demise of the American chestnut. It was such a beautiful tree that had provided a reliable source of food for people and wildlife for thousands of generations. Then the tree was gone from the forest in about forty years! During Mary’s initial research she read that scientists were working on restoring the American chestnut to the woodlands of eastern North America. Intrigued, Mary decidedto learn more.
1.Why do scientists want to bring back Castanea dentata(American chestnut) tree? List eight reasons.
2.What is the difference between Castanea dentata and other species of chestnut? What is the natural geographical native range of Castanea dentata? What is the geographical range of Castanea mollissima?
3.What are scientists doing to bring back the American chestnut tree? Pick one strategy scientists are employing and describe the technologies in detail.
4.Explain and describe the use of Agrobacterium tumefaciensto transform plants like the chestnut.
5.Describe the work scientists are conducting at SUNY on American chestnut trees. How do the American chestnut trees SUNY scientists develop resist the blight? Why is it important for scientists to increase genetic diversity of the modified trees before implementing them into a landscape-scale restoration project?
6.How are SUNY’s efforts towards restoring the American chestnut different from what TACF is doing at their Virginia-based orchard?
7.Describe the effectiveness of hypovirulence.
8.Explain the process of backcrossing that TACF and scientists like H. Craddock use.
Part V: Management Plans and Plans to Manage
Now that Mary had thoroughly researched the origin, spread, biology, and restoration-science of the American chestnut she felt a fire insider her. She sensed an internal pressure and drive to continue learning. She wanted to join the work of the scientific communities she’d readabout in restoring the American chestnut to its natural range. Over a meal with some friends at a local diner Mary shared her aspirations. One of her friends replied “So scientists want to plant genetically modified trees in our forests? I am not so sure that is a good idea.” Mary thought for a moment, then replied “Yes, but the trees are safe. And they provide a reliable source of food for wildlife and people.” Her friend replied “I have serious reservations about GMOs. Wouldn’t the GMO chestnut trees harm wildlife and people?”
1.Join the conversation. Review the information in the following resources: Interactions withTransgenic American Chestnutsand Biotechnology for Forest Health?
2.What negative interactions between transgenic chestnuts and other organisms have scientists observed and documented?
3.Describe and explainat leasttwo concerns individuals and organizations hold regarding the introduction of transgenic American chestnuts to forest ecosystems.
4.Are you aware of other efforts to reintroduce a species to a large geographical area that have also stirred up controversy? See if you can identify one case in recent history, not including the efforts to reintroduce the American chestnut.
5.Where do you land? Are you in favor of restoring the American chestnut population of eastern North America with the transgenic chestnuts currently under research?