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American Forest Before the Chestnut Blight
Once upon a time, American deciduous forests were filled with a magnificent tree, the American chestnut tree. It is estimated that, prior to the twentieth century, a quarter of the trees in the forests of Appalachia were chestnut trees. The trees grew to 30 metres (98 ft) in height and were prized for giving stout timber and large quantities of delicious nuts. They were also renowned for their beauty. But then, something bad happened. In 1904, some Asian chestnut trees were planted in the Bronx (in what is now the Bronx zoo). These Chinese chestnut trees had a pathogenic fungus, Cryphonectria parasitica, living on them. Chestnut tree species of Asia have evolved some defenses to this rapidly spreading fungus, but the two American species were completely unprepared. By 1950, the blight had killed more than four billion trees and only strange isolated single specimens and sad still-living (yet undead) stumps remained. The chestnut blight opened our eyes to the perils of invasive species in a world of almost-instant shipping (although I don’t think we have yet fully understand how pervasive and potentially dangerous fungi can be), it also marked an irreversible change to our beautiful forests…
Evidence of the Chestnut Blight!
Except maybe not. Molecular biologists, mycologists, and arborists have been quietly working for years to hybridize a blight-resistant modern American chestnut tree. They failed at hybridizing a vigorous tree with the desired characteristics of the original American chestnut trees, so they turned to transgenic tinkering and this technology has yielded results. The American Chestnut Research and Restoration Project at New York state’s College of Environmental Science and Forestry has utilized the same sort of technology behind genetically modified crops (like BT rapeseed and such) in order to create American chestnut trees which have a gene from wheat that helps the trees survive and tolerate Cryphonectria parasitica. The American Chestnut Research and Restoration Project is readying an army of these genetically altered trees to go into the wild forests and reseed North America as it used to be, but their plan is not without controversy.
Some opponents worry (understandably) that bringing back the chestnut will represent “a massive and irreversible experiment” on our living forests. Additionally, as we know from the hysterical response to transgenic crops in Europe and even here, many people are extremely emotional and ill-informed about gene-manipulation technologies (probably because the phrase “gene-manipulation technologies” sounds so much like a 1950s horror movie tagline). Transgenic blight-resistant American chestnut trees still need regulatory review from the Food and Drug Administration (and maybe the Environmental Protection Agency) before they can be planted and allowed to disperse pollen. Such a process may take many years. Yet tree lovers and concerned ecologists point out that the near-extinction level mass deaths of American chestnuts was caused by humankind’s actions and choices. And more blights are arriving every year to destroy other cherished species of trees. We live in a world of emerald ash borers, Dutch Elm Disease, spotted lantern flies, gypsy tent moths, and oak wilt. If we don’t start doing something, the only tree left might be the diabolical invasive tree of heaven (I can’t believe nobody commented on that post! Am I the only person to despise that nightmarish monster?).
The regulators are starting to analyze the proper course of action, and I guess we will be hearing more from them, but, in the meantime, what do you think?
Remember when I wrote about Panama disease, the fungal blight which is coming for the Cavendish bananas (after laying waste to the Gros Michel cultivar bananas back in the 50s)? Well, sadly, Panama disease is not the only apocalyptic fruit blight on the international circuit these days. It turns out that a bacterial disease is destroying citrus groves around the United States and beyond. The disease, known in English as “citrus wasting disease” is caused by a motile bacteria, Candidatus Liberibacter, which is spread by the Asian citrus psyllid (Diaphorina citri), an inconsequential Hemipteran insect which lives in citrus groves. There are multiple strains of greening disease, and there have been for a long time, but the newly problematic strain originated in China where it is known by the evocative name “huánglóngbìng” which means “Yellow Dragon Disease.”
A revolting Asian citrus psyllid, Diaphorina citri
The wild ancestors of most of today’s grape fruits, oranges, and lemons, came originally from the forests of East and South East Asia so it is not a huge surprise that this horrible disease comes from there too. Unfortunately hemipteran insects can easily proliferate in new ecosystems, so the disease became a problem after these invasive insect pests gained a widespread foothold throughout the semi-tropical regions where citrus is grown.
A tree infected with citrus greening disease
Citrus fruit is delicious and wonderful beyond compare…so it is worth big money. This means that agricultural scientists have been studying huánglóngbìng and attempting to stymy it with medicines, pesticides, and transgenic tinkering. The scientists themselves have been hampered in their research by the fact that it is hard to maintain and study citrus plants infected with the disease because they die so swiftly (the infected citrus plants, not the agricultural scientists). Powerful antibiotics work to wipe out the disease, but it is not practical to give these medicines to trees (though we will probably try—with predictable results). Scientists feel that there may be a transgenic solution, but it is unclear how marketable such a chimera will be (since protectionists and Luddites have been fear-mongering pretty hard against GMOs).
This leaves mass application of insecticide as the best bulwark against huánglóngbìng. It is starting to seem that small orchards and groves which are unwilling to commit to this kind of regimen will soon be gone. All of this strikes me as unbearably sad and frightening. Why are there so many blights everywhere? Has this always been a peril of agriculture (indeed of life?) or has contemporary monoculture paved the way for widespread proliferation of these superbugs? There must be some parasitoid wasp or something which has kept these damn psyllids from wiping out species citruses of wild Asia. Maybe we could bring that here…but it probably would cause some new horrible problem.
We’ll keep you posted. In the meantime you should glut yourself on oranges this winter…while you still can.
Australian Banana Groves Destroyed by Panama Wilt
Sooo…I try to keep it light on Mondays so we can get through these long weeks, but one of our recent posts demands an immediate follow-up. Remember how I was discussing the grim fate of ‘Gros Michel’ (‘Fat Michel’) the strain of bananas which were wiped out by Panama disease in the 50s? Well, Panama disease has mutated and returned. It’s baaaack…and this time it destroying the once immune ‘Cavendish’ plants which make up almost every banana in Europe, Africa, and the New World Photos are becoming more and more common of dying banana plants and desperate farmers burning their groves. ‘Cavendish’ plants are clones and if one is susceptible, they all are. I really like bananas (when they are ripe) and the idea of doing without the radioactive potassium-rich fruit makes me sad. What are we going to do?
We have the technology?
I guess a good market solution would be to make a transgenic banana that was resistant to the Panama disease, patent the critical gene fragment, and then sell sterile clones of the frankenfruit. Since I like science and bananas (though not necessarily giant agribusinesses) so this is an acceptable solution to keep the yellow fruit on the table.
Industrial banana washing in Costa Rica
An alternate idea, however strikes me as far better. We should send out teams of banana farmers and taste-testers to South East Asia (the first home of the banana) to collect purple, white, red, and gray bananas. Different folks can start growing all sorts of new bananas around the world. Undoubtedly some of them are more delicious than ‘Gros Michel” and I bet they are all more resistant to the blight.
In fact just yesterday, regular Ferrebeekeeper commenter Beatrix reported on the delicious (albeit plain-looking) bananas of Nepal. She writes:
Here in Nepal we have all sorts of different bananas growing wild & in cultivation. They vary from short sweeties to starchy plantain sorts. Nepalis don’t have names for the different types of bananas. One of the tastiest varieties here is the ugliest – it is rather small (fingerlike), sporting a mottled greenish black peel with patches of gray lichen when ripe. The peel is surprisingly paper thin but the the flesh is a rich golden yellow & the taste is the most incredible, sweet custard-y banana flavor ever. I have never tasted this type of banana anywhere but Nepal. Most Asians prefer the starchy, bland bananas that most westerners would consider unripe – they think by the time a banana gets to the yellow mottled with brown stage it’s rotten.
Who here doesn’t want to try these delicious ugly bananas? I am ready to pack up and head off to Nepal just to try them! What we have is a marketing problem. If these charlatans can sell people on stuff like organic food and bottled water, why can’t they sell delicious (but ugly) finger-length bananas? The second coming of Panama disease needn’t spell the end of bananas (although we may lose the familiar bright yellow “Cavendish”)—perhaps this could be the beginning of a glorious new era of multicolor bananas of all sizes and flavors!
Or we could use technology and modern farm techniques to make some crazy bananas!
Gros Michel Bananas
A half a century ago, bananas were more delicious. They were creamier with a more delectable tropical fruit taste. When they ripened, they stayed ripe longer instead of swiftly turning to black slime. Since they lasted on the shelf when ripe it was possible to sell them ripe–as opposed to today’s bananas which must be purchased all green and hard and nasty. I realize that this description makes it sound like I have fallen prey to golden age syndrome—wherein a bygone time becomes a misremembered quasi-mythical standard against which today is unfavorably compared (a well-known problem for certain political parties and demographics)—yet I am not embellishing. The bananas of yore were better because they were different. If you recall the earlier banana post, you will remember that there are numerous strange and magnificent varieties of bananas in Southeast Asia—delicious miniature bananas, red bananas, purple bananas…all sorts of fruit unknown to us. For long ages, across many lives of men, farmers hybridized wild species of bananas and selectively bred the different strains into different varieties called cultivars. The most delicious and salable cultivar was “Gros Michel” (Fat Michael) which I described above. “Gros Michel” was so ideal for farming (and so tasty) that it became pretty much the only banana cultivated. Vast plantations around the world produced only “Gros Michel.” It grew on large 7 meter tall trees (21 feet) which produced abundantly.
I even have a family story of how my paternal grandparents got together during World War II. He finally expressed his interest in her by giving her a banana—which were rare and precious during the war. Grandma was suitably impressed and made a somewhat ribald poetic metaphor concerning the banana’s shape–which left grandpa with no doubts about her feelings…which is to say I am considerably in debt to “Gros Michel”, despite the fact that I have never tasted one.
So what happened to Gros Michel? Is there by chance a terrifying horror story which provides us with a useful moral lesson about our tastes, our habits, and the fragile nature of the foundations of civilization?
Well, as it happens there is such a story!
Banana Tree with Panama Disease
In the 1950s, a fungus Fusarium oxysporum attacked the Gros Michel bananas. It was known as “Panama Disease” and it wiped out entire plantations of fruit in Africa and South America. The blight spread with horrible speed through the great monoculture farms. All Gros Michel bananas were clones, so the contagion spread unchecked. There were years where there were almost no bananas in Europe, Africa, and the Americas: whole empires turned to ashes and rot. To save their livelihood banana growers burned their groves and moved to a new dwarf banana “the Cavendish” which was unsatisfying—but which resisted the terrible killing fungus. Gros Michel disappeared from the commercial world…although there are tantalizing rumors that it exists still in the ancestral homeland of bananas—Southeast Asia. It has even been said that Chinese billionaires import luxurious Gros Michel fruits and have lavish banana parties where they eat magnificent tasting bananas and laugh at the feeble little green bananas of the west.
Whatever the truth of these tales, what is certain is that the banana growers outside of Asia immediately fell back into their bad habit of monoculture. The Cavendish is just as vulnerable to blight as its predecessor. Indeed many monoculture crops (crops like wheat, rice, and potatoes) are potentially vulnerable to unexpected disease because of the perils of overreliance on certain favorable strains. It is a somewhat sobering thought for people who eat!
My garden in Brooklyn at the end of June.
My summer garden looks a lot different this year for two reasons. First of all, the hydrangea finally started blooming! It has magnificent human head-sized blossoms the color of blueberry ice cream (or maybe I should say the color an alien gas-giant planet) and I love it. I thought the poor thing was dead for a year and a half but now it is the centerpiece of the garden! There is an allegory about hope in there somewhere.
The second big change is more disquieting. In shade gardens, the best way to get a colorful ground cover is to plant impatiens—tiny jewel-like five petal flowers which easily grow into a dazzling multicolor carpet. Because they are cheap and hardy (and beautiful–despite what flower-snobs say), I usually carpet my beds with them. But this year things went very, very wrong for impatiens. A deadly strain of downy mildew has struck down happy little impatiens across the nation and beyond. The pernicious fungus is named (Plasmopara obducens) and it has spread like an Old Testament plague through the United States and Great Britain (as painfully detailed in this excessively wordy NY Times article). I bought a few flats of impatiens from the hardware store at the beginning of spring—but after that there were no more. I fret that the little red and pink flowers could fall dead at any moment.
Vinca “Jams ‘N Jellies Blackberry” (that doesn’t get easier to write)
To make up for all of the coral and purple impatiens which I never got a chance to obtain, I bought a bright white New Guinea impatien (which you can’t see in the photo up there) and it is magnificent, however it was so expensive that I only bought one. I filled up the remaining beds with weird purple-black vincas agonizingly named “jams ‘n jellies blackberry” (who comes up with these names? Maybe the seed companies should hire some of my poet roommates). The vincas are growing very slowly. It is unclear if they will be able to set roots and flourish before the evil squirrels dig them all up.
New guinea impatiens are so pretty!
So my garden is all ferns, Persian shields, caladiums, vincas, and lilies. I am hopelessly drifting back towards Victorian England while the rest of the world is going all ahead towards ultra- cyber-hip-hop (which is represented in the garden by what exactly? picotee morning glories, track lighting, and giant aluminum cylinders maybe?). Anyway I also planted some weird autumn plants—passionflower vines and toad lilies—so check back in late summer to see how those turn out!
Treaty of Penn with Indians (Benjamin West, 1772, oil on canvas) shows Penn treating with the Delaware under under the great elm at Shackamaxon
Elm trees (genus Ulmus, family Ulmaceae) are deciduous and semi-deciduous trees which come in all sorts of shapes and sizes. They first evolved 40 million years ago in central Asia, and since then they have spread around the entire northern hemisphere, even crossing the equator in the rain forests of Indonesia–and that is just the natural distribution of these trees. During the eighteenth and nineteenth century elm-loving gardeners took the plants elsewhere on the globe, particularly Australia, which is now renowned for its avenues of elms. But the pinnacle of elms was in America: the American elm is a particularly large and beautiful member of the family capable of growing 50 meters (130 feet) high and 40 meters (120 feet) wide in almost any soil. The American elm’s tapering curve caused avenues of the trees to look like gothic vaults. Many of North America’s streets used to be huge 100 foot tall glowing green cathedrals made of living elm.
Elm-lined streets before and after Dutch Elm disease
The use of the past tense has probably warned you that there is a horror movie twist to this story. Alas, in 1928, a shipment of logs from The Netherlands destined for use as veneer in the Ohio furniture industry arrived in America. The logs carried elm bark beetles which in turn carried ascomycete microfungi. It was the American beginning of Dutch elm disease, a blight which later wiped out millions of trees. Various different species of bark beetle are capable of transmitting closely related microfungi (namely Ophiostoma ulmi, Ophiostoma himal-ulmi, and the virulent Ophiostoma novo-ulmi). These fungi seem to be able to hybridize with one another and form new strains…with new strengths. The fungi apparently hail from China, but their province is unclear—at some point the trail goes cold (although Chinese species of elm seem resistant to the blight). Whatever the case, European and American elm trees were not ready for the spores. Even with heavy use of pesticide, fungicide, and aggressive quarantines, the great elm populations of Western Europe and North America dwindled to a fraction of what they were in the beginning of the twentieth century.
Life Cycle of Ophiostoma ulmi
Dutch elm disease is its own special horror if you are a lover of trees (which I imagine you are if you are reading this blog), but there is a darker terror lurking behind the blight. Dutch elm disease is one of the most famous blights of our era in North America so far, but it is by no means the only one. Merriam Webster defines a blight as “(a) a disease or injury of plants marked by the formation of lesions, withering, and death of parts; or (b) an organism (as an insect or a fungus) that causes blights.” These blights are spreading and multiplying. There is an oak blight, a bean blight, and a tomato blight. There are invasive tent caterpillars, mites, and galls. Although blights are technically defined as destroyers of plants, there are worrisome parallels in the world of animals. Frogs around the world have been dwindling from an exotic amphibian fungus. Bats in the northeast cannot hibernate thanks to a different fungus and they expire of energy loss. And the fungi are not the only worrying players. Everyone has followed the mass die-offs of honeybees from mites and who knows what else. The mixed-up super-fast dynamics of our human world mean that all sorts of critters, weeds, bugs, bacteria, protists, spores, and viruses end up traveling all over the place. How long till a Dutch elm disease type plague strikes some life form we hold even more dearly?
Before I creep anyone out too much by writing in this vein, it is instructive to look back at the fossil record of elms. This is not the first great die-back for the trees. According to pollen samples taken from ancient bogs, six thousand years ago, during the mid-Holocene period, all elm trees suddenly died back close to extinction in northwest Europe. To a lesser extent the same thing happened again 3000 years ago. It is possible that elm tree already establishing immunities to the current blights. As I mentioned before, most Asian species are at least somewhat resistant to the fungus, and certain individuals and cultivars of once-common European and American Elms are gradually being discovered. Our grandchildren might once again live on streets that are green cathedrals…
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