进军森林
A GM species may soon be liberated deliberately
一种转基因树木不久或将大量种植，但很审慎
May 4th 2013 | From the print edition
The way they were
最初的模样
ONCE upon a time, according to folklore, a squirrel could travel through America’s chestnut forests from Maine to Florida without ever touching the ground. The chestnut population of North America was reckoned then to have been about 4 billion trees. No longer. Axes and chainsaws must take a share of the blame. But the principal culprit is Cryphonectria parasitica, the fungus that causes chestnut blight. In the late 19th century, some infected saplings from Asia brought C. parasitica to North America. By 1950 the chestnut was little more than a memory in most parts of the continent.
民间流传有这样的故事：很久很久以前，松鼠在穿过美国缅因州到福罗里达州的栗树林时，可以一直不触碰地面。估计北美那时的栗树约有40亿棵。现在却不复存在了。必须说，斧头锯子不乏其罪，但栗疫病菌[sup]【1】[/sup]才是罪魁祸首，是这种真菌致栗树感染了栗疫病[sup]【2】[/sup] 。19世纪后期，一批亚洲来的感染栗疫病菌的树苗把该病菌带到了北美。到了20世纪50年代，北美大陆大部分地区的栗树便全部消失，成为了回忆。
American chestnuts may, however, be about to rise again—thanks to genetic engineering. This month three experimental patches will be planted, under the watchful eye of the Department of Agriculture, in Georgia, New York and Virginia. Along with their normal complements of genes, these trees have been fitted with a handful of others that researchers hope will protect them from the fungus.
但有了基因工程，美国栗树有望再次繁茂起来。在美国农业部的密切看护下，将于本月在乔治亚州、纽约州和弗吉尼亚州分别栽种一片栗树林进行实验。这些栗树除携带正常的附加基因外，还添加了少数不同寻常的附加基因。研究者希望通过添加这些基因来防止栗树被真菌感染。
The project has been organised by the Forest Health Initiative (FHI), a quango set up to look into the idea of using genetic engineering to rescue species of tree whose populations have been devastated by fungal diseases or insect pests. It has sponsored research at several universities, and this month’s trial is the first big field test. If it works, the FHI will ask the government for permission to plant transgenic chestnuts in the wild, with the intention of re-establishing the species in America’s woodlands. And if that goes well, it could provide a model for projects to re-establish elm trees (being devastated by Dutch elm disease, a beetle-born fungal infection), ash trees (threatened in North America by a beetle called the emerald ash borer, and in Europe by a fungal disease called ash dieback) and a fir tree known, confusingly, as the eastern hemlock (which is plagued by the woolly adelgid, a sap-sucking bug).
该项目的组织者是一个半官方机构——森林健康行动（FHI），该机构的创立是为了检查用基因工程来拯救被真菌病或害虫摧毁的树木种群的可行性。FHI已在几所大学发起了研究倡议，并于本月迈出大型实地试验的第一步。如果可行，FHI则会向政府申请在自然环境中种植基因改良栗树，以重建美国林地的栗树林。如果这也可行，那就能为榆树（被荷兰榆树病[sup]【3】[/sup]——一种由甲虫传播的真菌感染摧毁）、白蜡树（在北美的受到吉丁虫[sup]【4】[/sup]的威胁，在欧洲的受到顶梢枯死[sup]【5】[/sup]真菌病的威胁）和杉树（名称有点混淆，亦名加拿大铁杉，患了由球形蚜——一种刺吸小虫引起的虫瘟）重建项目提供示范。
The search for genetic protection for the chestnut was begun in 1990 by William Powell of the State University of New York, in Syracuse, and Scott Merkle of the University of Georgia, in Athens. Dr Powell knew that many of the symptoms of chestnut blight are caused by the oxalic acid that C. parasitica generates as it grows. He also knew that wheat has an enzyme called oxalate oxidase, which detoxifies oxalic acid. He and his team therefore transferred the gene that encodes oxalate oxidase from wheat to chestnut. Last summer they showed that oxalate oxidase can indeed enhance blight-resistance.
栗树基因保护研究始于1990年，由锡拉丘兹市纽约州立大学的威廉•鲍威尔和爱森斯市乔治亚大学的斯科特•默克尔共同进行。鲍威尔确信，栗疫病的很多症状都由栗疫病菌生长时产生的草酸引起。他也清楚，小麦有一种草酸氧化酶，能够分解草酸。于是，鲍威尔和他的团队将小麦中能够编码草酸氧化酶的基因转移到了栗树的基因中。去年夏天，他们证明了，草酸氧化酶的确能够增强栗树的抗枯萎性。
A few years ago the Forest Health Initiative asked Dr Powell and some other researchers doing related studies to look at the work of the American Chestnut Foundation, a group which had been crossbreeding Chinese and American chestnuts. Since C. parasitica is Asian, Asiatic trees have evolved resistance to it. The foundation hoped to make a hybrid sufficiently Chinese to be protected, but sufficiently American to pass muster as local.
几年前，FHI邀请了正在进行相关研究的鲍威尔博士和另一些研究者研究美国栗树研究基金会（该小组已成功将板栗和美洲栗杂交）的工作。由于栗疫病菌发于亚洲，亚洲树种已经形成了对该真菌的抗性。
With the aid of the genomes of the two species, Dr Powell and his collaborators began testing 27 Chinese chestnut genes in the American tree. The 800 trees to be planted this month will contain various combinations of these genes, the original wheat gene and six further genes from other tree species. And results should come quickly. Field tests for blight-resistance are typically done when trees are a few years old, but Dr Powell’s team have devised a test of the sapling’s leaves that they believe can tell whether a tree is resistant when it is less than a year old.
借助两种栗树的基因组，鲍威尔博士及其合作伙伴开始在美国生长的树上测试27种板栗基因。本月将栽种800棵树，这些树包含了原小麦基因以及其他树种6种基因的各种组合基因。预计结果很快就可以得出。抗枯萎性的实地试验一般要当树木生长几年之后才能进行，但鲍威尔博士研究小组想出了一个测试树苗叶子的办法，他们认为可以在树龄不满一年的情况下测试出树的抗性。
The trial itself will last three years, and the researchers running it will monitor how the modified chestnuts fit in to the local ecosystem, as well as how healthy they are. If they both do fit and are fit, a decision will then have to be made about whether to release them into the wild. That will be up to the Department of Agriculture, the Environmental Protection Agency and the Food and Drug Administration.
这项试验会进行三年，进行该试验的研究者将持续观察记录改良过的栗树在当地生态系统的适应程度以及它们的健康状况。如果能够适应并且长势良好，那是否要在自然环境中大量种植就得由农业部、环境保护署和食品药品监督管理局来决定了。
Until now, the genetic modification of trees has had strictly commercial aims: speeding up the growth and extending the environmental tolerance of species intended for plantations. This use of genetic modification has been opposed by environmentalists, who fear that such “supertrees” may escape and damage wild forests. The Forest Health Initiative’s goal, though, is to heal wild forests, not hurt them. If its experiments do produce a strain of chestnut that could do the job, it will be interesting to see how enthusiastically greens embrace it.
迄今为止，改良树木基因带有明确的商业目的：一是催长，二是为了造林增加物种对环境的容忍度。为达到该商业目的使用转基因，遭到了环保主义者的反对，他们担心这样的“超级树”会疯长进而危害到野生丛林。但FHI的目标是为了恢复而不是危害野生丛林。如果试验成功，真能培育出抗栗疫病菌的新品种，那看看“环保党”在欣然接受时会表现出怎样的欢欣鼓舞，还挺有意思的。
From the print edition: Science and technology
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译者注：
【1】栗疫病菌：Cryphonectria parasitic。主要为害主干及主枝，少数在枝梢上引起枝枯。初发病时，树皮上出现褐色水浸状稍隆起的病斑，内部组织湿腐有酒槽味，发病中后期病斑失水凹陷，在树皮下产生黑色瘤状小粒―病菌子座。以后子座顶端破皮而出，在雨后或潮湿条件下子座内溢出黄色卷须状分生孢子角。最后病皮干缩开裂，在病斑周围产生愈伤组织。
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