a Success

There is a lesson from this first dataset. Whenever new or suspect plant diseases arise we should immediately sequence transcriptomes from field collected diseased tissue. These days the cost of an RNAseq lane is reasonable and the assemblies are pretty decent. The data generated should rapidly provide valuable information about the nature of the pathogen and offer an initial insight into its genes. Whenever time is of the essence, transcriptome sequencing should be initiated as soon as possible.

We decided early on in this project that speed would be a critical driver given the emergency nature of the problem. We decided that we should generate genetic sequences as rapidly as possible, release them to the community, and prompt the crowdsourcing exercise we have been publicizing since Friday.


The seedlings that were placed into the ground came from generations of backcross breeding that date to the early 1980s. Matt Brinckman, the American Chestnut Foundation’s Mid-Atlantic Regional Science Coordinator, said the project began by crossing an American chestnut with a Chinese chestnut, which is resistant to the blight. The hybrids that were in turn resistant to the blight were crossed again with American chestnut — and again and again until scientists obtained a crossbreed that was 15/16 American chestnut and only 1/16 Chinese chestnut.

The American Chestnut Cooperators’ Foundation was co-founded by Gary Griffin, a plant pathologist at Virginia Tech. Instead of crossbreeding, that group has focused on finding the few remaining large American chestnut trees that have demonstrated partial blight resistance.

“We try to interbreed those to obtain greater levels of blight control,” Griffin said. “There aren’t many of these specimens, but we’ve found them and have been working with them for more than 30 years.”


We will rightly mourn the demise of ash trees from our woods, copses and country lanes if most of them succumb to deadly Chalara fungus. But the dead wood they will provide will be an enormous boost for Britain’s biodiversity. Dead wood is the richest habitat in a healthy forest. It supports a huge variety of wood-boring invertebrates, plus a battalion of fungi whose thread-like filaments penetrate deep inside to slowly decompose it, returning its nutrients to the forest soil.

A forest with plenty of dead timber provides a cornucopia of invertebrates for birds such as nuthatches, warblers and woodpeckers to feast on. And large dead trees, because rot holes more easily develop in them, are good places for hole-breeding species like bats, jackdaws and tawny owls.

If swathes of ash trees start dying Britain-wide, the policy of fell and burn to stop the spread of the fungus will serve no further purpose. Dead trees mustn’t be squandered.


There is no doubt that C. fraxinea’s introduction and spread has been due to the global plant trade. Millions of native tree and shrub species have been imported into Britain over the past 30 years, and planted in farm hedges, to replant woods and create new ones. Over a decade ago, members of the Horticultural Trades Association Tree Seed and Nursery Group and Flora locale were jointly lobbying for this to stop.

It has also become apparent that much of the ash imported was grown from British-collected seed, subsequently sent to the Netherlands for propagation, then returned as saplings to British nurseries. This aspect of the plant trade has clearly been instrumental in facilitating the spread of C. fraxinea. As a result of the import of this disease, nurseries are now facing huge costs associated with destroying their ash stock.

Fortunately, our native ash is genetically diverse and regenerates very easily from seed. Flora locale agrees with the Botanical Society of the British Isles, that its genetic diversity should protect wild populations. In Denmark, 90% of trees have been affected and in Britain, millions of trees will die, but disease-resistant trees will survive and regenerate naturally. This is another reason why it is madness to import what may be less genetically and maladapted ash (or indeed any other native species) ecotypes of Continental European origin. It would be equally mad to breed “disease-resistant” varieties and for these selectively-bred, genetically uniform, varieties to be widely introduced.

Research and practical projects (that Flora locale has showcased) have also demonstrated that tree seeding is just as effective as tree planting, with the added benefit that some natural selection will take place to weed out individual trees that are unfit to the planted environment. It has been a great disappointment that this approach has not been taken on board by government agencies and those major charities that undertake tree planting and woodland creation. Advice on methods using tree seed are available in Flora locale’s practice note on Creating Woodlands Naturally. 




If a disease like ash dieback affects a high proportion of the ash trees in a wild wood, it is unlikely that a casual observer would even notice. The rate at which resistant varieties of ash, or other species such as sycamore and cherry, would replace them would be much faster than the ten years or so that the disease is thought to take to kill a tree (in fact, ash dieback is not known to kill mature trees, so any sort of dramatic effect is very unlikely indeed).

The effect on ground flora and woodland animals is also likely to be negligible. Few species are dependent on ash for anything – mainly just other fungal diseases. If the proportion of ash in woodlands was to fall, the trees that would benefit, such as oak, may well have even higher ecological value (many hundreds of species are known to live on oaks).

Over the last 50 years the amount of ash, Fraxinus excelsior, in England and lowland parts of Wales and Scotland has increased greatly as a result of lower grazing pressure and the decline of elms.

Botanical Society of the British Isles – http://www.bsbi.org.uk/ash_dieback.html

An aerial photography company has created a map of all the trees in the country, which it says could prove vital in monitoring ash dieback disease.

Bluesky International, of Coalville, used photographic and infrared images taken from the air and combined them with height data to produce the 3D map of trees across England and Wales.

The firm said the map would be regularly updated so it could be used to monitor the effects of the disease which is threatening ash trees.

It is also planning to set up a web portal so experts can add the species of each tree to the map.


Conventional methods of testing for ash dieback rely on samples being sent to a laboratory from the outbreak site and it can take a number of days to get the results back. Using the Smartcycler, scientists and inspectors can take samples of potentially infected trees and test them for the presence of the fungus, getting the results back in just over an hour. The Smartcycler operates through a computer and is about the size of a large car battery, weighing about 10kg.


Ash dieback damage was assessed and analysed on 16–22 year-old grafts in two ash seed orchards (Fraxinus excelsior L.). The grafts originated from 106 plus-tree clones selected from 27 stands in southern Sweden based on their phenotypes. The results obtained indicate that ash dieback disease is strongly genotypically controlled. There was considerable genotypic variation among individuals. None of the clones seemed to be totally resistant, but some exhibited reduced susceptibility and retained this resistance after 6 years under heavy infection pressure.

Together with the high heritability of resistance, strong age×age correlations and weak genotype×environment interactions, this suggests there is good scope for breeding less susceptible trees for the future.


No ash trees in Bedfordshire have Chalaria fraxinea, the dieback disease sweeping the country.

A Department of the Environment spokeswoman said: “No incidences have been reported in the region at all.”


Skogforsk studies, though, show that traditional plant breeding has good potential for creating ash plants that are less susceptible to the disease.

In Nordic mythology, the Yggdrasil ash tree is regarded as the tree of life, but now the ash has been classified as ‘vulnerable’ on the Red List.

No clone is completely unaffected, but some are much more resistant than others. Consequently, traditional plant breeding seems to have good potential for creating ash plants that are less susceptible to ash dieback.


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