Can genes save our trees?

From flying insects to the trees they buzz around, scientists are turning to genetics to solve one of the most pressing problems affecting UK trees today - infectious diseases, and particularly a nasty fungus known as ash dieback. Richard Buggs - lead researcher at the Royal Botanic Garden in Kew - explains the ‘root’ of the problem to Kat Arney

Richard - In 2012, ash dieback was found in woodlands in Britain for the first time and it had come here from Europe, and we’d seen it actually slowly progressing across Europe over several years. When it arrived in the UK, our government decided to fund quite a lot of research into what we could do about ash dieback.

One of the things that I've been doing is working on the ash trees themselves and sequencing their genome to try to find genes that could be responsible for their interaction with the fungus. We’re hoping that we might be able to breed trees in the future that have a resistance to the fungus.

Kat - Let’s backtrack a little bit – so what causes ash dieback and how is it spread?

Richard - Ash dieback is caused by the fungus Hymenoscyphus fraxineus which is native to Japan and Eastern China. We’re not quite sure how it got over here but here, it’s much more pathogenic against our trees than it is against ash trees in Japan and China, which is why we have a problem.

Kat - Trees don’t get up and move around. They don’t transmit pathogens in the same way that animals might. How is it spread then from tree to tree?

Richard - It’s spread by its spores which infects as they're growing and then when the leaves drop off the trees on the forest floor, you get little mushrooms coming out of the decomposing leaves, and those spread the spores that then go often and infect other trees.

Kat - So how are you trying to map the genetics of the ash trees to try and figure out how they are interacting with this fungus?

Richard - It’s relatively easy now to sequence a new genome. Actually, it took us a couple of years. We’ve published that very recently. We’re taking two approaches to identify genes for low susceptibility to ash dieback in ash trees. One is to look at other ash species from around the world, particularly one that’s from China and Japan which seem to have natural resistance to ash dieback, and we’re using a phylogenetic approach with them.

So, we’ve sequenced the genome of every tree – every ash species around the world that we can get hold of and we’re drawing a phylogenetic tree for every gene in the genome and looking for those genes which have a gene tree that fits with the pattern of susceptibility or zero susceptibility in the whole genus, the whole ash genus among all of these species to try to identify our genes for low susceptibility.

Kat - So you're trying to look for kind of suspect genes that always turn up in the populations that are resistant to the fungus and seem to be somehow missing in the populations that are susceptible to it?

Richard - Yes, variants of genes in different species of ash.

Kat - What's the other approach that you're trying to take?

Richard - The other approach is that Forest Research back in 2012 planted out loads of ash trees – actually, 144,000 ash trees - in trials across the southeast of England. Those trees are now being screened for 5 years against inoculum pressure from these spores of ash dieback. Lots of them have died but some have survived.

So that enables us to pick out British ash trees that seem to have low susceptibility. What we would like to do, if we get funding, is to do a genome wide association study on them to try and find the genes within British ash populations for low susceptibility to ash dieback.

Kat - You're starting to find these British ash trees that are a bit more hardy, can withstand the infection. Can't you just start breeding them and breed them all over the place?

Richard - That is exactly what we’d like to do. But we can accelerate that process if we’ve identified the particular genes involved and then we can do marker-assisted breeding. Another approach is genomic prediction where we don’t have to find the actual genes but we can look at the genetic profile of trees which have higher resistance, and that can accelerate breeding. So of course, breeding trees is a very long process because they live such a long time.

Kat - What about some of the new techniques that I started to see like CRISPR – these genome editing techniques? If you find the gene variations that make a tree more resistant, can't you just cut and paste those in?

Richard - Yeah, that could be a very rapid way to develop trees with resistance to ash dieback. We actually thought about doing some kind of genetic manipulation on ash trees and we surveyed the public. We found that most members of the public didn’t really want genetically modified ash trees in natural woodlands. They might be happy with them in plantations but not in woodlands. So, even if we do take a GM approach, we also need to have a more natural approach just using traditional breeding methods, perhaps accelerated using genetic knowledge but not involving genetic manipulation.

Kat - Will it be fast enough? If this fungus is spreading, if British ash trees are dying, are we going to head for a fallow period where there are no ash trees where we’re trying to breed enough resistant ones to fill the gaps?

Richard - We are likely to see a very significant reduction in our ash populations but given that there are British ash trees that do seem to be able to survive, I think in the long run, we will still have ash in our landscape. One thing we have to be particularly careful about is it’s very tempting for people to chop down ash trees when they don’t need to be chopped down.

So for example, if there's an ash tree that’s dying next to a road, the local council will need to cut down that tree because it could be a risk to life. But when they do that, when they’ve got the road closed, they’ll be very tempted to chop down all of the ash trees on that stretch of road, because they’ll think they’re saving themselves money in the long term. But in fact, they could be taking out some of the trees which have resistance which would actually survive and continue to enhance the environment in their lifetime but also have offspring which maybe have even more resistance.

So, one thing we’re thinking of trying to do is develop a tool so that we can use genetics to predict which trees shouldn’t be cut down so that before a local council, or the highways agency, or network rail start doing very expensive felling, we could actually tell them which trees they don’t need to fell, and they could stay there enhancing the environment and surviving to pass their genes on to the next generation.

Kat - Tie a little yellow ribbon around it or something?

Richard - Yeah, that’s right!

Kat - Richard Buggs, from the Royal Botanic Garden in Kew.