Ash dieback, a fungal disease also called Hymenoscyphus fraxineus, has killed off thousands of ash trees in the UK. Thought to have arrived from Denmark, where ash dieback has wiped out 90 per cent of its ashes, it was first reported in Buckinghamshire in 2012. Since then, the disease has made its way across the UK via wind-borne spores, with few areas left unaffected.
Mysteriously, some trees have not been infected – even when they are surrounded by dying specimens, leading scientists to study the genetic markers for these especially tolerant specimens in hopes of finding a cure.
Professor Allan Downie of the John Innes Centre says ‘Because the disease was more advanced in Denmark, we used Danish ash leaves to find a genetic pattern associated with low susceptibility.’ The question was whether or not the genetic patterns for low susceptibility were the same in UK ash trees: ‘UK trees are a little different, we did not know if the Danish genetic markers would work on them.’
“Betty is symbolic of a small population of tolerant trees that could form the basis for rebuilding the ash population”
This is where ‘Betty’, a 200-year-old ash tree in Norfolk, comes in. Betty had been observed for some time as having low levels of ash dieback symptoms. When Downie tested its genes for the dieback tolerance markers, Betty met the criteria for low susceptibility. ‘Betty is important because it gives us confidence that our genetic predictions are working in UK trees’ he says.
Betty is not alone. There are other ashes near to it that also appear to be tolerant to the disease. Downie hopes to figure out what proportion of similarly tolerant trees make up the whole UK population.
‘In some regards, [Betty] is symbolic of a small population of tolerant trees that could form the basis for rebuilding the ash population,’ says Downie, ‘while disease works its way through the susceptible species. What we do not know yet is what proportion of the trees’ offspring inherit the tolerant genes. There is quite a lot still to do, but we can now see a way forward using trees that are much less susceptible to the dieback.’
This was published in the June 2016 edition of Geographical magazine.