Ash trees could bounce back from the brink of extinction, having developed a resistance to the deadly Asian beetles that have been attacking them.
Devastated by the chronic fungal disease ‘Ash dieback’ and increasing numbers of invasive pests, the fate of the European Ash had been hanging in the balance.
However, researchers have found the tree’s prospects may be improving, as it has developed ‘moderately good’ resistance to one threat — the Emerald Ash Borer.
Infestation of this invasive beetle from eastern Asia can prove fatal, with the pest have severely affected ash species in the United States and parts of Russia.
Tests on a selection of ash species show that European ash — while not immune to initial attack by the beetle — has the resources to restrict the pest’s development.
Experts also found that the frequency at which the beetle’s larvae develop was much lower in European ash than in the highly-susceptible black ash.
However, European ash exhibited a similar level of resistance to that of the Manchurian ash, which co-exists with the beetle in East Asia.
Ash trees could bounce back from the brink of extinction, having developed a resistance to the deadly Asian beetles, pictured, that have been attacking them
Devastated by the chronic fungal disease ‘Ash dieback’ and increasing numbers of invasive pests, the fate of the European Ash, pictured, had been hanging in the balance
Previously, experts were concerned that if the Emerald Ash Borer arrived in Britain, any native European ash trees that had not already succumbed to ash dieback might have been finished off by the beetles.
According to paper author and plant health expert James Brown of the John Innes Centre in Norwich, however, the picture is now looking more positive.
‘In the long term, we predict that ash in the UK will gradually evolve greater resistance to ash dieback as a result of natural selection,’ he said.
‘We expect that healthy trees may suffer some harm from emerald ash borer, but not be severely damaged.’
The researchers said their ‘cautious optimism’ is tempered, however, by the concern that many individual trees, already weakened by ash dieback, could still perish at the hands of the Emerald Ash Borer.
It is estimated that only around five per of ash trees in Great Britain has a good level of resistance to ash dieback fungus.
Previous studies showed that the normally-resistant Manchurian ash can also become more susceptible to the Emerald Ash Borer when environmentally stressed.
Professor Brown and colleagues found no evidence for genetic variation in responses to the invasive beetle in European ash saplings, which means breeding for resistance against the Emerald Ash Borer may not be an option.
Efforts to protect ash should focus instead on excluding the beetle from areas in need of protection, the team concluded.
Infestation of this invasive beetle from eastern Asia can prove fatal, with the pest have severely affected ash species in the United States and parts of Russia. Pictured, damage to an ash tree caused by the Emerald Ash Borer
Researchers have found the tree’s prospects may be improving, as it has developed ‘moderately good’ resistance to one threat — the Emerald Ash Borer, pictured
‘If the beetle were to arrive in UK it would encounter an ash population weakened by exposure to ash dieback,’ said Professor Brown.
‘The combined effect may prove highly destructive initially to woodland and urban plantings.’
‘The emerald ash borer must be kept out of the UK for as long as possible — particularly by restricting imports of ash wood, both timber and firewood, from areas affected by the Emerald Ash Borer or neighbouring areas.’
The team conducted experiments on ash saplings, under controlled conditions, at the Ohio State University in the United States.
According to paper author and plant health expert James Brown, pictured, of the John Innes Centre in Norwich, the picture is now looking more positive
‘I welcome this latest research from the John Innes Centre, which is good news for the future of our native ash trees and our work to protect those trees showing tolerance to ash dieback,’ said Defra’s Chief Plant Health Officer, Nicola Spence.
‘The Emerald Ash Borer is not present in the UK and there have been no interceptions to date.’
‘We have import controls in place on ash trees and firewood and take a zero-tolerance approach to non-compliance.’
‘We are investing in an early warning system and making a concerted effort to increase preparedness of relevant agencies and stakeholders to ensure a swift and effective response should the pest enter the UK.’
The findings were published in the journal Plants People Planet.
