GROWING CONCERN: Michelle Bolga from Coastlands Plant Nursery gives these pohutukawa seedlings a clean bill of health. Photo Mark Rieder D9591-03

IT’S neither erotic nor consensual but the fungus that infects certain native trees has mutated and now reproduces sexually as well as by cloning.

Scion researcher Stuart Fraser said this discovery meant the myrtle rust fungus, Austropuccinia psidii, had a better chance to overcome natural plant resistance as well as be more difficult to control by biological or chemical means.

Native plant nurseries in the Eastern Bay may have reason for concern as the discovery means the pace of incursion could increase exponentially.

Coastlands Plant Nursery owner Jo Bonner said nurseries and garden centres were still dealing with the risk of myrtle rust and taking extraordinary steps to keep it under control.

“We have to apply more pesticides to mitigate the possibility of it arriving here,” she said.

“We follow the NZPPI biosecurity scheme where we have documentation and lists of pesticides we can use.”

The fungus can be carried by wind (the hypothesis is that it is how it arrived from Australia).

“It can survive for up to 60 days under any conditions so it’s a huge risk long term,” she said.

Some species are especially susceptible to the disease.

“We stopped selling pohutukawa for a while because we didn’t know how badly it was going to affect them,” she said.

New information indicates that use of proper pesticides mitigates the threat.

“If you use the preventative sprays, that’s the best you can do,” she said.

Documentation is an important aspect to stop the disease from spreading further.

“It’s really important that people buying pohutukawa ask where it came from because they can unknowingly spread the disease.”

And there are no guarantees all these steps will contain the disease.

“Long term, pohutukawa are going to be deeply affected and it could become a real worry,” she said.

Though no infestations have been found in Whakatane district, an isolated case was discovered in the northern section of Matahina forest in early 2018 in an area that has since been logged.

A small infestation was confirmed along the southeast shoreline of Lake Rotoma along with two much larger incursions near Omaio.

People are encouraged to report myrtle rust findings via the iNaturalist website (an online social network of people sharing biodiversity information), where experts can check to confirm whether identification is correct.

As many as 28 observations of myrtle rust in the Bay of Plenty have been logged on the iNaturalist website since March 2018.

Previous research from other parts of the world suggests that the fungus only reproduces clonally. However, this new study of samples from New Zealand and South Africa shows evidence of sexual recombination in addition to cloning.

mark.rieder@thebeacon.co.nz