Hopes for curbing myrtle rust by fungi

Researchers have identified a parasite that feeds on myrtle rust.

It was a fungus and been found in Taranaki, the Kaimai-Mamaku ranges in the Bay of Plenty, and possibly in the Auckland region, original finder Dr Michael Bartlett, of Scion, said.

He took samples back to the lab, cultured them and sequenced the DNA to show the fungus belongs in the sphaerellopsis genus.

It was found on myrtle rust-infected ramarama, rō hutu and one of the climbing rātās, he said.

‘‘Natural enemies’’ are one of the tools that scientists hope will suppress the devastating effect myrtle rust has on myrtle plants in New Zealand, in addition to chemical agents for example.

Myrtle rust is a fungal disease that spreads microscopic spores via the wind, although the spores can travel in soil and clothes. It only affected myrtles, but that plant family is large and includes pōhutukawa, rātā, mānuka and ramarama along with commercially valuable exotics such as eucalyptus and feijoa.

The rust is a huge threat in the North Island and top of the South Island. Canterbury and southerly provinces are also susceptible, but at less risk due to cold.

The recently discovered parasite was the second known natural enemy of the rust in this country. In 2018, recent graduate Roanne Sutherland found larvae eating myrtle rust on plants in the Rotorua area. The larvae had turned orange from the distinctive colour created by the rust.

The larvae grew up to be gall midges – a type of fly – and in June they were scientifically described in the peer-reviewed journal New Zealand Entomologist.

The researchers, with Sutherland as second author, thought the larvae were probably New Zealand natives that naturally fed on other fungi and started to eat myrtle rust after it was detected in New Zealand in 2017.

The sphaerellopsis fungi found by Bartlett and colleagues was widespread globally, but probably naturally found here, he said. It had probably ‘‘been here for a long time’’.

Being native or natural to Aotearoa was useful for biocontrol – using one living organism to control another. ‘‘It is a way to control weeds and pests by introducing a natural enemy or predator into the environment,’’ according to the Environmental Protection Authority.

If the biocontrol was natural to New Zealand, then the regulations might be less stringent than if the biocontrol was an exotic species from overseas.