An Invasive Fungus May Be The Solution in The Campaign Against Chilean Guava in A Polynesian Archipelago

The undesirable myrtle rust recently detected on a New Zealand island can function as biocontrol against the undesirable effects of the fruit-bearing herb native to Chile.

A botanical battle takes place in the remote Chatham Islands, an archipelago 800 kilometers east of New Zealand. Despite the remoteness of the Polynesian archipelago, researchers found samples of myrtle or arrayan rust, an invasive fungus that can kill plants in the myrtle families as well as others, including some iconic local varieties like pōhutukawa and mānuka.

However, specialists in this territory, which has been part of New Zealand since 1842, point out that the presence of this pest may be good news. This is because the fungus has only been found in the Chilean guava (Ugni molinae), a plant whose fruit is used to make jam, but that is also an invasive weed with a high ecological impact.

This is pointed out by Peter de Lange, a researcher with the Beyond Myrtle Rust program of Landcare Research/Manaaki Whenua, who explains that there were no endemic myrtle trees in the Chathams.

“La guayaba chilena ha hecho un desastre absoluto en el extremo norte de la isla, particularmente en las áreas pantanosas. Como se dispersa por las aves, no hay forma de detenerla”.

Peter de Lange, of the programa Beyond Myrtle Rust

“Como la roya del mirto se propaga por el viento y las islas Chatham están a favor del viento de Nueva Zelanda, su llegada era inevitable”, señaló en un reporte preparado por la periodista Amber Allot, del medio neozelandés Stuff, donde desarrolló el tema en un artículo titulado “Deadly plant disease myrtle rust reaches Chatham Islands, but expert says it may be a good thing."

De acuerdo al reporte, hasta ahora, la roya del mirto sólo se había encontrado en plantas de guayaba chilenas. Lange señala que si bien algunos lugareños cosechan la fruta y la utilizaron para mermeladas, dijo que era una “planta increíblemente destructiva desde el punto de vista ecológico”.

“La guayaba chilena ha hecho un desastre absoluto en el extremo norte de la isla, particularmente en las áreas pantanosas. Como se dispersa por las aves, no hay forma de detenerla”.

For its part, myrtle rust on the Chatham Islands can threaten landscape plants and a handful of exotic species of eucalyptus that have been planted, he said.

However, and although this fungus is an unwanted organism according to the Biosafety Law, it could also end up being a naturalized biocontrol agent for Chilean guava and could help save a sensitive ecosystem from an invasion of weeds.

“Necesitábamos un agente de biocontrol para la guayaba chilena, y parece que lo hemos conseguido por accidente”.

So while myrtle rust remains a dangerous disease that threatens New Zealand's taonga species, there is some hope that in this particular case it will end up doing more good than harm.

There is no cure for myrtle rust, he said, and given its wind-dispersible nature in the very windy Chathams, the disease was likely to spread.

So while myrtle rust remains a dangerous disease that threatens New Zealand's taonga species, there is some hope that in this particular case it will end up doing more good than harm.

The Chilean guava is native to Chile and neighboring countries. In South America it is found wild in mountain and temperate forest clearings, is grown commercially, ornamentally and even as an edible hedge in urban areas. In fact, the fruit is highly valued in countries such as the United Kingdom, after Queen Victoria promoted it as one of her favorite fruits during the 19th century: she had the fruit travel almost 500 km to London from the temperate climate of Cornwall, the southernmost point of the island, where it was grown for her table. This article from The Guardian explains how to grow and cook the fruit. "The smell of this delicious fruit gets you keen first, filling your nose with clouds of fragrant strawberry as you pass, tempting you to pick them before they're ready – but let them ripen into mid-autumn, perhaps a little later, and you'll get Chilean guava at its unbelievable best ," the article notes.