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The global macadamia industry may have originated from nuts from a single tree in Queensland which were taken to Hawaii in the 19th century, according to new research. 

University of Queensland horticultural science researcher, Dr Craig Hardner, said that “A tree or perhaps a few trees were taken from near Gympie, and maybe six trees were grown from this sample of nuts”. Dr Hardner, and Dr Catherine Nock from Southern Cross University, studied the structure of the chloroplast genome from the Hawaiian macadamia industry and mapped it back to trees in the wild. 

Those few trees formed the basis of the macadamia industry in Hawaii which now supplies around 70% of all macadamia varieties that are grown in orchards around the world. Dr Hardner said, “Most of the germplasm in Hawaii, and particularly that used extensively throughout the world for commercial production, came from a single population, and possibly even a single tree, at Mooloo, north-west of Gympie”. 

A key finding of the research, which was published in Frontiers in Plant Science, is that significant diversity of wild macadamia has been lost through land clearing since European development. The researchers studied the genetics of trees known to have been planted in the mid to late 1800s which are still alive today, and they are not related to any of the trees they have recently sampled from the wild.

Given this lack of genetic diversity, there is a sense of urgency to preserve wild macadamia trees so we can research their genetics to improve production traits like disease resistance, size and climate adaptability. 

“Understanding the genetic diversity of trees in the wild is important because macadamia is a relatively new crop compared to crops such as peaches, where many centuries of domestication have helped improve important traits,” Dr Hardner said. 

“We could well find that some old macadamia trees growing in people’s backyards might also have this genetic diversity.”

He and Dr Nock are working with the Macadamia Conservation Trust, macadamia industry and other stakeholders to sample old trees for genetics that have been lost to macadamia production systems.

Dr Nock said, “There’s this amazing amount of diversity that’s evolved and adapted over probably 30 million years that’s there that we can use in future. It’s rare to be able to pinpoint the origins of a crop’s domestication.”

Denise Bond, Macadamia Conservation Trust, said the hunt continues to find and preserve as many of the old and wild trees as possible and has urged people to get involved. 

Above: Dr Craig Hardner, pictured with the world’s oldest living cultivated macadamia tree, planted in the Brisbane Botanical Gardens in 1858. Photo: UQ

Source/credits:

This research was funded by The University of Queensland, Hort Innovation, Department of Agriculture and Fisheries, and Churchill Trust.

Click here for the ABC Rural article.