Cracking a tough nut for macadamia growers

Macadamia researchers are breeding thinner shells for bigger kernels and tougher husks for resisting pests. 

Macadamias are Australia’s second-biggest nut export, predicted to be worth $350 million by 2025.

The University of Queensland’s Professor Bruce Topp said these combined attributes would boost Australia’s $270 million industry, which earns $190 million in export income annually.

“Two thirds of every harvested kilogram is in the weight of the macadamias’ extremely tough shells. That’s a lot of wasted productivity,” Professor Topp said.

“The goal for many growers is to produce less shell and more kernel from each nut but with the shell still tough enough to resist pests.”

Macadamias are native to south-east Queensland and northern New South Wales but are grown commercially in places including Hawaii, South Africa and Brazil.

UQ, industry and the Queensland Government are jointly funding the Queensland Alliance for Agriculture and Food Innovation research.

“Tough outer husks help protect the nuts from pests, and thinner, inner shells produce larger nuts and profits,” said Professor Topp (pictured).

“Thinner shells however improve access for the macadamia nut borer, a native pest which causes a lot of damage to young fruit.

UQ's Professor Bruce Topp ... trialling sophisticated genomic technologies in the field

“This requires more on-farm management, but biological control strategies are used widely and successfully.

“Growers introduce wasps to control borer moths and owls to eat rats; rats and cockatoos quickly identify trees with thinner-shelled nuts.”

Professor Topp leads the over-arching $2.2 million, Horticulture Innovation Australia–funded National Macadamia Breeding and Evaluation Program.

“Building on decades of macadamia research, we are trialling sophisticated genomic technologies in the field, aiming to boost Australian macadamia growers’ productivity and profitability,” he said.

Hort Innovation’s Dr Vino Rajandran said the global macadamia industry was currently using cultivars more than 60 years old and just a few generations from the wild.

“As a comparison, almonds have been cultivated for millennia,” Dr Rajandran said.

“Based on other horticultural tree crops, we estimate that the macadamia is only yielding around 30 per cent of its potential.

Macadamias on the tree

“We are identifying molecular markers for key growth and production traits in diverse, wild macadamia samples.

“We hope this research will make Australian-bred macadamia cultivars the commercial, global varieties of choice.”

Macadamias are Australia’s second-biggest nut export, predicted to be worth $350 million by 2025.

Professor Topp said the program also was breeding for genetic resistance to “husk spot”, a fungal disease causing immature nut drop and cutting $10 million from industry profits a year.

It was also breeding smaller, warmer climate-adapted, high-yielding macadamia trees.

This research is funded by Hort Innovation using the Macadamia Research and Development Levy, Australian Government contributions, with support from the Queensland Department of Agriculture and Fisheries and UQ.