Holly's Hunt for a Kūmara Cure

Her research is bringing much-needed new solutions to the troubled vegetable, which holds significant cultural and economic value in Aotearoa. 

The floods enabled the spread of a devastating pathogen. It was one of many significant challenges growers had to face, and the spread of disease and inability to harvest meant any crops they did manage to recover were infected.

It’s been two years since the floods and Holly has been conducting research at Lincoln University to safeguard the industry and to ensure it doesn’t happen again.

Kūmura farms are being infected by a fungal pathogen called Ceratocystis Fimbriata, which causes black rot. They’re also being impacted by tiny soil pests known as root-knot nematodes called Meloidogyne spp. The two problems have been reducing yield and quality of kūmara for many years, as well as making it harder to store for long periods. 

The fungus exists worldwide, but affects different crops depending on the environment. Loving sweet, warm crops, you’ll find it in mangoes in Southeast Asia, taros in Brazil, and in NZ, it's kūmara, being grown in the semi-tropical North Island environment.

The industry’s current plan of attack is applying heavy amounts of chemicals to control the spread of the issue. However, that may not be a long-term solution. The pathogen is showing signs of resistance, and the crops can’t be sprayed in wet weather due to leaching. 

When the floods started to hit and the rain wouldn’t stop, Holly and her team were completely unable to treat the crops with chemicals.

“So that's kind of where the questions started.”

Holly came from a marine science background in Ireland. She came for a trip down-under and found herself in a job at a family-owned kūmura farm in Northland, falling in love with the people, the job and the kūmara. But her science-backed brain never shut off and she kept wanting to dig for more. 

She found her place here at Lincoln, completing the Postgraduate Diploma in Horticultural Science but knew there were more questions to answer. 

Now Holly’s looking into whether another fungus could be the solution to their problems. The natural, soil-borne Trichoderma harzianum has potential as a biological control to manage these pests and diseases. Unlike chemical treatments, Trichoderma is environmentally friendly and has already shown promise in protecting other crops from similar issues.

In her study, Holly is testing how well Trichoderma can stop the pathogen as well as the nematodes. She’s also examining how these pests might interact – does one make the other worse? – and how they affect the long-term storage of kūmara after harvest.

After months of preparation, cultivating roots, and some promising experiments, Holly’s first trial outside the lab has begun. She’s carefully potted about a hundred kūmara plants in one of Lincoln’s climate-controlled greenhouses. Some of the plants are treated with Trichoderma, while others aren’t. She’ll soon deliberately infect the plants with the pathogen, and measure how well the treated plants did.

The potential impacts of this research are huge. Her results could help find a safer, more sustainable way to manage pests and diseases in kūmara, which would help maintain the long-term health of the industry.

It could have cultural benefits, as it provides a healthier relationship to the land, she said.

“It leans into the protection of the land. A huge percentage of the population up north are so connected with their whenua. Why are we applying so many chemicals when there may be another way?”

Holly is excited to bring her new research and skills back with her up North, where the commercial kūmura industry is based.

“The growers are doing things the way it’s always been done, just because there’s no research put into it.

“I really want to bring science-backed growth up North, and say ‘these are the hard facts. It’s proven, so let’s change things from how your dad did it.”