Sweet potato, or ‘uala, was among the earliest food crops brought to the Hawaiian islands by Polynesian voyagers.
While it is well-suited to the warm, temperate climate, cultivating the plant is not without challenges, including threats from numerous diseases that impact growth and yield.
A University of Hawaii at Manoa lab, located at the College of Tropical Agriculture and Human Resilience facility in Hilo, has been working to tackle this issue by identifying and distributing “clean,” disease-free plants to local farmers.
According to the USDA, the state produced 6.2 million pounds of sweet
potatoes in 2025, grown primarily on Hawaii Island along the Hamakua Coast.
“Most of the (sweet potato) production happens here on the Big Island, so it’s really great that this center is actually here,” said Sharon Wages, an extension agent for CTAHR who is leading the work.
Part of the National Clean Plant Network, the Sweetpotato-Hawaii Center is
the only lab focused on
the vibrant purple-colored Okinawan and Hawaiian heritage ‘uala variety. Another part of the lab’s goal is maintaining and proliferating these signature traits.
“Besides giving the farmers access to clean planting material that’s virus-free, which has shown to have higher yields, we want to really maintain the characteristics of Okinawan: the tan and purple flesh, the uniformity in size, and the deep color,” Wages said. “It’s not just pretty, but that purple color is an antioxidant, so it’s healthy … things with deep-colored pigment are usually good for you.”
The lab was recently awarded $103,000 from the federal government to support these efforts — more than double the budget in previous years.
“With a $30,000 annual
operating budget, progress was very slow. So now that we got that increase of funds, we’re really excited that we can make bigger strides this coming year,” Wages said.
She said her team is in the final phases of evaluating a promising specimen and preparing it for distribution.
“We found a good line, a candidate that we like. It’s uniform, nice color, and so that one — which we call RH, after a local farmer — that’s our top performer, our best marketable looking one,” she said. “So, that’s the one that we’re trying to mass produce. From that one, we’ll grow up the vines and then distribute the vines to the growers.”
She hopes to start distribution, which will be free to farmers, by 2027. While she said it is possible the lab will charge for vine cuttings in the future, the current goal is just to gain feedback and insight from local sweet potato growers.
“We want to monitor the performance in the field,
because we still don’t really have that data,” she said. “We think we have something good in the lab and in tissue cultures, but then they’re going to give us valuable feedback.”
Achyut Adhikari, one of the researchers working in the lab, has done much of the work of screening different sweet potato samples for diseases and “cleaning” them through various
approaches.
“Once we identify which varieties have what viruses, then we go and proceed to the elimination part, where we use thermal therapy. Or there are few chemical treatments that are available that will increase the growth of the shoot, and we cut the part where viruses are not yet there, and then try to restart it. That’s the process of cleaning,” he said.
Compared to damage from insects and other pests, the impact of diseases on sweet potatoes is not always as obvious, but can still be devastating to crops — resulting in a reduction in yield of between 10% to 50% depending on the type and number of diseases — even though the plants may look healthy.
“They are like these silent killers … they are prevalent, and farmers do not know that because it is not apparent,” Adhikari said. “Other problems like weevils and nematodes, they are visible, and then (farmers) are
seeing those yield decreases … but viruses are also contributing.”
While Adhikari and Wages both acknowledged the plants can, and likely will, get re-infected with the diseases once planted, they said providing healthy ones to start with goes a long way.
“You want to start clean. Once you start with sub-par planting material, it’s that much more of a loss to the farmer,” Wages said. “And in Hawaii, the margin of profit is shrinking, and so whatever we can do to help growers, it’s going to come down to the dollar for them.”
She hopes that the project can serve as a model for the university to be central in the distribution of other clean plants in the future.
