Grafting combines disease-resistant roots with strong yielding plant tops.

Grafting binds disease-resistant roots with robust plant tops.
Image Credit: Peter Kent

CLEMSON — Professor Richard L. Hassell is having a “build a better mousetrap” moment. The world is beating a path to his door. Actually, Hassell, a vegetable specialist at the Clemson University Coastal Research and Education Center in Charleston, is the one beating a path. Hassell is visiting watermelon growers around the world who want to learn how he and his colleagues developed a recently patented process to eliminate regrowth, a major challenge to growing food to feed the world.

Regrowth is a result of grafting, the process of splicing soil-disease resistant roots, the rootstock, of one plant to the fruit-producing top, the scion, of another plant. The plants have to be genetically compatible – relatives – for the graft to work. The technique is vital to combat to plant diseases living in the soil.

The rootstock, however, has a powerful drive to grow its own shoots and leaves. If regrowth occurs, the rootstock will nourish its offshoot, leaving the scion to wither. Farm workers scout the young grafted plants in the greenhouse as well as the fields and pinch off the rootstock’s offspring.

Extension vegetable specialist Richard Hassell shows S.C. State Extension D. J. Johnson how to graft.

Extension vegetable specialist Richard Hassell shows S.C. State Extension agent D. J. Johnson how to graft.
Image Credit: Peter Kent

Watermelons and their kin – melons, squashes and cucumbers — are very susceptible to soil diseases that destroy their vines. Commercial growers around the world plant vast numbers of grafted vegetable plants, making Hassell’s work a major advance, reducing rejection and labor costs.

“We tried a chemical used by tobacco growers to destroy plant suckers,” said Hassell. “We experimented with dilutions and standardized the process. We found that we can apply it to growing tissue in the rootstock, and it will stop regrowth – we call it blinding the plant— 100 percent of the time.”

The method had not been tested with watermelons before. “We applied for a methods patent and received it last year,” Hassell said, adding that research led to another discovery. “We saw how using the plant energy produced by the rootstock could trim the grafting process, furthering total automation”

Hassell has met with growers in Asia, South America, Israel and Australia.

Extension vegetable specialist Gilbert Miller shows binding cuts for the approach method.

Extension vegetable specialist Gilbert Miller finishes a binding for the approach method.
Image Credit: Glenn Spake

For now, he’s home, helping South Carolina farmers and gardeners willing to put their fingers on the line to learn how to graft. A cornucopia of growers — young and old, organic and conventional, rural and urban, more than 40 in all — attended a grafting workshop sponsored by the S.C. Watermelon Association last winter in Columbia.

Using razor blades to cut seedling stems, trainees mixed and matched disease-resistant root bottoms with robust vegetable-growing tops. It required a steady hand and an open mind.

“Grafting is more art than science; it that has to be learned by doing the same thing over and over,” said Hassell. “You have to do it carefully and consistently if you want to get results.”

Hassell, along with Clemson Extension vegetable specialist Gilbert Miller and University of Florida vegetable researcher Josh Freeman, demonstrated grafting methods.

For many grafters-in-training, it was a chance to learn a new technique. Others were there because grafting has a following among organic growers. The disease-tolerant rootstock replaces the use of chemicals. What’s more, research suggests that grafted plants respond better to environmental stresses and produce longer during the growing season than non-grafted plants.

“We do know that grafted watermelons seep less water when cut into pieces,” said Hassell. It’s a boon to retailers who sell packages of cut watermelon.

Larry and Janie Harris are Sumter vegetable growers known for their watermelons. They sell a lot to local supermarkets. “During the season, I take 800 watermelons out of the field every week,” Larry Harris said.

Extension vegetable specialist Gilbert Miller checks a graft by Janie Harris of Sumter County.

Extension vegetable specialist Gilbert Miller checks a graft by Janie Harris of Sumter County.
Image Credit: Peter Kent

Harris and his wife followed along as Extension agent Miller did a show-and-tell for the “approach” method.

Miller made an angle cut down the rootstock stem and then a matching angle cut up toward the leaves on the scion, the vegetable-growing part. The trick is not to cut through the stems, notching them and fitting them together, then wrapping the join with a thin strip of aluminum foil serving as a Band-Aid.

The Harrises gave it go and got a thumbs-up from Miller.

“I’ll try with three plants in the greenhouse,” said Larry Harris. “If they work out, then I’ll try a few more.”

Grafting is not something U.S. growers are about to bet the farm on. Compared to conventional planting, grafting can be expensive, laborious and time-consuming. Most growers opt to go slow, depending on agrichemicals, but the situation is changing.

Clemson plant disease specialist Tony Keinath gave an overview of the diseases in the soil. “There’s no cure for them,” he said. Growers have been able to control disease with chemicals, but some products they have relied on have been taken off the market.

What is saving many growers now is that they can rotate their crops and cultivate new fields. But growers around Charleston and Columbia are finding expansion options curbed as bulldozers, more than tractors, contour the landscape.

Josh Freeman, a University of Florida plant researcher, demonstrated tomato grafting.

Josh Freeman, left, a University of Florida plant researcher, demonstrates tomato grafting.
Image Credit: Peter Kent

“Rural growers still have the space to grow,” said Hamilton Dix III, watermelon grower and association treasurer.

Abundant land is something Korea and Japan do not have. Asia is the home of vegetable grafting, where it started about 60 years ago. With prohibitions on chemicals and no land for crop rotation, Asian growers plant the same crops continually on the same acreage. In Korea, 100 percent of the watermelon plants are grafted.

Plenty of people are something Asia does have. Grafting takes a lot of handwork. It’s one thing for a grower to graft a few hundred plants, but imagine what’s involved to grow thousands of watermelons.

“We don’t have the labor here,” Hassell said. “And we aren’t willing to pay what it would take to do it.”

Labor and costs will decline with new automated grafting equipment and breakthroughs like eliminating regrowth so grafting is expected to grow in this country.

“Everybody wants to know how we do it,” Hassel said.