Grafting plants can solve bacterial wilt problems in a field of tomatoes and can significantly reduce damage from rootknot nematodes, but that doesn’t mean that profit will follow, says Virginia Tech Horticulturist Josh Freeman.

“I’m not an evangelist for grafting, but I can make a field of tomatoes whole by switching from non-grafted transplants to grafted plants.

“We’ve seen tomato fields with 95 percent or higher loss from bacterial wilt and by using grafted plants, we can cut the loss to less than five percent. But, that doesn’t mean the field will be profitable” the Virginia Tech specialist says.

Freeman, who works extensively with growers on Virginia’s Eastern Shore, says he got interested in grafting because of a worsening problem with bacterial wilt.

Fumigants are widely used, but new regulations have reduced fumigant use rates and growers and not getting the same results they used to with high rates of methyl bromide. 

Using soil fumigants has become a costly proposition and many small growers simply cannot afford them anymore. “We seem to be in the waning era of using these soil applied pesticides for many growers,” he says.

“With fumigants, we are buying time on a tomato crop. By the time the grower gets three-fourths or so through the growing season, roots have made it out of the fumigated area and the crop is exposed to diseases that can take out virtually all the production.”

Virginia growers, Freeman says, have no good varietal options that have resistance to bacterial wilt.

With resistant cultivars, growers get softer, small fruit and other negative qualities that can make their crop unmarketable. So, in cases like that grafting is an obvious answer.

The big downside of grafting is cost.

For a small vegetable grower the cost of grafted transplants may be 45 cents or so per plant if they graft themselves versus 10-12 cents for seeded transplants.

However, in a bigger commercial operation, the cost of commercially produced grafted transplants may be 75 cents or more versus 8-10 cents for seeded transplants.

Big upside

“The big upside of grafted transplants is that we can build a plant that has a disease resistance package tailor made for a specific field and a specific combination of disease problems.

“It may take a plant breeder decades to get the same disease package into a plant and we can do it with grafting in a matter of minutes,” Freeman says.

Grafting is a natural process that joins the top part of one plant (scion) to the root system of another plant (rootstock) without any genetic modification. As tissues heal, the two plants fuse, combining the rootstock’s vigor and disease résistance with the scion’s exceptional fruit quality and flavor.

Some of the benefits of transplants include:

• Stronger, more vigorous plants;

• Improved yields in disease prone areas;

• Superior defenses against soil-borne diseases and pests, including nematodes.

North Carolina State University Horticulturist Frank Louws is spearheading a cooperative effort among several universities, growers and agri-industry leaders to develop grafting of plants for various vegetable crops grown in the U.S.

“As part of a large grant, we held an organizational meeting recently, expecting a couple dozen people from the Southeast to attend.

“We had more than 100 people from all over the world attend our meeting. That’s an indication of the interest the vegetable industry has in grafting,” Louws says.

“Grafting technology can produce more reliable plants than conventional seeding — we know that and can demonstrate that in the field,” he adds. “What we don’t know is how to provide enough plants at a low enough cost to make the technology profitable on a wide scale of commercial production.”

One of the markets to profit most consistently from grafting is organic production of heirloom tomatoes.

Researchers at North Carolina State Universityfound through a series of field tests that heirloom tomato varieties grafted onto tomato root and main stem stock of modern disease-resistant varieties provided an effective management tool for growing heirlooms where locally existing diseases would otherwise preclude or greatly diminish the crop yield.

Improved heirloom yields

Grafting to sturdy root and main stem stock also improved the yields of the heirloom tomato varieties where there was not disease pressure, which makes growing unique and interesting tomatoes — even by organic methods — considerably more economically productive for small market growers, and allows home gardeners a wider choice of tomato selections.

One company, Mighty ‘Mato has taken grafting to a new level for both organic and commercial growers.

Indiana-based Mighty ‘Mato is the first national brand featuring grafted tomatoes and grafted vegetables. Worldwide, over 1 billion vegetables are grafted annually, primarily for commercial production.

“My advice to commercial vegetable growers, who are interested in looking at grafting, is to move forward with trepidation.

“We don’t have enough testing done to know a lot about how one rootstock will perform under different production and environmental conditions,” Freeman says.

All rootstocks are not created equal. Some claim to have great resistance to bacterial wilt, for example, but when he put them in field tests in Eastern Virginia they failed. “We’re just not in a position to have looked at enough rootstocks to know which is going to work over a wide production area,” he adds.

Freeman says researchers know even less about vigor than about disease packages on various rootstocks.

“If you are growing in a high tunnel versus an open field, you are looking for different things and the same rootstock will likely have different results from one growing system to the other.

“In a high tunnel situation, growers are usually looking for 10-12 harvests and plant vigor over a long growing season is important.”

“In an open field production, uniformity may be more important because the grower is harvesting fewer times.”

Louws and Freeman agree that the key to including grafting into commercial operations is to know the problem.

“If a grower knows for sure there is a certain disease problem in a field of vegetables, most likely we can solve his or her problem with grafted plants.

“Again, whether fixing the problem means fixing profitability depends on a lot of things and successful grafting of plants may make the profitability problem worse, Freeman says.

“Grafting is already a routine part of several small, mostly organic vegetable producers in North Carolina, so we know it can work in some operations.

“When we go to commercial production, there is a whole new set of challenges, many of which are being addressed by the multi-state, multi-year grafting project that is currently under way in North Carolina and a number of other cooperating states,” Louws adds.

rroberrson@farmpress.com