Aug 18, 2008
Multistate Tomato Grafting Project has Potential for Growers

Grafting has a lot of potential for tomato growers, especially organic growers and those who use high tunnels. That potential is the impetus behind a complex, multi-state grafting project led by Ohio State University.

According to Matt Kleinhenz, an OSU Extension specialist, the project has two main goals: To answer any question a grower might have about the potential value of grafted plants, and to teach that grower how to graft if he or she wants to learn.

OSU has been studying tomato grafting for years, but its efforts were kicked up a notch last fall, when USDA’s Integrated Organic Program granted it and other universities – North Carolina State University (NCSU), the University of Minnesota, West Virginia State University and Pennsylvania State University – $840,000 over three years to evaluate the performance of grafted material in organic farming systems. OSU, NCSU and the other universities merged their previous grafting studies (all of which had their own funding sources) into one, with each institution focusing on a slightly different component of the overall project – though there is overlap in some cases, Kleinhenz said.

Grafting directly combines the traits of two varieties, one used as a rootstock and the other as a scion. Grafted plants are often more vigorous and resistant to disease and require lower soil nutrient levels than their ungrafted counterparts. It’s a common practice in greenhouse production. In open-field production, grafting is common in parts of Europe and Asia, and interest is growing among organic growers in the Northeast United States, according to Kleinhenz.

“If things turn out as we suspect, (grafting) will become a valuable tool for certain growers,” he said.

Some might even be interested in selling their grafted plants to other growers, he said.

The project will examine the potential of grafting from several angles: genetic, production, yield, quality, economics and others. Investigators are working solely with tomatoes right now, but what they learn probably could be applied to vine crops, eggplant and other crops that are commonly grafted. And though the project is focused on organic production, the information it generates could be useful to conventional growers as well, Kleinhenz said.

The project is still in its first year, and its first phase. The second phase will include on-farm evaluations. Kleinhenz and other investigators are talking to potential organic farmers who would allow open-field and high tunnel trials to take place on their land.

“I don’t want the information to sit on a shelf,” he said. “I want people to use it.”

Among other achievements so far, the Ohio team has produced 5,571 grafted plants, combining Celebrity as a scion with 35 different varieties used as rootstock; has transferred grafted plants to North Carolina and Minnesota for wider evaluation; and has established 144 organic and conventional plots of grafted plants at Ohio research stations, Kleinhenz said.

Studying rootstock genetics is a key part of the project. David Francis, an associate professor in OSU’s Department of Horticulture and Crop Science, focuses on rootstock breeding. He’s used the first year of the study to make crosses and develop a large number of rootstocks, looking for genetic traits that will add vigor to scions. One of the dilemmas he faces is how to increase vigor while making sure fruit quality is preserved. Another is deciding whether to breed a specific rootstock to fight a specific disease, or whether to give the rootstock generalized resistance qualities, Francis said.

The role of Frank Louws, an associate professor of plant pathology at NCSU, in the project is to find tools to manage soilborne pathogens. Conventional growers have traditionally relied on methyl bromide for that, but organic growers have had very few tools, and the heirloom varieties they often sell (for a premium price) possess virtually no genetic resistance to most common soilborne pathogens, he said.

High tunnel growers, with their shortened seasons and increased crop rotations that lead to more disease pressure, could benefit from grafted plants that have strong disease resistance, he said.

The NCSU team had already made progress in managing diseases such as southern bacterial wilt, fusarium wilt and root knot nematode before it merged its efforts with OSU and the other universities, Louws said.

The project has been a great training ground for graduate students, and the investigators have learned much from cooperating with tomato growers, Louws said.

“If grafting is to be successful, it has to be integrated into farm production systems,” he said. “Growers are the best integrators.”




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