By Jerry Jackson
Vegetable grafting is undergoing rigorous study in a number of states, including Florida, in an ongoing effort by scientists to grow more and better tomatoes, melons and other crops. But the technique pioneered in Asian countries has been slow to take root in the United States and remains more of a lab subject than mainstream practice—at least in the field.
That could change in the coming years as soil fumigants are phased out or sharply curtailed and farmers look for other ways to beat old foes such as Fusarium wilt and root-knot nematodes.
Grafting—the technique of splicing the scion, or top of one plant, to the hardy rootstock of another plant—has been used successfully by citrus growers and other tree-crop producers for generations.
In countries such as Japan and Korea, grafting of squash, watermelons and other tender crops has been practiced for many decades, in part because in those countries farmland is scarce and soilborne diseases are even more of a problem than in the United States
Bob Poklemba, manager of Redi-Plants Corp., a south Florida tomato transplant producer for tomato grower Six L’s, says grafting holds promise but is still too costly to make inroads into Florida’s tomato fields. “I don’t think it has a place in our own operations right now,” Poklemba says. “We use a million plants a week. It’s just too costly to make that many plants” through grafting, he says.
A grafted tomato plant for transplanting costs about $1, he says, while regular transplants typically cost less than 5 cents per plant. But Poklemba, who’s based in Naples, quickly adds that grafting can be a viable alternative for at least some smaller tomato field operations in the Carolinas, Tennessee, Virginia and other states where soil might be infested with bacterial wilt.
Grafted plants with resistant rootstocks can make the land useable for production. Florida does not yet have a problem with bacterial wilt, Poklemba says, so there is no economic reason to spend more for grafted transplants on that basis. There are other potential benefits, though.
Benefits of grafting
Field trials in Virginia showed that the yield from tomato plants grafted with bacterial wilt-resistant rootstock was “significantly greater” than from ungrafted plants, according to a report published last fall during the 25th Annual Tomato Disease Workshop in Wimauma.
The report by researchers from the University of Florida’s Institute of Food and Agricultural Sciences and Virginia Polytechnic Institute concluded that the data show that “grafting holds promise for increasing disease resistance in tomato cultivars as well as increasing the overall productivity of tomato cultivars.”
North Carolina State University researchers came to similar conclusions after a threeyear field trial, noting that, “Because grafting allows for rapid deployment of host resistance into a diversity of production systems, this technology will be important for growers that wish to manage soil borne diseases without the use of chemical fumigants.”
For specialty heirloom tomato producers and high-yield hothouse producers, grafting already is financially feasible and widely practiced.
A lot more work is needed to make grafting economically viable on a large scale in Florida fields, says Monica Ozores- Hampton, a vegetable specialist and assistant professor with IFAS in Immokalee.
With about 40,000 acres of tomatoes, Florida has a lot at stake, along with California, the other major U.S. tomato-producer.
More than a dozen other states grow smaller amounts of tomatoes.
“We are making progress,” Ozores- Hampton says of basic research. “But grafting is very expensive.”
Poklemba says he and other Florida growers support the ongoing research on grafting in part because as soil fumigants such as methyl bromide are removed from the toolbox, the costs to grow tomatoes and other crops rise. And grafted plants become more competitive.
If fewer but hardier grafted plants boost the yield and the expense of soil fumigants are excluded, then the equation shifts more toward grafting despite the higher upfront costs.
Poklemba has grafted some tomato plants to help researchers, such as UF’s Ozores- Hampton and her colleague Xin Zhao, who focuses more on north Florida. Zhao notes in a Tomato Institute Proceedings report in 2008 that good healthy scions united with vigorous rootstocks can produce more and better tomatoes under the right conditions.
Grafting is a way to potentially boost healthful benefits in the crop, such as raising the level of nutrients or antioxidants, and that could provide a marketing edge for producers.
Some growers say they have not seen any increase in yield with grafts, however, and report that undesirable traits can sometimes reduce the quality of the harvest.
Watermelon growers, for example, have reported that the squash and gourd rootstocks that are resistant to soil pests can impart squashlike characteristics to the melons. Undesirable traits may include a tougher rind, and the flesh of the melon may be off-color, or less than bright red.
The National Watermelon Association, in Lakeland, Fla., has been helping fund research into the benefits and limitations of grafting, and the U.S. Department of Agriculture also is vigorously pursuing the topic.
As the availability of fumigants diminishes and soilborne pests continue to spread, experts predict that grafting will become increasingly commonplace in U.S. vegetable and melon fields in the coming years.
The trend will follow orange groves, where hardy rootstocks have kept the multibillion dollar citrus industry thriving for decades.