Currently a lot of profit potential dies in the field because heirloom cultivars lack genetic disease resistance. Using a new technique called Japanese top-grafting or tube grafting, Rivard is testing rootstock of resistant varieties with cuttings of ‘German Johnson,’ ‘Cherokee Purple,’ ‘Kellogg’s Breakfast’ and other heirloom favorites. The technique is so popular in other countries that Asian and Japanese companies have developed lines just for rootstock.
The project team tested some new rootstocks at the Center for Environmental Farming Systems and on cooperating farms – with good results. “In our bacterial wilt trials, plant mortality from this disease can be as high as 80-100%, yet the heirlooms grafted onto resistant rootstock showed no symptoms of disease throughout the season” says Rivard. In a recent trial, the total yield was 8 to 10 pounds higher per plant than that of non-grafted controls. In this case, grafting with resistant rootstock almost doubled the total yield.
“Similarly, fusarium wilt can be completely controlled using rootstock for heirloom production,” he says. “In non-grafted and self-grafted control plots, fusarium wilt was seen in 45 to 50% of the plants, and with one rootstock, we saw no symptomatic plants in any of the plots.”
Is disease resistance worth the extra cost and labor? “A thorough economic analysis for American production has not been carried out to date,” says Rivard. “One of the focuses of our work is to run economic analyses based upon both sustainable and conventional systems to see where grafting fits in economically for local growers.” A recent study in Morocco showed that grafted transplants can be produced for 38 cents (U.S.) and non-grafted for 19 cents each. Rivard adds that these growers found that with vigorous rootstock, they can reduce the planting density of grafted plants by half compared with non-grafted plants and actually get higher yields per acre. “So in this study, grafting with vigorous rootstock not only pays for itself, but actually increases net income on a per acre basis,” he says. “Canadian nurseries sell grafted transplants for the U.S. greenhouse industry, but their prices seem to be a bit higher ($.75-1.50 per plant).”
Growers of heirloom tomatoes will most likely justify the expense of grafting before growers of hybrids do, according to Rivard. “In our area, small farmers continuously sell heirloom tomatoes at wholesale and retail markets for $2 to $3 per pound, regardless of organic certification. Even at the higher estimated price of grafted transplants, an increase of less than one pound of fruit per plant could potentially offset the cost of grafting for these growers.” Those who grow hybrids or grow on a large scale would need increased yields to mitigate the expense of grafted plants.
Farmer cooperators “have been instrumental in helping us look at grafting through the eyes of a fully functional farming system,” says Rivard. “One thing that has been extremely important for the success of these trials is that the growers have something invested in the trial and the crop that comes off of it. For this reason, the plants and the plots at these smaller farms are always in wonderful shape every time we visit.”
However, working outside the narrow purposes of a research station plot also complicates the project. “One challenge about using a real farm is finding a way to coordinate yield data collection with the growers’ regular harvest schedule,” Rivard says. “Our smaller growers have worked with us very graciously, and actually do most of the yield data collection themselves.
For researchers, this is an extremely powerful system, because we can look at marketable yield and know exactly how much money was generated from each plant within the plot.”
Grafting tomatoes is much easier than most people think, according to Rivard. “A chamber will be required, but these can be built very inexpensively in any type of heated structure, like a greenhouse.” The key, he says, is that direct light be reduced – by shade cloth or a tarp, for example.
For instructions on tomato grafting, see the NCSU extension publication written by Rivard and Louws at
Read more about Rivard’s project, GS05-046, and a related project, LS06-193, in the project database at www.sare.org.
Source: Common Ground, Spring 2008, www.southernsare.uga.edu/commongrnd/08spring.pdf