Grafting is a technique whereby the root system (or rootstock) of one plant is fused onto the stem and leaf (or scion) of another plant. The purpose is to match the field performance characteristics (high yield, disease resistance, drought tolerance, etc.) with a fruit that has high market demand.

In a three-year project, Ohio Agricultural Research and Development Center scientists have found success in using the technique to improve tomato cultivars. As a result of the research, three promising rootstocks have been identified that could add to the few commercial rootstocks currently available and expand tomato grafting into such markets as organic and high tunnel tomato production.

“Rootstock breeding programs are aimed at big producers, specifically for the hydroponic vegetable market. There are several rootstocks on the market, but really only two that are considered commercial standards,” said David Francis, an OARDC geneticist. “Our research was aimed at soil-based production, either open field or high tunnel, and targeted organic farms due to the high value of the produce. The results of the research potentially will give growers interested in grafting more rootstock choices.”

Francis bred 46 rootstocks by cross pollination of cultivated and wild tomato species and found that three rootstocks show promise in carrying traits for field performance, such as yield or disease resistance, while producing a desirable, marketable fruit.

“The idea behind developing rootstocks is to produce a plant that has more vigor than the typical tomato, while not losing the fruit characteristics that consumers like,” said Francis. “We were looking for a rootstock that performs consistently better than the non-grafted plant as well as the commercial rootstock standards.”

Francis said that when it comes to rootstock breeding, the key to hybrid vigor rests with the parents selected for crossing.

“The further away in genetic relationship the parents are, the more vigorous the plants tend to be,” said Francis. “That is, two cultivated plants with similar genetic backgrounds will be less vigorous than a cultivated plant crossed to a wild species.” In fact, the three rootstocks that performed the best were all crosses between a wild South American species and a domesticated tomato.

The rootstock breeding research is just one part of a larger grafting project to improve efficiency and productivity in the tomato industry, which was valued at $67.5 million in Ohio last year.

With the 46 rootstocks, Francis was looking for such characteristics as seed size, uniformity of germination, high yields, fruit quality, disease resistance, drought tolerance and fruit size. Ten were eliminated due to poor seed characteristics.

“Of the 36 rootstocks that advanced to the field, we came up with a list of nine that we thought were acceptable in terms of those characteristics, especially yield and quality, but ended up eliminating six of them because they didn’t graft as well as we would have liked,” said Francis. “Certain combinations just don’t graft well.”

After two years of promising results from the three chosen rootstocks, researchers hope to get at least one more year of data from various field locations across the nation before recommending the rootstocks for commercial production.

“If these rootstocks are successful, commercializing them will definitely give growers more choices, especially in an organic production system,” said Francis. “One of the limitations in organic tomato production is weak uptake of nutrients. More vigorous rootstocks can improve the production of quality fruit.”

Francis said he also sees new commercial rootstocks improving organic tomato production from a disease standpoint.

“Growers’ preferred varieties are sometimes heirloom cultivars – old varieties that have very little natural resistance to diseases,” said Francis. “There isn’t as strong an effect when a rootstock is grafted to a hardy scion, but you graft a rootstock to a weak scion and you definitely see an improvement in performance. Resistance to soil-borne diseases and extra vigor helps the plant to stay healthy and that has an impact on overall quality of the crop.”

For more information on grafting, log on to http://oardc.osu.edu/graftingtomato/graft.htm.