Inducing Disease Resistance and Increased Production in Organic Heirloom Tomato Production Through Grafting
In 2005, three field trials examined the affect of grafting on heirloom tomato production in NC. Two on-farm trials utilized CRA 66 and Hawaii 7996 as resistant rootstocks for bacterial wilt (Ralstonia solanacearum). Heavy disease pressure led to >85% mortality among non-grafted and self-grafted controls. Resistant rootstock treatments showed 100% survivability and yields were significantly greater among resistant rootstock treatments. Plant growth analysis indicated that CRA 66 was superior in the field compared to Hawaii 7996. The CEFS trial in Goldsboro, NC indicated the importance of alternative training methods when utilizing hybrid rootstock for increased productivity under organic management.
The objectives of this project are three-fold:
1) An evaluation of rootstock/scion combinations will be carried out in North Carolina through field trials as well as greenhouse trials. Grafted heirloom tomatoes have been planted in the field where bacterial wilt incidence is historically high. Data will be collected pertaining to disease incidence as well as yield and fruit quality. Furthermore, production techniques will be analyzed in an effort to increase yield on a per-plant basis, thereby offsetting the added cost of using grafted transplants. The expected outcomes of this aspect are increased disease resistance in areas where bacterial wilt pressure is high and increased productivity even in the absence of disease. The practical application of this technique and its success will be evaluated and manipulated in order to cater to the success of North Carolina farmers.
2) To determine the efficacy of induced resistance mechanisms when heirloom scion are grafted onto resistant rootstocks. Many of the signaling systems that occur in tomatoes are based around hormones and other compounds that are produced in the roots. This idea may have significant impacts on the ability of specialized rootstocks to induce resistance to foliar diseases in the future. This project is an outstanding candidate for this type of research as the tomato has been used as a model for both the Systemic Acquired Resistance and Induced Systemic Resistance mechanisms. Therefore, many of the physiological mechanisms that are required for this type of inquiry have been previously characterized. We hypothesize, that by understanding how a grafted plant communicates the expression of certain genes throughout its entirety, we may be able to better identify the mechanisms which lead to resistance. This work will lead to a knowledge base to direct this technology through breeding and other cultural techniques.
3) To communicate the results and ideas behind this research through extension and education. An active role will be taken in an effort to introduce farmers as well as extension agents to this technology. Demonstration plots will be used to illustrate the benefits of grafting directly. Grower workshops and training seminars will be conducted in order to show farmers how to graft their own transplants. Finally, we will construct extension publications that describe both the grafting technique and identify resistant lines suitable for rootstock. As this technology is relatively unknown in the United States, it is fundamental that the results of this research are made available through grower workshops and publications.
In 2005, a protocol was established for graft production and several field trials were carried out. Field trials indicated the importance of “systems management” as alternative training methods indicated dramatic yield increases when utilizing hybrid rootstock (Maxifort). In 2006, field trials will be repeated and expounded upon in order to determine not only how grafting can reduce soilborne disease incidence in the field, but also how these rootstocks can be taken full adavantage of in order increase crop productivity. Additionally, growth chamber studies this summer will investigate the basic physiological events that may be occuring during the grafting process.
Impacts and Contributions/Outcomes
Not only has this research led to an increase in the academic community, it has also been passed along to local growers through extension. In November 2005, a 75 minute grafting workshop was led by Cary Rivard during the Carolina Farm Stewardship Association 2005 Sustainable Agriculture Conference. Cary led a similar program at the Regional Greenhouse Workshop in Fletcher, NC. Furthermore, an extension publication has been distributed at each of these events, and is currently under review for final publication. Organic growers in NC are very excited and receptive to hear about grafting technology as it applies to heirloom production. Finally, an informational website has been posted (www4.ncsu.edu/~clrivard) regarding this research. Through this site, a number of growers, both domestic and international, have made contact to inquire about vegetable grafting.
North Carolina State University
Department of Plant Pathology
Campus Box 7616, Gardner Hall
Raleigh, NC 27695
Office Phone: 9195156689