Inducing Disease Resistance and Increased Production in Organic Heirloom Tomato Production Through Grafting

Inducing Disease Resistance and Increased Production in Organic Heirloom Tomato Production Through Grafting

Summary

In 2006, the utility of grafting to manage soilborne disease in heirloom tomato production was shown. Similarly to 2005, CRA 66 and Hawaii 7996 were effective for managing bacterial wilt. ‘Maxifort’ and ‘Robusta’ rootstock were able to control fusarium wilt. A preliminary trial indicated that the use of ‘Maxifort’ rootstock may compensate for lack of rotation in areas infested with verticillium wilt. In one trial, ‘Maxifort’ was able to significantly increase yields under standard and twin-row trellis systems even with little disease pressure from soilborne pathogens. A preliminary study showed that grafting may also induce endogenous defense pathways.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Field trials in 2006 showed that grafting is instrumental for management of soilborne disease in heirloom tomato. This work was highlighted though extension, and made a strong impact on organic and conventional growers both regionally and nationally. Data from field trials was compiled and Cary Rivard successfully defended his MS thesis in December, 2006. Furthermore, a real-time RT PCR protocol was developed to monitor the expression of defense genes in tomato as a result of grafting. This protocol will be utilized further in the spring/summer of 2007 to support preliminary evidence, and plot a time course for defense gene expression.

Impacts and Contributions/Outcomes

In 2006, a holistic research program showed how grafting could be used to manage soilborne disease in naturally-infested soils. Cary Rivard compiled this research for his MS thesis, and it is currently being prepared for publication in a refereed journal. Cary authored an extension factsheet (NC CES AG-675), and has presented his expertise in this area at eleven national, regional, and local venues in 2006. Furthermore, he has maintained a website to disseminate information and resources for growers. These avenues of communication have been well-received, and this research provides an excellent knowledge-base, complementary to the growing interest in this area.

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