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Grafting to Improve Organic Vegetable Production in Field and High Tunnel Systems


Unfavorable weather, low soil nutrient levels and disease limit season-long production of high quality, high value organic vegetables in many areas. However, the use of grafting and high tunnels can limit these barriers to the success of organic vegetable farms.<P> Variety development is time-consuming, expensive, and technically-demanding. Grafting, in contrast, quickly and directly combines the traits of rootstocks and scions. In fact, grafting is used to grow fruit and hydroponic greenhouse vegetables worldwide and field-grown vegetables in Asia. However, it is new in U.S. organic vegetable production. <P>Grafted plants often out-perform their non-grafted counterparts in our organic on-farm and on-station plots. Grafted plants (roots and tops) are larger, show less disease, and often dramatically out-yield non-grafted control plants. The superior performance of grafted plants may result from their ability to scavenge nutrients and/or resist disease. <P>We plan to test numerous rootstock-scion combinations in multiple settings (open field, high tunnel; farm, station), identify which combinations work best and why and teach farmers and others how to make and use grafted plants. High tunnels are inexpensive, plastic-covered structures used in Europe, Asia and, increasingly, the U.S., to protect horticultural crops and widen production and marketing windows. High tunnels are much cheaper and simpler to manage than greenhouses but create a protective micro-climate around high value crops, benefitting farmers in numerous ways. Yet, our data and organic high tunnel users that we and others work with indicate that soilborne disease and/or nutrient deficiencies may buildup in high tunnels. Unchecked, soilborne disease and/or nutrient deficiencies may devastate organic farms, particularly those with high tunnels. However, grafting is an exciting potential remedy to various types of crop stress. <P>We aim to facilitate the successful use of grafting in soil-based organic field and high tunnel vegetable production. Certain rootstock-scion combinations may out-perform their non-grafted counterparts in terms of plant vigor, disease resistance, and fruit yield and quality. Therefore, our specific objectives are: <OL> <LI>Develop tomato rootstocks that improve fruit yield and quality; <LI>Explain rootstock, scion, soil and production system effects on plant responses to biological and non-biological stress; <LI>Increase knowledge about grafting and facilitate its successful use on organic farms. What we learn in this project can be applied to many horticultural crops and growing areas, so numerous growers will benefit.

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Non-Technical Summary: Unfavorable weather, low nutrient levels and disease restrict season-long production of high quality, high value organic vegetables. Variety development to alleviate production limitations is time-consuming and expensive. The use of grafting and high tunnels can remove barriers to the success of organic vegetable farms, but information and outreach resources are limiting. Grafting efficiently combines rootstock and scion traits. Grafting is used to grow fruit and hydroponic greenhouse vegetables worldwide and field-grown vegetables in Asia. However, grafting is new in U.S. organic vegetable production. The purpose of these studies is to test numerous grafted tomato plants in multiple settings (field, high tunnel, greenhouse, growth chamber; farm, station), identify which perform best and why, and teach farmers and others how to make and use grafted plants. High tunnels can provide numerous benefits to farmers. Used throughout Europe and Asia, they are increasingly common on U.S. organic farms, especially for tomato production. Yet, data indicate that soilborne disease and/or nutrient deficiencies may buildup in high tunnels. Unchecked, these problems may devastate vegetables produced in high tunnels. The purpose is to test whether grafting can provide a solution to biotic and abiotic crop stress that limit field and high tunnel production. <P> Approach: For Objective 1 we will evaluate experimental and commercial rootstocks in a randomized design with un-grafted and self-grafted checks. Rootstocks will be grafted to two scions and the entire experiment replicated in MN, OH, and NC. High tunnel evaluation will be conducted on a single scion in the first year in Ohio. Second and third year trials will also test a more limited number of rootstocks over a larger number of locations through our network of grower cooperators. Ohio will provide seed for cooperators in MN, NC, WV and PA in years 2 and 3, and grafted plants to OH growers in years 2 and 3. Evaluation will include: yield and quality data (including sensory quality), plant vigor and disease resistance, tolerance to cold stress, hybrid vigor, and economic feasibility. For Objective 2 we will determine if scion performance is determined by improved nutrient transport or host defense signals that are passed from roots through the graft. We will establish greenhouse experiments in NC and OH using soils from six different organic farms. We will choose the two most and two least productive rootstock-scion combinations identified under Objective 1, with 20 plants per treatment. Measurements of soil quality, root disease severity, root biomass, nutrient uptake/sap nutrient levels, shoot biomass, fruit yield, and quality will be made using similar approaches as for Objective 1. We will collect data on pathogen infection levels of the roots and for plant defense responses. Symptoms of root disease are not always visible and we will therefore assess infection of roots using quantitative PCR. To assess induced defenses we will use a functional bioassay using Pseudomonas syringae as a challenge pathogen and real-time PCR to monitor the expression of specific host genes associated with induced plant defenses. To determine the relationships between soil and fruit quality we will measure the chemical characteristics of soils collected from plots in order to build a data set to test for correlations. Soil analysis will include particle size distribution, organic matter, complete elements, and standard tests (e.g. pH, exchangeable P, K, Ca, Mg). The resulting data will be combined with our quality data to test whether rootstocks improve nutrient uptake in organic production environments. For Objective 3 we will expand on-farm evaluations and demonstrations of grafted plants by including sites in OH, WV, MN, and NC and PN. Information regarding the selection of parents and crossing for rootstocks, seed saving and grafting methods will be formatted for dissemination via the web. We will present practical training workshops on grafting, participatory breeding, seed saving and sterilization, greenhouse sanitation and high tunnel use. We anticipate that training sessions will be held in conjunction with annual field days in OH and NC to take advantage of high tunnels, field plots, greenhouse facilities, and classrooms at both locations. Workshops will emphasize grower-oriented topics within participatory breeding (for rootstock development), high tunnel use, and methods for seed saving, grafting, seed sterilization and greenhouse sanitation.

Francis, David
Ohio State University
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