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Compiled by Natalie R. Bumgarner and Matthew D. Kleinhenz GRAFTING GUIDE A Pict

Compiled by Natalie R. Bumgarner and Matthew D. Kleinhenz GRAFTING GUIDE A Pictorial Guide to the Cleft and Splice Graft Methods as Applied to Tomato and Pepper OHIO STATE UNIVERSITY EXTENSION OHIO AGRICULTURAL RESEARCH AND DEVELOPMENT CENTER UNITED STATES DEPARTMENT OF AGRICULTURE Acknowledgments Salaries and research support provided in part by state and federal funds appropriated to the Ohio Agricultural Research and Development Center (OARDC), The Ohio State University and Ohio State University Extension. Work also supported in part by the USDA-Cooperative State Research, Education and Extension Service (Organic Transitions Program Award # 2007-01380; “Grafting to Improve Organic Vegetable Production in Field and High Tunnel Systems”), USDA-National Institute of Food and Agriculture (Specialty Crop Research Initiative Award #2011-51181-30963; “Development of Grafting Technology to Improve Sustainability and Competitiveness of the U.S. Fruiting Vegetable Industry”), OARDC Research Enhancement Competitive Grants Program (Interdisciplinary Team Research Competition; “Genetic Resources for Grafted Vegetable Production”) and Ohio Vegetable and Small Fruit Research and Development Program (“Grafting to Improve Field and High Tunnel Tomato Production”). Use of trade names does not imply endorsement of the products named nor criticism of similar ones not named. The substantial technical contributions of Troy Aldrich, Ken Chamberlain, Dr. Alba Clivati- McIntyre, Dr. David Francis, Bizhen Hu, M.S., Dr. Sally Miller, Jennifer Moyseenko, M.S., Stephanie Short, M.S., Sonia Walker, Jerrod Weyer, Danae Wolfe, and Michelle Young throughout all phases of the development of this document are appreciated. Table of Contents Section Page I. A Quick Guide to Cleft and Splice Grafting ..............................................................................4 II. Planning to Graft.....................................................................................................................7 A. Rootstock Selection.........................................................................................................8 B. USDA-SCRI Grafting Project Rootstock Table.................................................................9 C. Seed-to-Grafted Plant Calculation.................................................................................14 D. Example Age Progression and Growth of Selected Scions and Rootstocks..................15 E. Variation in Stem Development and Growth during Seedling Growth............................16 F. Seed Sanitation (Fact Sheet HYG-3085-05)..................................................................21 III. Preparing to Graft................................................................................................................25 A. Sanitation.......................................................................................................................26 B. Prepare Your Space.......................................................................................................27 C. Grafting Supplies............................................................................................................30 D. Labor..............................................................................................................................31 E. Hand Sanitation..............................................................................................................32 IV. Selecting Plants...................................................................................................................33 V. Grafting Process...................................................................................................................35 A. Types of Grafts...............................................................................................................36 B. Cleft Grafting Overview—Tomato...................................................................................38 C. Splice Grafting Overview—Tomato……………........……………………………………….48 D. Splice Grafting Overview—Pepper.................................................................................55 E. Securing Graft Union......................................................................................................61 VI. Healing and Acclimation..................................................................................................... 63 A. Post-Grafting Environments.............................................................................................65 B. Establishing in the Field .................................................................................................69 VII. Issues to Avoid...................................................................................................................71 A. Reasons for Graft Failure...............................................................................................72 B. Examples of Undesirable Grafting Outcomes.................................................................73 VIII. Image Credits and Citations...............................................................................................77 A Quick Guide to Cleft and Splice Grafting I. Preparation A. Rootstock and scion varieties must be genetically compatible. Therefore, select varieties proven to be compatible through experience or research. B. Note that all the seed sown will not result in a grafted plant suitable for field use. Account for four types of loss when sowing seed: 1. Lack of emergence 2. Seedling quality and survival (some seedlings may perish before grafting or be unsuitable for the process) 3. Graft survival (some grafts will be unsuccessful) 4. Low graft quality (although some grafts “take”, the union is weak or deformed, rendering the plant unfit for use in production). Anticipate these losses and adjust seed sowing rates or the number of plants purchased. C. The following facts influence when and how many seed should be sown: 1. Seedlings grow at different rates depending on variety 2. Rootstock stem diameter must reach a minimum size to graft 3. Rootstock and scion seedling stem diameters must be similar Therefore, multiple sowings are recommended. D. Assemble the following: 1. Labor 2. Scion and rootstock plants (some grafters presort plants according to stem size to save time) 3. New razor blades or cutting tools 4. Clips 5. Sanitation supplies (e.g. alcohol, Physan 20, detergent, oil burners, Clorox, gloves, bench paper, Green Shield) E. Set aside special, clean, climate controlled spaces to: 1. Produce seedlings 2. Assemble grafts 3. Heal and acclimate grafted plants II. Sanitation A. Minimize the onset of seed-borne disease; use clean, high quality, and possibly treated seed, and avoid tobacco use. Seed suppliers and farmers can treat seed using recommended methods involving, for example, hot water and/or chlorine. B. Minimize the transmission of disease; keep seedlings in a properly sanitized space and always wash hands before and after touching seedlings to prevent the mechanical spread of pathogens. C. Minimize the transmission of disease while grafting; always keep work spaces clean with cleaning agents, wear gloves while grafting, and use new or cleaned implements. 4 Splice Graft Method B.1. Using a new, clean razor blade or cutting tool, decapitate rootstock seedling using an angled cut approximately 45 degrees a horizontal cut approximately 5 mm below cotyledons. B.2. Cut scion with razor blade above or below cotyledons at a similar angle to the rootstock cut and where stem is of similar size to rootstock. B.3. Place scion on cut end of rootstock to allow the angles of the two cut edges to match as closely as possible. Cleft Graft Method B.1. Using a new, clean razor blade, decapitate rootstock seedling with a horizontal cut approximately 5 mm below cotyledons. B.2. Bisect the truncated rootstock stem at its widest diameter to a depth of 4 mm. B.3. De-root scion seedlings with a horizontal cut within 5 mm above or below the cotyledons. B.4. Trim the cut surface of the scion seedling to the shape of a wedge containing sides approximately 4 mm long. B.5. Insert the trimmed scion into the vertical slit of the rootstock. III. Grafting Process A. Select healthy rootstock and scion seedlings of a similar stem diameter. C. Secure graft with a clip, tube, or glue. IV. Healing and Acclimation A. Place new grafts in a climate controlled chamber with humidity at 90% (a humidifier may be needed), light reduced by 50% or greater (maintained by shade cloth), and a temperature range of 70–80/84 degrees F night and day for 5–7 days. Bottom watering is suggested in order to reduce stress on the graft union and limit the chance of decay. B. Place week-old grafted plants in a second post-graft chamber to begin transitioning into ambient greenhouse conditions. Bottom watering is still important to reduce stress on the graft union and plants. C. Place two-week-old grafted plants in an area with humidity, light and temperature ranges recommended for acclimating tomato seedlings prior to planting. The same chamber can be modified to accommodate all post-graft healing and acclimation environments. V. Planting A. Plant the grafted plant so that the graft union remains at least 2.5 cm (1 inch) above the soil line. A rule of thumb is “don’t bury the clip,” if it remains. Proper placement of the plant limits root formation from the scion. B. Grafted plants may develop shoots from the rootstock and/or roots from the scion. Observe plants after planting and prune as needed. 5 Planning Healing / Acclimating Splice graft Cleft graft Securing graft union—clips or glue Establishing in field Preparing Selecting plants 6 Planning Healing / Acclimating Splice graft Cleft graft Securing graft union—clips or glue Establishing in field Preparing Selecting plants Variety Selection, Seed Number, Seed Treatment and Sanitation 7 Rootstock Selection Grafted tomato plants have long been a staple in greenhouse production systems; now, their use in soil- based outdoor and high-tunnel ones is rising, too. Moreover, the number of commercially available tomato and pepper rootstocks (RSs) is increasing, perhaps faster than users are becoming familiar with their compatibility and performance when paired with various fruiting, scion varieties. A snapshot survey of the list of commercially available tomato RSs in the U.S. may reveal that most were developed for greenhouse systems or that their parents were. However, that balance is changing. Each year, more open field and high tunnel acres are established with grafted plants. From breeders to farmers, all recognize that RSs must be developed and selected for specific conditions. Greenhouse, high tunnel and field production environments vary—so, it is reasonable to conclude that RSs ideal for each will also. Grafting is a type of organ transplantation. Currently, protocols and parameters for assessing the viability, strength and performance of rootstock-scion combinations are inadequate but improving. Regardless, for growers to succeed, it is clear that: (a) the rootstock and scion must be fully compatible; (b) the “operating room” where grafting occurs and all other materials used in the process must be clean; (c) newly grafted plants must have an opportunity to heal; (d) plants of the new, “hybrid” rootstock-scion combination must out- yield standard, ungrafted plants of the scion; and (e) fruit taken from grafted plants must be at least equal in quality to fruit taken from ungrafted scion plants. In this section, we will focus on rootstock selection. First, we recommend that the grafter-user of grafted tomato and pepper plants consider their production goals, cultivation history, growing conditions and resources. Ask key questions. For example, why do I intend to prepare and use grafted plants? What benefits will grafted plants offer to me? How much time, money, effort and space can I devote to preparing and using grafted plants? What is my expected return on investment? Grafted tomato plants may significantly out-perform their ungrafted scion variety counterparts under a range of field and high-tunnel conditions. However, that superior performance is more likely under uploads/Ingenierie_Lourd/ grafting-guide.pdf