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» Grafted tomatoes can be used to help manage soilborne diseases and the effects of abiotic stress.
» Under protected conditions, grafted tomatoes are being used to help support high fruit yield potential over a long season.
» Rootstock/scion combinations adapted to the local conditions should be chosen to address specific production issues.
Grafted tomato seedlings became available in commercial vegetable production in Japan and Korea in the early 1960s, and their commercial use in North America and Europe began in the 1990s.1 Grafted tomatoes were initially used primarily in greenhouse (protected) production; however, grafted seedlings are now used in several production systems, including open-field, high tunnel, low-tech greenhouse, and high-tech glasshouse (soilless cultivation).2,3 The higher cost of grafted seedlings has limited their widespread adoption in some situations. The added cost of using grafted seedlings can be offset by higher yields, increased earliness, the reduced number of plants needed per acre, a reduced need for fertilizers, and elongated cropping cycles resulting from more vigorous root systems.1
Figure 1. Grafted tomatoes result from the union of the stems of scion and rootstock seedlings.
BENEFITS OF GRAFTING
Grafting allows the desirable characteristics of a rootstock variety to be combined with those of a scion variety (Figure 1). Desirable characteristics of rootstocks include potential resistance to diseases and pests, increased root vigor, and more favorable responses to abiotic stresses including high salt levels and temperature and moisture extremes. Increased root vigor can result in enhanced vegetative growth of the scion, increased fruit production, and improved fruit quality. Desirable scion characteristics usually focus on fruit yield and quality factors, as well as canopy architecture, disease resistance, and fruit maturation properties.3,4,5,
Resistance to soilborne diseases is one of the primary reasons for using grafted tomato plants. Disease-resistant rootstock varieties can be selected based on the pathogens present in a field, allowing for use of a scion variety with desirable fruit characteristics. This can help reduce the need for soil fumigation and other pesticide products.5 The use of grafted tomatoes has increased substantially following the elimination of methyl bromide as a soil fumigant.1,2,3,4
ROOTSTOCKS
Rootstocks can be intraspecific, where the rootstock and scion belong to the same species, or they can be interspecific, where the rootstock and scion belong to different species or genera. Many of the rootstocks used with tomatoes are interspecific hybrids (ISHs), such as hybrids of the wild Solanum species S. habrochaites and the domesticated tomato S. lycopersicum.4,6
Not all scion/rootstock combinations work equally well in all situations. In a meta-analysis study that evaluated results from 159 publications, yield levels were found to be affected by specific rootstock/scion pairings, the environment, and the production systems used. A few studies showed minor but significant differences in fruit quality factors, such as acidity, soluble solids, firmness, and taste, with some pairings.4
GRAFTING PROCEDURES
Growers can purchase grafted seedlings or create their own from rootstock and scion seedlings.7 The process involves growing the scion and rootstock seedlings, cutting and uniting the scion tops and rootstock bases, and a post-grafting healing period.5 The conditions for both the scion and rootstock seedlings should be optimized to obtain uniform germination and growth. Because rootstock and scion varieties can have different rates of emergence and development, sowing and grafting schedules may need to be adjusted so that both rootstock and scion stem diameters are similar and within the desired range. Growth rates can be adjusted by regulating temperature, light intensity, fertilization, and irrigation.5,7
Grafting is done when stem diameters are between 1.5 and 3.0 mm. Any rootstock suckers should be removed before grafting. Stems are cut with a sharp blade on an angle to increase the area of stem-to-stem contact. Grafting clips are used to align and support the graft union (Figure 2).5,7
Newly grafted seedings should be held in a moist (85 to 95% RH) environment at temperatures between 72° and 85°F (22° and 29°C) for the first 48 to 72 hours. Temperature fluctuations should be minimal, and the relative humidity should not be allowed to reach 100%. Healing locations should have low light levels for the first few days to reduce water loss. After two to three days, humidity levels should be gradually reduced to around 70%, and light levels should be gradually increased.5
Figure 2. Plastic grafting clips are used to stabilize the graft union until the two stems have joined together.
DISEASE MANAGEMENT
A primary reason for using grafted tomatoes is to help manage soilborne diseases. Many commercially available rootstocks have resistance genes for several common soilborne pathogens and nematodes.1,5 Most commonly available rootstock varieties have high (HR) resistance to Fusarium wilt, races 1 and 2, usually indicated as Fol:1,2, and a few have resistance to race 3 (Fol:3).4 Resistance is also available for bacterial wilt, Fusarium crown and root rot, Verticillium wilt, and tomato mosaic virus. Some studies have shown that yield levels on grafted plants with high levels of resistance in fields infested with the corresponding pathogens are similar to those of plants grown in fields treated with soil fumigants.4,6
Many ISH rootstock varieties provide intermediate resistance (IR) to various species of root-knot nematodes (RKN) conferred by genes at the Mi locus. Some forms of resistance prevent colonization and reproduction of RKN on tomato roots, lowering disease levels and pathogen populations. Other forms of resistance reduce symptom expression and help protect yields but do not inhibit the reproduction of nematodes, which can result in increased RKN populations.6,8
It is best if rootstock-based resistance traits are used as a part of an integrated pest management (IPM) program. Integrating resistance with strategies such as crop rotation, soil fumigation, biofumigation, flooding, and soil solarization can help prevent yield losses and the buildup of pathogen populations. The selection of rootstock varieties should be site-specific and based on the pathogen populations present, local growing conditions, and other factors.6
EFFECTS ON PRODUCTION
Several studies have evaluated the effects of grafting on tomato yield. To help maximize yield potential, the needs of both the rootstock and scion should be optimized. The effects of grafting on yield are clearly apparent when disease-resistant rootstocks are used where there is disease pressure. Grafting is also used to help increase production in the absence of disease, especially in long-season, protected culture systems.9,10 The non-disease related effects on yield in shorter season, open field systems may not be as consistent. One meta-analysis study of 159 publications found that yields of grafted and non-grafted tomatoes were not significantly different in 65% of the reviewed studies.4 However, this analysis did show that specific rootstock/scion pairings did impact yield potential. The benefits of using grafted plants is most evident in long season protected culture systems. Rootstock varieties with larger root systems are used to sustain long-season (up to nine months) crops with extended harvest periods.9,10 This is one reason that a large percentage of protected culture operations used grafted tomato seedlings.
CONCERNS WITH GRAFTING
In addition to the added cost of grafted seedlings, there are some concerns about using grafted tomato plants. One concern is the increased chance of transmitting seedborne diseases. Because two different plants are used for each seedling planted, the chance of transmitting a seedborne disease is doubled. Also, the over-reliance on a relatively small number of rootstock varieties for managing diseases and nematodes increases the risk of developing resistant-breaking strains of these pathogens. Growers should carefully evaluate the various risks and benefits of integrating grafted plants into their tomato production operations and understand that rootstock selections should be based on the specific practices used in the operation, desired varieties of scions, and the biotic and abiotic production conditions.6 Factors such as pruning strategies, fertilization, irrigation schedules, and the length of the harvest period also should be considered.
SOURCES
1 Spano, R., Ferrara, M., Gallitelli, D., and Mascia, T. 2020. The Role of Grafting in the Resistance of Tomato to Viruses. Plants-Basel 9.
2 Thies, J. A. 2021. Grafting for managing vegetable crop pests. Pest Management Science 77:4825-4835.
3 Kyriacou, M. C., Rouphael, Y., Colla, G., Zrenner, R., and Schwarz, D. 2017. Vegetable Grafting: The Implications of a Growing Agronomic Imperative for Vegetable Fruit Quality and Nutritive Value. Frontiers in Plant Science 8.
4 Grieneisen, M. L., Aegerter, B. J., Stoddard, C. S., and Zhang, M. H. 2018. Yield and fruit quality of grafted tomatoes, and their potential for soil fumigant use reduction. A meta-analysis. Agronomy for Sustainable Development 38.
5 Guan, W. and Hallet, S. 2016. Techniques for tomato grafting. Purdue Extension. HO-260-W.
6 Louws, F., Rivard, C., and Kubota, C. 2010. Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds. Scientia Horticulturae 127:127-146.
7 Hu. B., Moyseenko, J., Short, S., Walker, S., and Kleinhenz, M. 2014. Eighteen rootstock and five scion tomato varieties: seedling growth rates before grafting and success in grafting the ninety variety combinations. Midwest Vegetable Trial Report for 2014.
8 Cortada L, Sorribas FJ, Ornat C, Fé Andrés M and Verdejo-Lucas S. 2009. Response of tomato rootstocks carrying the Mi-resistance gene to populations of Meloidogyne arenaria, M incognita and M javanica. Eur J Plant Pathol 124:337– 343.
9 Soare R., Dinu M., Babeanu C. (2018): The effect of using grafted seedlings on the yield and quality of tomatoes grown in greenhouses. Hort. Sci. (Prague), 45: 76–82.
10 Rahmatian, A., Delshad, M., Salehi, R. 2014. Effect of grafting on growth, yield and fruit quality of single and double
ADDITIONAL INFORMATION
Performance may vary from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for information about vegetable production. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, pathologist, and similar professional dealing with vegetable crops.
BAYER GROUP DOES NOT WARRANT THE ACCURACY OF ANY INFORMATION OR TECHNICAL ADVICE PROVIDED HEREIN AND DISCLAIMS ALL LIABILITY FOR ANY CLAIM INVOLVING SUCH INFORMATION OR ADVICE.
6811-118889 Published 1/3/2023