Final Report for LS06-193
In a 2006 controlled environment experiment, shoot and root biomass, height and most total tissue nutrient concentrations were greater in grafted treatments. In replicated 2007-2008 field and high tunnel trials at the Center for Environmental Farming Systems, Goldsboro, NC, yields of grafted organic heirloom tomatoes were higher than non-grafts. Both years fruit weight and fruit number were higher and production peaked three weeks earlier in the tunnel system than the field. In on-farm trials, soilborne diseases such as bacterial wilt, root-knot nematode, Fusarium wilt and southern stem blight were effectively managed utilizing rootstocks.
Tables, appendices with figures or graphs mentioned in this report
are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
email@example.com for a hard copy.
- 1. Improve grafting, acclimation and transplanting techniques.
2. Select appropriate rootstocks for root-knot nematodes and other soilborne diseases.
3. Select appropriate rootstocks for increased nutrient uptake efficiency and other horticulturally valuable traits, such as fruit quality, earliness, vigor, and resistance to pests.
4. Test training and establishment techniques for grafted rootstocks, including single and multiple head systems.
5. Compare performance of scions grafted onto resistant rootstocks, self-grafted and non-grafted controls under realistic conditions of soilborne disease pressure.
6. Compare performance of scions grafted onto resistant rootstocks, self-grafted and non-grafted controls under optimal growing conditions on an organic research station.
7. Evaluate a grafted rootstock-high tunnel tomato system for feasibility, including a preliminary assessment of the economics. This system will be compared with open-field production.
8. Identify promising avenues for future research and development.
The purpose of this project is to develop research-based information on an economically viable system for tomato production without the use of fumigants and not dependent on fungicides for early blight control. Although solarization, cover crops, incorporation of organic materials, biofumigants and rotation can effectively control nematodes and soilborne diseases as well as improve soil fertility, their implementation is not always practical or completely successful on small acreages and organic farms in the southern region. This is especially true for diseases such as Bacterial wilt (Ralstonia [formerly Pseudomonas] solanacearum), Fusarium wilt (Fusarium oxysporum ) or Verticillium wilt (Verticillium dahliae) where even a rotation as long as 7 years might not be sufficient to eliminate pathogenicity and for soil pathogens with many hosts.
For example, Bacterial wilt affects all plants in the Solanaceae (tomatoes, peppers, potatoes, eggplants), is not controlled by rotation and is worse in fields where nematodes are present. In addition, soil improvement requires several years in organic and sustainable farming systems, so yields may decrease temporarily on farms transitioning away from high analysis fertilizers to organic inputs. Grafting of susceptible scions (the cultivar grafted as a top) onto resistant rootstocks is widely practiced in Japan, Korea and many parts of Asia (Lee, 2003; Oda, 2005; Lee et al. 1998). It offers a potentially attractive alternative or supplement to fumigation by conventional growers and long rotations or solarization for by organic growers, but has not been field tested in North America on any crops. In Cyprus, a combination of grafting eggplants on resistant rootstocks coupled with soil solarization was found to be more effective in preventing damage from Verticllium wilt, corky root rot and root-knot nematodes than either practice by itself. In addition the combination had an additive effect on yield, resulting in higher yield than either method alone (Ioannou, 2001).
In Hawaii, trials on an organic farm with high rates of bacterial wilt, showed grafting 'Big Beef' on a Lycopersicon pimpinellifolium rootstock resulted in a 97% survival rate against bacterial wilt with 95% of the grafts also being successful. Yields and percentage marketable fruit were also good in the grafted transplants. Little efficacy was seen in reducing incidence of bacterial wilt from other alternative practices. These practices included: organic matter (steer manure and composted macadamia nut husks) and lime additions; Biotron soil inoculant (an additive containing 25 beneficial bacterial, fungi, enzymes, algae and yeasts); Mycostop (product containing the soil bacteria Streptomyces griseoviridis, alleged to provide biological protection from numerous diseases); and Intercept (fungicide and nematicide containing the soil bacteria Burkholderia [formerly Pseudomonas] cepacia). The trial also included and 8 resistant cultivars. Highest survival rates against bacterial wilt (100%) were seen in two of the resistant cultivars, the remainder having only 64-86% survival from bacterial wilt. However, fruit quality and yields were only acceptable in 1 of the 8 resistant cultivars.
Besides disease and nematode resistance, many other benefits have been reported in grafted plants. Lee et al. (1998) reported disease tolerance, low and high temperature tolerance, enhanced nutrient uptake, salt tolerance, increased fertilizer efficiency, wet soil tolerance, enhanced water uptake, root nodulation, winter hardiness, xylem sap composition differences and nematode resistance as direct responses to grafting.
Indirect responses included shoot growth promotion, decreases in occurrence of physiological disorders, fruit yield and quality improvements, earliness, size control and extended harvest period. The reason for these benefits is not well understood, but could involve some form of Systemic Acquired Resistance (SAR) or Induced Systemic Resistance (ISR). SAR and ISR are two different physiological signal transduction pathways that affect plant growth and disease resistance.
Watermelon grafted on gourd (Langenaria) type rootstocks, flowered about 10 days earlier, showed more vigorous vegetative growth than controls, up to 148% higher fresh weights and 27-106% higher yield than controls (Yetisir and Sari, 2003). In the US, the Agricultural Research Service has been working on a project since 2002 that involves grafting watermelons onto gourd or squash rootstock. They found grafting increased the fruit firmness by 30 to 100%, while maintaining sugar and lycopene content. Grafted watermelons also were resistant to all 3 races of Fusarium, compared to cultivars with varying resistance to only two races of Fusarium. Early results on the watermelon study also indicate that farmers may require fewer grafted pants per acre to produce the same yields and may need less fertilizer per acre (Agricultural Research p. 8-9, July 2005 and www.lane-ag.org/h2omelon/watermelon.htm)
In the US and Canada, grafting of very young tomato seedlings is already widely utilized in inert media (rockwool) by large commercial greenhouse tomato operations growing plants in inert media (rockwool) but is also used for soil production by organic greenhouse tomato growers in New England and Quebec for soil production (Manix, 2003). In rockwool production, grafting is utilized to improve plant vigor and confer resistance to disease and insect pressures. Specifically, the added plant vigor is thought to confer resistance to the pepino mosaic virus transmitted by silverleaf whiteflies (Gretchen Raymond, DeRuiter seeds, personal communication). This has not been tested in controlled experiments, however. In organic soil operations, it grafting is utilized to protect against soil diseases (Manix, 2003). Grafting has not been field-tested in North America for field production, however, and even though it is widely practiced in tomato production greenhouses there have been no reports from controlled experiments in the US or Canada. Although field applicability and potential economics in the field are difficult to predict, grafting could offer some interesting opportunities for organic growers who direct market.
For market gardeners, availability of resistant rootstocks would enable field growers to select from among a wider range of scions, including locally adapted inbreds and heirloom lines which lack multiple disease resistances. Grafting is a relatively simple procedure that could be conducted on-farm after training. There are no commercial sources of grafted transplants in the US for either greenhouse or field production, however. Once recommendations are developed from our project, and a market established, both organic and conventional production of grafted transplants would offer a good opportunity for local enterprise development. Several greenhouse growers, including one of the project participants have expressed an interest in developing a commercial facility to produce grafted seedling. Although the process is time-consuming for untrained workers, a trained worker or small team can graft several hundred transplants per hour, and transplanting equipment is available commercially. In Korea, grafting efficiency for tomato is 60-100 plants/h for a team of 3-4 workers using the cleft grafting method (Lee, 1998). Using grafting machines, from 600-1000 tomato seedlings can be grafted per hour. Although New England organic growers have had good success with grafting (e.g. Manix, 2003), specialized transplant production enterprises offering custom production of grafted transplants should increase adoption of this technique by growers. Thus the operation could be scaled up, and efficiencies of scale achieved.
Grafted organic transplants will still be up to 3 times more expensive than conventional transplants (Lee, 1998), which cost only a few cents each, but could reduce other costs. For example, conventional growers spend up to $2,000 per acre to fumigate with methyl bromide, and it is unlikely that alternative fumigants being evaluated as methyl bromide alternatives will be significantly less expensive. For organic growers, there are also costs involved in rotating a field out of production, or utilizing cover crops and biofumigants as a primary pest suppression strategy, especially on small acreages. Rootstocks could also reduce costs for fertilizers and pesticides, although these benefits have yet to be documented in the US. Some changes in the farming system may be required to make the use of grafted plants economical, however. For example, with a more vigorous rootstock, it may be possible to increase plant spacing, thus reducing the number of transplants required per acre, and decreasing plant establishment costs. For greenhouse growers, the transplant costs are not significantly higher for grafted transplants because the scion is topped early in development and two leaders allowed to develop instead of the usual single shoot. Thus one rootstock is used to support two plants. This is done both to reduce transplant costs and because the rootstocks are vigorous enough to support two plants. In the trellis tomato system as practiced in western NC, plants grown on vigorous rootstocks might require less pruning as well as allow for wider spacings, thus decreasing labor costs for planting and pruning.
Changes in production, such as the use of grafted plants, require a systems approach to enhancing crop productivity, economic viability and sustainability. In hot and wet climates, rain shelters have been shown to increase summer yields when used in combination with grafted plants (Black et al., 2003). High tunnels are also expected to offer some protection in NC against both early blight and fruit cracking. Fruit cracking (Peet, 1992) in the field usually results from excess rainfall, especially from late summer and early fall tropical storms and after dry period. Fall is a time at which demand for high quality tomatoes at farmers' markets is often high. For NC organic growers, yield is often reduced in the late season by early blight and fruit cracking. In fall 2004, simultaneous tomato crop failures in both California and Florida drastically reduced the supply from the field, creating high demand for good quality tomatoes for greenhouse and other growers with a fall crop. The Florida crop was also adversely impacted by Wilma in fall 2005. By coupling grafted plants with high tunnels to reduce susceptibility to early blight and fruit cracking and to increase early production, we hope to develop research-based information on an economically viable system for tomato production without the use of fumigants and not dependent on fungicides for early blight control.
• Black, L.L., Wu, D.L., Want, J.F., Kalb, T.l Abbass, D. and J.H. Chen. Grafting tomatoes for production in the hot-wet season. International Cooperators' Guide ABRDC pub#03-551. May 2003. AVRDC, Shanhua, Taiwan.
• Chung, H.D.,Youn, S.J. and Choi, Y.J. 1997. Effects of rootstocks on seedling growth and prevention of root-rot Fusarium wilt (race J3) in different tomato cultivars. J. Kor. Soc. Hort. Sci. 38: 327-332
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• Hussey, RS; Barker, KR. 1973. Comparison of methods of collecting inocula of meloidogyne-spp, including a new technique. Plant Disease Reporter 57: 1025-1028
• Ioannou, N. 2001. Integrating soil solarization with grafting on resistant rootstocks for management of soil-borne pathogens of eggplants.
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• Manix, J. 2003. Tomato Grafting. New England Vegetable & Berry Conference 2003 Proceedings. Dec. 16, Protland, ME. Ww.nevbc.org/proceedings.html.
• Oda (2005) Grafting of vegetables to improve greenhouse production. Food & Fertilizer Technology Center. www.agnet.org/library/eb480.html.
• Ornat, C; Verdejo-Lucas, S; Sorribas, FJ. 2001. A population of Meloidogyne javanica in Spain virulent to the Mi resistance gene in tomato. Plant Pathology 85: 271-276.
• Peet, M.M. 1992. Fruit cracking in tomato. HortTechnology 2:216-223
• Peet, M. M., J.M. Rippy, P.V. Nelson and G.L Catignani. 2004. Organic production of greenhouse tomatoes utilizing the bag system and soluble organic fertilizers. Acta Horticulturae 659. Proceedings of the 7th International Symposium on Protected Culture in a Mild-Winter Climate: Production, Pest Management and Global Competition. P. 707-719.
• Seo. M.H., Rhee, H.C., Lim, J.W., Kim, J.Y., Yu, C.J. and Kwon, K.C. 1994. Inter-generic compatibility and growth for grafting between Chinese cabbage and radish, RDA J. Agric. Sci. 36: 399-403
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• Walz, E. and S. Tresky. 1997. Testing solutions for control of bacterial wilt in tomatoes. OFRF Information Bulletin Spring 1997 No. 4 p. 8-9. www.ofrf.org/publications/news/ib4.PDF
• Williamson, V.M. 1998. Root-knot nematode resistance genes in tomato and their potential for future use. Ann. Rev. Plant Pathology 36:277-93.
• Yetisir, H. and Sari, N. 2003. Effect of different rootstock on plant gowth, yield and quality of watermelon. Australian J. of Exp. Agr. 43:1269-1274.
Phytotron Experiment 2006-2007:
In the spring of 2007, a controlled environment experiment was conducted at North Carolina State University’s (NCSU) Southeastern Plant Environment Laboratory. The tomato cultivars ‘Trust’, ‘German Johnson’ and ‘Maxifort’ were utilized. 'Trust' is a popular indeterminate hybrid with beefsteak-type fruit grown extensively in greenhouses. ‘German Johnson’ is an indeterminate heirloom with large pink fruit. ‘Maxifort’ is a popular hybrid used as a grafting rootstock (Solanum lycopersicum L. x Solanum habrochaites S. Knapp & D.M. Spooner., ‘Maxifort’). Six treatments were included in this study: 1) ‘Trust’ grafted onto ‘Maxifort’, 2) ‘Trust’ grafted onto ‘Trust’ (self-grafted), 3) ‘Trust’ (non-grafted), 4) ‘German Johnson’ grafted onto ‘Maxifort’, 5) ‘German Johnson’ grafted onto ‘German Johnson’ (self-grafted) and 6) ‘German Johnson’ (non-grafted).
Phytotron Seedling Production:
‘German Johnson’ seeds were sown on 22 Jan. 2007, while ‘Trust’ and ‘Maxifort’ varieties were sown on the following day. Flats were filled with a commercial potting media (Redi Earth ‘Plug and Seedling Mix’, Sun Gro Horticulture: Bellevue, WA) and topped with a thin layer of horticultural grade vermiculite. Flats were then placed in a germination chamber over a seedling heat mat (26-28°C), a 12 h light/12 h dark photoperiod (fluorescent lighting with a Photosynthetic Photon Flux Density (PPFD) of ~80 ?mol m-2s-1 during light hours), and fitted with a series of overhead fine mist water nozzles (output every 3 min for 3 s during light h only) (Shurtleff, J., 12 Sept. 2008, personal communication). When approximately 75% of the seeds had germinated (between 3-7 days), each flat was transported to a controlled environment growth chamber.
Environmental conditions of the growth chamber were maintained at day/night temperatures of 26/22°C and coordinated with a photoperiod of 12 h light/12 h dark. A combination of T-12, 1500 ma, cool-white fluorescent and 100 W incandescent lamps provided light in the chamber (PPFD readings 450-550 ?mol m-2s-1) (NCSU, 2008; Shurtleff, J., personal communication, 12 Sept. 2008). ‘Maxifort’ and ‘German Johnson’ seedlings were transplanted into propagation flats on 29 Jan. 2007; ‘Trust’ was transplanted on 2 Feb. 2007. All seedlings were watered twice per day with de-ionized water. From 5 Feb.-13 Feb. 2007 all seedlings were fertilized with a modified Steiner nutrient solution during the morning watering event followed by de-ionized water in the afternoon. The nutrient solution consisted of (in mmol): 106.23 N, 10.41 P, 111.03 K, 54.40 Ca, 12.40 Mg, 5.00 Fe, 13.19 S, 0.113 Mn, 0.24 B, 0.013 Zn, 0.005 Cu, 0.00003 Co, 0.005 Mo, 11.04 Na with a pH of 6.25.
On 14 Feb. 2007 all plants were grafted following the ‘Japanese tube-grafting’ method described in the NC Cooperative Extension Bulletin AG-675 (Rivard and Louws, 2006). Grafted plants were then placed inside a healing chamber located within the larger growth chamber. The healing chamber was an enclosed, rectangular enclosure built by stretching greenhouse grade plastic around a metal frame with mesh shelving. A cool-mist humidifier (ReliOn® Ultrasonic Humidifier, Model #FHC-502/H-0695-0) was fitted with a 90º PVC elbow and 0.3 m straight length of PVC pipe, in order to facilitate the entry of water vapor into the healing chamber below the grafted seedlings. Non-grafted treatments were transferred to a separate, cooler growth chamber, 22/18°C (day/night temperature) with all other parameters (photoperiod, etc.) the same to synchronize their growth with the recovery of the grafted treatments.
Humidity inside the healing chamber was maintained at high levels (80-90% RH) for the initial two days. Output from the humidifier was gradually decreased until the unit was turned off on the fifth day. To decrease the amount of light entering the healing chamber, black trash bags were laid on the top of the chamber for the first four days. From the second day forward,
small vents were created in the top four corners of the chamber to allow for increased airflow and facilitate the escape of hot air. Six days later, on 20 Feb. 2007, the plastic sides and roof of the healing chamber were completely removed. The grafted seedlings were left in place for an additional six days and watered delicately.
All grafted and non-grafted seedlings were transplanted into 605 cm3 pots filled with a gravel-potting media substrate mix comprised of ‘2 gravel:1 potting media (by volume)’ (Redi Earth, ‘Plug and Seedling Mix’, Sun Gro Horticulture: Bellevue, WA) on 26 Feb. 2007. From this date forward, seedlings were fertilized with a modified Steiner solution twice per day. On 31 March 2007 all plants were transplanted into 1277 cm3 pots.
Phytotron Experimental Design and Statistical Analysis:
The experimental design was a replicated 2x3 factorial with a randomized complete block design. Plants were distributed within five adjacent blocks in the growth chamber. Within each block, groups of five plants, from each of the six treatments were randomly arranged. One plant per block was selected arbitrarily to be destructively sampled each week, for a total of five weeks (22 March, 28 March, 4 April, 11 April, and 18 April). The 1st sampling date represents the 36th day after grafting (DAG) and the last sampling date, the 63 DAG. The 1st sampling date corresponded with the ‘early fruit set’ growth stage, 2nd-3rd dates with ‘1st ripe fruit’ and the 4th-5th dates with the ‘harvest period’ (Hochmuth et al, 1991).
Leaf area, leaf, stem, and fruit weight, and fruit number were sampled on a weekly basis for five weeks. Root weight, plant height, and leaf tissue for a nutrient analysis were sampled on the last harvest date only. Leaf area measurements were taken with a leaf area meter (LI-COR Model LI-3100, Biosciences, Lincoln: NE). Stems were cut at a visible graft union if present or
1.5 cm above the potting media surface. Leaf tissue samples consisted of both leaflets and petioles. Potting media was removed from plant roots by rinsing in water.
All leaf, stem, and root samples were placed in a drying oven for 24 hours at 70ºC, after which their dry weights were measured. Leaf tissue samples were ground in a Wiley Mini-Mill stainless steel grinder with a 20 mesh screen (1.0 mm) (Thomas Scientific: Swedesboro, NJ) (Campbell, 1992; Campbell and Plank, 1992) and then sent to the North Carolina Department of Agriculture and Consumer Services Agronomic Division (NCDA&CS) for nutrient analysis. Total N was determined by oxygen combustion with an elemental analyzer (NA1500; CE Elantech Instruments: Milan, Italy) (Campbell, 1992). Total P, K, Ca, Mg, S, B, Cu, Fe, Mn, Zn, and Na concentrations were determined by EPA Method 200.7 with an ICP spectrophotometer (Optima 3300 DV ICP Emission Spectrometer; Perkin Elmer Corporation: Wellesley, MA) following open-vessel HNO3 digestion in a microwave digestion system (CEM Corp., Matthews, NC) (Donohue and Aho, 1992).
Statistical analysis was carried out using a general linear model (Proc GLM) for plant growth parameters measured once at the final sampling date (i.e. height and root weight) and nutrient content of the leaf tissue (SAS Institute, Cary, NC). Multivariate analysis of variance (MANOVA) was utilized to protect against high type I errors (SAS Institute, Cary, NC). Repeated plant growth parameter measurements take over five weeks (i.e. leaf area, leaf weight, and stem weight) were transformed to their common logarithm to rectify heteroskedacity and then analyzed with a linear mixed model (Proc MIXED) (SAS Institute, Cary, NC). A non-linear mixed model (Proc NLMIXED) was employed to fit an apparent logistic growth curve for fruit weight and fruit number and also to account for small number counts (0-3) (SAS Institute, Cary, NC). Pearson correlation coefficients were used to measure associations between N leaf tissue content and random variables (Proc CORR) (SAS Institute, Cary, NC).
Experimental Protocols at the CEFS Research Station 2007-2008:
A systems comparison study was conducted at The Center for Environmental Farming Systems (CEFS)/Cherry Research Farm located in Goldsboro, NC for two consecutive years, 2007 and 2008. Plants were cultivated in two separate, 30ft x 96ft high tunnel units and two, adjacent field plots of the same size. Grafting treatments consisted of two rootstock/scion combinations, a non-grafted control, and a self-grafted control (2008 only). Grafting treatments included: 1) ‘Cherokee Purple’ scions (Solanum lycopersicum L. ‘Cherokee Purple’) grafted on ‘Maxifort’ rootstock (Solanum lycopersicum L. x Solanum habrochaites S. Knapp & D.M. Spooner., ‘Maxifort’), 2) ‘Cherokee Purple’ scions grafted on ‘Beaufort’ rootstock (Solanum lycopersicum L. x Solanum habrochaites, ‘Beaufort’, 3) ‘Cherokee Purple’ tomato plants (non-grafted) and 4) ‘Cherokee Purple’ grafted back onto itself (self-grafted) was included in 2008 only due to problems with seedling production in 2007. Each treatment listed above was subjected to three different levels of nitrogen (N) inputs: low, medium, and high. Therefore, nine treatments were included in the study in 2007 and twelve in 2008.
The experiment was arranged as a 2 x 3 x 3 (2007) or 4 (2008) factorial with a replicated split-split plot design. Main plots and subplots were randomized for each year separately. The whole plot factor was the growing system type, high tunnel or open field. The sub-plot factor was the fertilizer treatment (different levels of N), and the sub-sub plot factor was the grafting treatment. Each sub-sub plot served as an experimental unit which consisted of six plants per row in 2007 and five plants per row in 2008. Each experimental unit was replicated four times, twice in each of the high tunnels and twice in each of the corresponding fields. Guard rows were planted on the front and back end of each tunnel and field plot.
Field and High Tunnel Description:
The project area was located in the CEFS field, ‘C2’. The soil type at the project site was a Wickham, sandy loam (WhA), characterized as a deep, well-drained, and a slight to moderately acidic soil. During the fall of 2006, this field was fumigated with methyl bromide in order to manage the federally listed noxious weed ‘Tropical Spiderwort’, Commelina benghalensis L. Two high tunnels (Atlas Greenhouses Inc.: Alapaha, GA) were constructed on-site in February, 2007. The high tunnels are a snow-arch design with an inflated double polyethylene film (6 mil) roof and twin wall polycarbonate end walls. Doors built into the end walls were sized wide enough to allow the passage of a small tractor for spring tillage. Bows were spaced every 4ft and a 6ft Z-Lock drop down curtain system’ with a motorized crank was employed. Adjacent field plots were also established at this time.
Seedling Production for CEFS Experiment:
Guidelines set forth by the USDA NOP were followed during seedling production. A dilution of a soluble organic fertilizer (Omega 6N-6P-6K, Petrik Inc., Woodland, CA) was administered to all treatments once per week. Seedlings were grafted using the ‘Japanese tube-grafting’ method described in the NC Cooperative Extension Bulletin # AG-675. Approximately two weeks after grafting, all grafted and non-grafted seedlings were transplanted into larger propagation flats.
Cultural Management for CEFS Experiment:
Cultural management practices typical for each system were employed. The high tunnel system was approached as a hybrid between a greenhouse and an open field culture. Planting dates in the high tunnel system were 20 March 2007 and 18 March 2008, which were approximately one month earlier than the field system 19 April 2007 and 17 April 2008, and reflect the typical planting dates of local growers. In 2007, inner floating polypropylene fabric row covers were used to cover seedlings inside the high tunnels when evening temperatures were predicted to drop below 40°F. In 2008, the spring weather was milder and inner row covers were not employed based on the same criteria.
Plants in the high tunnel system were pinched to encourage the formation of two leaders, typical of greenhouse production using grafted transplants. These two leaders were trained to a trellis system consisting of vertical strings hanging from horizontal tension cables extending across the width of the high tunnels. The tomato vines were attached to the strings with plastic plant clips. The lower leaves were pruned up to ‘one leaf below the first fruit cluster’ and suckers were removed on a weekly basis to steer growth towards the main leaders and fruit production. In 2007, suckering was conducted throughout the season. In 2008, in an effort to decrease the amount of sun-scald damage to fruit, suckering was stopped in mid-June. The high tunnel drop down curtain system was programmed to lower the sidewall curtains when ambient air temperatures inside the tunnels reached above 65.0°F. The controller is designed to open the curtains incrementally based on the change in temperature after five minutes of idle time. At the end of each season, the high tunnels were sealed for a solarization period of approximately four weeks.
In the field system, the stake-and-weave trellis system was utilized. Leaf pruning was conducted up to the first horizontal string in the field. Plants were not pinched nor suckered, resulting in a bushier growth form compared to the high tunnel plants. Each system was irrigated on an as needed basis, evaluated twice daily. All planting rows in both systems were 13.5 ft. long and 4.5 ft. wide; plants were spaced every 22 in. Black polypropylene landscape fabric was utilized as a weed barrier in all plots. Drip tape with emitters every 12 in. and a flow rate of 19 l/hr. were used for irrigation.
Integrated Pest Management for CEFS Experiment:
Integrated pest management practices were utilized for the management of insect pests. Weekly scouting events were conducted and management decisions based on established thresholds for organic systems when available. In the early spring of 2007, the high-tunnel system experienced a high population of potato aphids, Macrosiphum euphorbia Two spot applications of insecticidal soap were carried out and followed by multiple releases of the aphid midge, Aphidoletes aphidimyza and the parasitic wasp, Aphidius ervi.
In both 2007 and 2008, applications of Bacillus thurigiensis (Bt) were applied to both the high tunnel and field system on two occasions. These sprays targeted tomato hornworms, Manduca quinquemaculata, tomato fruitworms, Helicoverpa zea, and/or armyworms Spodoptera sp.. In 2008, both the high tunnel and field system experienced high populations of stink bugs, Acrosternum hilare. However, no action was taken due as the negative effect of spraying a broad spectrum insecticide to reduce the population was judged to outweigh the benefits from the beneficial insect community present. Hand removal was the only control strategy utilized. A series of bi-culture cover crop strips were planted in succession around the perimeter of each high tunnel and field plot in Oct. 2007 and June 2008 in order to attract and sustain beneficial insects and pollinators.
Fertilizer Applications and Cover Crops for CEFS Experiment:
Three levels of total N inputs (pre-plant + post-plant applications) were evaluated each growing season. In 2007, the three N levels were 100 lbs.N/A (low), 150 lbs.N/A (medium), and 200 lbs.N/A (high). The ‘Vegetable Crop Handbook for Southeastern United States (2007)’ recommends a N application rate of 200 lbs.N/A for soils with low potassium, such as ‘C2’; this recommendation matches the 2007, high N treatment. All three fertilizer levels in 2007 provided more than adequate N as reflected in their sampled leaf concentrations. As a goal of the study was to investigate the critical level of N inputs required by a grafted tomato crop, the three N levels were lowered to 83lbs.N/A (low), 100lbs.N/A (medium), 150lbs.N/A (high) in 2008.
In 2007, a pre-plant application of 9 T/A of compost (‘Leprechaun NOP Compost’ - McGill Environmental Systems: Harrells, NC) and 91 lbs./A of feathermeal (Nutrimax ‘Super’ Natural Organic Fertilizer (12N-1P-0K), Nutrimax Inc.: Greensboro, NC) was applied to all plots, approximately two weeks before the respective system planting dates. This pre-plant application of compost and feathermeal was estimated to supply 88 lbs./A1 of crop available N. The remaining balance of N was provided to the crop over a series of post-plant, soluble fertilizer solution applications (Phytamin 801 (6N-1P-K1), California Organic Fertilizers, Inc.: Fresno, CA).
Post-plant fertilizer applications were timed to provide N to the crop at critical times during plant growth. The majority of post-plant N was supplied during the growth stages, ‘1st bloom to early harvest’ to encourage fruit production. In 2007, post-plant fertilizer was applied over five fertigation events and was dispensed to each plant by hand. In 2008, post-plant fertilizer schedule was modified to only two fertigation events and was dispensed to each plant via the drip irrigation system with the aid of a fertilizer injector set a ratio of 1:64 (Dosatron Liquid Dispenser, Model DI 16-11GPM: Clearwater, FL). Additions of K and calcium (Ca) were provided evenly across both systems based on NCDA leaf tissue analysis and soil test recommendations.
Between the 2007 and 2008 season, both systems were planted with a mixed winter cover crop. The mix consisted of hairy vetch, Vicia villosa and winter rye, Secale cereale. The cover crop was sampled just prior to mowing and soil incorporation. The growth of the cover crop in each system was very different over the course of 4-5 months. The total cover crop biomass was 43% greater in the high tunnel system (4,078 lbs./A) compared to growth in the field system (2,310 lbs./A).
The cover crop in the high tunnel system was estimated to contribute 83 lbs.N/A of crop available N compared to the field cover crop with 47 lbs.N/A for the 2008 growing season. As a result, the target amount of pre-plant N for the low fertilizer treatment was set at 83 lbs.N/A in 2008. In order to bring the field system up to the same pre-plant N input level as the high tunnel system, feathermeal was added to the field but not to the high tunnel system. Fifty-two pounds of feathermeal, with an estimated 37.0 lbs.N/A of crop available N, was supplied to the field system.
Sampling Protocols for CEFS Experiment:
Leaf tissue samples consisting of the ‘most recently mature leaves’ (MRML) were collected six or five times over the growing season in 2007 and 2008, respectively. One leaf was sampled from each plant and then combined with leaves from the same sub-plot to comprise a leaf tissue sample. All leaf tissue samples were sent to the NCDA&CS, Agronomic Division for analysis of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, Zn, and Na.
In addition to leaf tissue analysis, fruit harvests were conducted twice per week. Fruit was picked from the ‘pink to red’ stages. Fruit was sorted into marketable and non-marketable categories. Qualitative judgments relating to marketable and non-marketable fruit were based on observations from regional direct sales outlets for organic produce. Non-marketable fruit was sorted into categories including: cat-facing, blossom end rot, insect damage, fruit cracking, tomato spotted wilt virus (TSWV), sun-scald (2008 only) and ‘other’. Both the fruit number and fruit weight was recorded for each category.
Statistical Analysis for CEFS Experiment:
Statistical analysis was carried out using a multivariate analysis of variance (MANOVA) to protect against high type I errors and a linear model for repeated measures with Proc Mixed (Proc MIXED) (SAS Institute, Cary, NC). Linear hypotheses were used to test pair wise differences for fixed factors such as grafted versus non-grafted plants, and ‘Beaufort’ versus ‘Maxifort’ rootstock (‘Estimate Statements’, SAS Institute, Cary, NC). An alpha level of P?0.05 was used for all statistical tests.
Procedures for On-Farm Tests of Grafting as a Tool to Manage Major Tomato Diseases in the Southeastern US: This experiment, including materials and methods, is described in Appendix B.
Training Activities and Resource Development:
We were able to offer a number of training sessions on grafting and high tunnels throughout this project although the project did not have a fomal extension component. We also produced a number of print and web-based training resources. These activities are described in detail in the Publications/Outreach section of the report.
Controlled Environment Results (See Appendix A for Tables and Figures):
Shoot Weight, Leaf Weight, & Leaf Area. Grafted treatments (scion grafted onto ‘Maxifort’ rootstock and self-grafts combined) had higher mean values for leaf area compared to non-grafted controls (Table 1.1). Shoot weight, leaf weight, and leaf area was greater for scion grafted on ‘Maxifort’ rootstock compared to self-grafts indicating that rootstock selection can affect shoot biomass and leaf area (Table 1.1). Although both scion-rootstock graft combinations had greater stem weight, leaf weight, and leaf area compared to self-grafts and non-grafts, the grafting response was stronger for plants with ‘German Johnson’ scion compared to ‘Trust’ (Table 1.1). Interactions between scion type and grafting effect were not present.
Plant Height & Root Weight. Grafted treatments (scion grafted onto ‘Maxifort’ rootstock and self-grafts combined) had higher mean values for plant height and root weight compared to non-grafts (Table 1.1). The plant height and root weight of scion grafted onto ‘Maxifort’ rootstock and the self-grafts were not significantly different from each other indicating that plant height and root weight were a result of the physical grafting process (Table 1.1). Although both scion-rootstock graft combinations had greater plant height and root weight compared to non-grafts, the grafting response was stronger for plants with the ‘German Johnson’ scion compared to ‘Trust’ when grafted onto ‘Maxifort’ rootstock (Table 1.1). Interactions between scion type and grafting effect were not present.
Selected plant growth indicators measured over time displayed general patterns between plant growth stage and grafting effects. For example, scion grafted onto ‘Maxifort’ rootstock had
greater shoot weight on the last two out of five sampling events while leaf area was greater the last three out of five sampling events compared to the non-grafted treatments (Fig. 1.2A and Fig. 1.2B). Our results indicate that the plant growth responses to grafting can be documented 7-8 weeks after grafting.
Leaf Tissue Nutrient Content. The NCDA&CS nutrient analyses were expressed as a percentage for macro-nutrients and sodium (mg/kg * 100) while micro-nutrients were expressed as parts per million (mg/kg). Statistical analyses were carried out and presented in these same units. The mean nutrient concentration values of the leaf tissue are displayed in Table 1.2. All mean nutrient values tested (N, K, Ca, Mg, S, Fe, Mn, Zn, Na, Cu, and B) were within or above the standard adequate ranges for tomato at specific growth stages with the exception of P (Hochmuth et al., 1991). Phosphorus was slightly below the recommended range of 0.20-0.40% with a mean value of 0.16% although no symptoms of P deficiency were observed at any point during the experiment.
We compared the nutrient content (leaf tissue nutrient concentration ((% or ppm) x the dry leaf weight (g)) of the total leaf tissue rather than values for the nutrient concentration of the leaf tissue in order to account for the variability of plant growth among grafting treatments. The leaf nutrient content of each plant was calculated to attain an estimate of the total amount of accumulated nutrients in the leaf tissue on the last sampling date. The mean leaf tissue nutrient content was greater in grafted treatments (scion grafted onto ‘Maxifort’ rootstock and self-grafts) compared to non-grafts for the following nutrients: N, P, K, Mg, and B (Table 1.3). Scion grafted onto ‘Maxifort’ rootstock had greater mean leaf tissue content compared to non-grafts for N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, and B (Table 1.3). Scion grafted onto ‘Maxifort’ rootstock had greater mean leaf tissue content compared to self-grafts for: Ca, Fe, Mn, Zn, and Cu (Table 1.3). Sodium content was the only nutrient that did not show a significant difference among treatments. The grafting effect resulted in increased accumulation of selected nutrients in the leaf tissue of grafted plants compared to non-grafts. When the ‘Maxifort’ rootstock was employed in a grafting pair, increases in nutrient accumulations for all nutrients tested (*only exception Na) were greater than non-grafts. Interactions between scion type and grafting effect were not present.
Connections between plant growth, fruit yield and nutrient availability have been well established among non-grafted plants (Epstein and Bloom, 2005; Marschner, 2008; Mengel and Kirkby, 2001). Establishing a link between N uptake and plant growth in grafted tomatoes was approached by conducting a Pearson correlation analysis. The N content of the leaf tissue was positively correlated with shoot weight (87%), leaf area (81%), plant height (76%), and root weight (75%) reaffirming the close relationship between N uptake and plant growth (P<0.0001, data not shown). These results indicate that N content in the leaf tissue resulted in greater shoot growth in grafted plants compared to non-grafted (Fig. 1.2).
Both ‘Trust’ and ‘German Johnson’ scion grafted onto ‘Maxifort’ rootstock had similar responses to grafting in terms of nutrient accumulation in the leaf tissue. The nutrient content values for N, P, K, Mg, S, Mn, and Zn were statistically similar between scion selections (Table 1.4). Greater values of Ca, Fe, and Cu were present for the scion variety ‘Trust’ compared to ‘German Johnson’ when grafted on ‘Maxifort’ rootstock (Table 1.4). Our results suggest that the scion selection influences the uptake of selected nutrients but that these effects are the exception rather than the norm. Interactions between scion type and grafting effect were not present.
Fruit Yield. Logistic growth curves were fitted to each grafting treatment over time with a nonlinear model; these growth curves suggested that fruiting on the grafted plants was delayed.
Unfortunately, the asymptote occurred beyond the region of collected data within the time frame of this experiment and therefore the analysis proved not to be a reliable estimate of fruit production over time. At the conclusion of the study, the non-grafted treatments produced a greater number of fruit compared to the grafted treatments (data not shown, P=0.0019).
N Leaf Content and Root Weight. The relationship between leaf tissue N content and root weight was examined to investigate whether the increase in root weight associated with grafting was linked to an increase in leaf tissue N content. The ‘leaf tissue N content : root weight’ ratio was not different among grafted and non-grafted treatments (data not shown, P=0.3668) suggesting that the increase in root growth in grafted plants may be responsible for the proportionally higher levels of N accumulation in the shoot. The scion type did affect the ‘leaf tissue N content : root weight’ ratio with the ‘Trust-Maxifort’ grafts having a higher ratio of 13:1 compared to 11:1 for the ‘German Johnson-Maxifort’ grafts. Though there was no significant difference between leaf tissue N content among the two cultivars (Table 1.4), differences in shoot:root ratios (‘Trust’ greater than ‘German Johnson’) (Table 1.1) can explain this phenomenon.
Overall our study confirms that both increased plant productivity and greater leaf tissue nutrient content is achieved by grafting tomatoes. Plant response to the physical act of grafting appear to be the most important factor for stimulating plant growth and nutrient uptake, however, utilizing the ‘Maxifort’ rootstock expanded the range and level of grafting effects. Scion selection played a very minor role in treatment effects and scion-rootstock interactions were not present. The positive relationship between the accumulation of nutrients in the leaf tissue and shoot growth among grafted plants suggests that grafted tomatoes can achieve greater plant productivity at the same nutrient input levels compared to non-grafted plants.
Research Station (CEFS) Results:
In both 2007 and 2008, the high tunnel system produced greater total fruit yields (weight and number of fruit) and hit peak production three weeks earlier compared to the field system (Fig. 1.4 & 1.5). In both 2007 and 2008, the high tunnel system had a higher incidence of fruit with blossom end rot and cat-facing but lower incidence of TSWV and insect damage compared to the field system (Fig. 1.6 & 1.7). The mean leaf tissue concentrations of N, P, K, Ca, Mg, and Fe were higher in the high tunnel system in 2007. The same nutrients listed above were lower in the high tunnel system compared to the field system in 2008. These opposing trends were likely related to the differences of incorporated winter cover crop biomass preceding the spring tomato crop planting (see methods section for more details). The mean leaf tissue concentrations of Mn, Cu, B, and Na were lower in the high tunnel system compared to the field system across both years.
In 2007 and 2008, both the Maxifort-CP grafts and the Beaufort-CP grafts had greater total and marketable fruit yields compared to non-grafted plants (Fig. 1.8 & 1.9). These yields were attained in a low disease pressure environment. Maxifort-CP grafts and the Beaufort-CP grafts also had higher rates of culled fruit, cracked fruit, and insect-damaged fruit compared to non-grafted plants for both seasons. The mean leaf tissue concentrations for grafted plants were greater for N, P, K, Mn, Cu, Zn, and B but lower for Mg and Na compared to non-grafted plants across both years. Self-grafted (2008 only) were similar to non-grafted plants for all leaf tissue nutrient concentrations results. ‘Cherokee Purple’ scion grafted on ‘Maxifort’ rootstock had greater mean leaf tissue nutrient concentrations for P, S, Cu and Zn compared to those grafted on ‘Beaufort’ rootstock across both years, the opposite was true for B and Mg suggesting that rootstock selection can influence nutrient accumulation in the leaf tissue.
Nitrogen Input Level Effects.
The mean leaf tissue N concentration never fell below standard optimum N ranges at any of the N input levels evaluated over the course of the two year study (83-200lbs.N/A). In 2008, both the high and medium N input levels (150lbs.N/A and 100 lbs.N/A, respectively) produced greater total harvest yields compared to the low N level (83lbs.N/A) (Fig. 1.10). A positive correlation between mean leaf tissue N concentrations and total fruit yield (>70.4%) was present in 2008 indicating a strong relationship between % N concentration and grafting onto hybrid rootstocks that in turn boosts fruit yield (Fig. 1.11 & 1.12).
In conclusion, maximum fruit yield were achieved with the combination of the high tunnel system and the ‘Cherokee Purple-Maxifort’ grafts indicating that when specific scion-rootstock combinations are paired with the more controlled environment fruit yields can be maximized (Fig. 1.13). Grafted plants attained higher yields compared to non-grafts even in a low disease pressure environment suggesting that higher seedling costs may be offset by greater yields even when soil borne disease pressure is absent. Grafting resulted in greater nutrient accumulation in the leaf tissue for the majority of essential nutrients. Although the system and fertilizer level effects on leaf tissue concentration were variable across the two study years, grafting effects were consistent, indicating that grafting on hybrid rootstock had the strongest influence on nutrient accumulation in the leaf tissue.
On Farm Results: Results from On-Farm Tests of Grafting as a Tool to Manage Major Tomato Diseases in the Southeastern US are described in Appendix B.
Educational & Outreach Activities
Publications, presentations and posters are listed below.
M.S. Thesis: Grafted Tomato Performance in Organic Production Systems: Nutrient Uptake, Plant Growth and Yield by Suzanne O’Connell (12/08) <http://www.lib.ncsu.edu/theses/available/etd-11072008-152636/>.
M.S. Thesis: Rivard, Cary L. 2007. Grafting Tomato to Manage Soilborne Diseases and Improve Yield in Organic Production Systems. North Carolina State University., Raleigh, NC.
Presentations (Presenter) at Grower Meetings:
National Association of County Agriculture Agents Conference, 'SARE-funded Research at CEFS: Grafting Heirloom Tomatoes for Disease Resistance in Intensive Farming Systems'. Presenters: S. O'Connell, C. Rivard, S. Hartmann (participating farmer). Greensboro, NC. July 15, 2008. Pre-registration ~75.
Growing Small Farms: Enhancing Sustainability Workshops 'Heirloom Tomato Grafting Workshop'. Presenters: S. O'Connell, M. M. Peet, C. Rivard, A. Hitt (participating farmer). Pittsboro, NC. Nov. 12, 2008. ~ 50 attendees. Presentation online at: <http://www.ces.ncsu.edu/chatham/ag/SustAg/2008tomatografting.html>
Seasons of Sustainable Agriculture Series 'High Tunnel Workshop and Tour'. O'Berry Center, Goldsboro, NC. 'Nutrient Management'. Presenter: S. O’Connell. Feb. 17, 2008. ~60 attendees.
Center for Environmental Farming Systems (CEFS) Goldsboro, NC. February 17, 2009. Seasons of Sustainability Agriculture Workshop Series on High Tunnels. Presentations on “Organic Nutrient Management (O'Connell)", "Disease Management & Microclimate Modification (Rivard)”
"Marketing Options & Crop Selection (Peet)". . ~ 50 Attendees. <http://www.cefs.ncsu.edu/calendar2009.htm#hightunnel>
‘Heirloom Greenhouse Tomatoes: Grafting, Tunnels, and Other Options’ (Mary Peet) 2008 Greenhouse Tomato Short Course, Raymond, Mississippi, March 4, 2008. About 100 attendees
'High Tunnels: Selection, Design, Economics and Management' and 'NC High Tunnel and Grafting Experiences: 2005-2008' Greenhouse Tomato Short Course, Raymond, Mississippi, March 10-11, 2009. The .pdf versions of these talks are available at: http://greenhousetomatosc.com/.
http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/ under grafting and High Tunnel topics
Demonstrations of grafting to individual growers (presenter):
Roberts, Mary. Windcrest Organics. Monroe, NC. 8/12/08. (O'Connell) <www.windcrestorganics.com> *now selling organic grafted tomato transplants 1/08.
Hartmann, Stefan. Black River Organic Farm. Ivanhoe, NC. 3/08. (O'Connell and Rivard) http://www.blackriverorganicfarm.com/
Barham Farms Greenhouses. Zebulon, NC. 11/07. (O'Connell)
Academic Grafting Demonstrations:
Rivard, Phytotron, March 12, 2009, HS543 15 students and two observers.
O'Connell, March 2007 for HS543 and November 2007 for HS431. 30 students total, including undergraduate and graduate students.
Talks to students:
Cary Rivard Grafting, HS543 March 2007 and Feb. 26, 2009, 30 students total.
Peet, M. ‘Grafting Heirloom tomatoes for Field and High Tunnel Production Using Organic Practices’ Special seminar at Controlled Environment Agriculture Center, University of Arizona, Tucson, AZ. Oct. 28 2008. About 40 attendees
Grafting Workshop for Georgia Extension and Class. Hosts Julia Gaskin and Robert Tate. 1:00-4:00 pm March 3, 2009, Athens, Georgia. Talks and demonstrations by Cary Rivard.
Popular Press articles about NCSU grafting research and that of NCSU cooperators:
Grafting Heirloom Tomatoes. Feature on Cary Rivard's project GS05-046 and LS06-193 p. 5 in Spring 2008 issue of Common Ground. SR-SARE.
Grafting Tomato Seedlings Could Enhance Field Production. December 2008. The Tomato Magazine. p. 4-5. Article based on Ohio State led grafting project.
Multistate tomato grafting project has potential for growers. The Vegetable Growers News Vol 42(9) September 2008. p. 1 & 16. article by Matt Milkovich on Ohio project with quote from Louws.
Pennsylvania Grower Achieves 20 Percent Gains with Grafting. The Tomato Magazine June 2009 p. 4-5
Abstracts presented at Scientific meetings:
High Tunnels and Grafting For Disease Management In Organic Tomato Production. 2008. (Cary Rivard) Rivard CL, Louws FJ, Peet MM, and O’Connell, S. Phytopathology 98:S133-S133 American Phytopathological Society Centennial Meeting 2008 Minneapolis, Minnesota July 26-30.
Nutrient Uptake Efficiency and Plant Growth Indicators of Grafted Tomatoes. 2008. (Suzanne O'Connell). O'Connell, S. and Peet M.M. HortScience 43:3. American Society of Horticultural Science Southern Region 68TH Annual Meeting. Dallas, Texas. February 2-4, 2008.
Improving performance of organic heirloom tomatoes using high tunnels and grafting. 2008. (Mary Peet) Mary Peet, Suzanne O'Connell, Cary Rivard, Frank Louws. ISHS Symposium on Tomato in the Tropics. Villa de Leyva, Colombia. September 9-12. 2008.(poster)
‘Grafting Rootstocks onto Heirloom and Locally Adapted Tomato Selections to Confer Resistance to Soil Borne Diseases and Increase Nutrient Uptake for Market Gardeners’ New American Farm Conference. (Mary Peet) Mary Peet, Suzanne O’Connell, Frank Louws, Cary Rivard, and Chris Harlow. Advancing the Frontier of Sustainable Agriculture. Kansas City, Missouri. March 25-27, 2008. Poster available at: http://www.sare.org/2008Conference/posters.htm
‘Nutrient Uptake Efficiency and Plant Growth Indicators of Grafted Tomatoes (Suzanne O'Connell*) Suzanne O'Connell and Mary M. Peet 68th Annual Meeting Southern Region American Society for Horticultural Science. Dallas, TX. Feb. 2-4 2008. *Winner of Southern Region Graduate Student Poster Competition.
‘The Performance Of Grafted Heirloom Tomatoes In Organic Production Systems: High Tunnels And The Open Field’ (Suzanne O’Connell**) O’Connell, S, Peet, M. Harlow, C. Louws, F. and C. Rivard. American Society for Horticultural Science Annual Conference Orlando, FL July 21-24 2008. **Winner of National Graduate Student Poster Competition. O'Connell selected for student travel award.
Peet, M. O’Connell, S., Rivard, C., Louws, F. and C. Harlow. 2008. Improving Performance of Organic Heirloom Tomatoes Using High tunnels and Grafting. ISHS Symposium on Tomato in the Tropics. Villa de Leyva, Colombia. September 9-12. 2008. 300 conference attendees.
Peet, M., Rivard, C., O’Connell, S., Louws, F. and C. Harlow. 2008. Use of High Tunnels and Grafting for Organic Production of Heirloom Tomatoes in North Carolina. ISHS International Workshop on greenhouse Environmental Control and Crop Production in Semi-Arid Regions. Tucson, Arizona. October 20-24, 2008
Grafting to Manage Soilborne Diseases in Heirloom Tomato Production. Cary L. Rivard and Frank J. Louws. HortScience 43:2104-2111. This article was the #5 download in December 2008, the month it appeared.
Grafting for Disease Resistance in Heirloom Tomatoes. Rivard, C. and Louws, F. 2006. NC Cooperative Extension Service AG-675
This project generated interest in grafted tomatoes, especially among small and organic growers and those producing heirlooms for direct markets. Eighty percent of May 15, 2008 CEFS workshop attendees planned to use 2-3 ideas from the presentations within the next year. In 2009, three growers that attended grafting workshops began producing their own seedlings and two began offering grafted tomato seedlings for sale. Informal data collection at conferences, farm tours, etc. indicates that many small growers across the country are experimenting with grafted seedling production using materials and information generated by our research group for guidance. More than 4 extension professionals located in NC, PA, MI and GA have utilized group research materials and data to conduct grafting workshops for local growers and other interested parties.
Steve Groff, a Pennsylvania grower widely recognized for his innovative farming practices, environmentally friendly farming and leadership in the sustainable farming community is a good example of how our grafting research has already had a 'real world' impact. Steve gave an address on his results with grafting 'My Experience Grafting Tomatoes' at the 2009 Mid-Atlantic Fruit and Vegetable Conference in Hershey, Pa and has hosted numerous on-farm tours. As described in his farm website: www.cedarmeadowsfarm.com, during the period Nove 2008-Sept. 2009 he has scheduled 18 talks, including 3 international talks. Of these talks, 5 included high tunnels or grafted tomatoes. His grafting experiences were also described in the June 2009 issue of the Tomato Magazine p. 4-5 'Pennsylvania Growers Achieves 20 Percent Gains with Grafting'. In this article, Steve says "I feel grafting has a viable place in commercial production, especially where tomatoes are grown continuously or soil disease pressure is high. In the 2008 growing season, using the grafted and control transplants we provided, he realized 9.4 additional tons per acrea of marketable fruit, a 20% increase. In 2008, the grafted transplants maintained higher 20% higher productivity despite the presence of Verticillium wilt in the field. Graft plans exceeded controls in terms of both fruit size and number. differences were most pronounced at the end of the season.
There were also three tomato spacings in our research at Steve's farm. Grafted plants produced more than non-grafted at all spacings, but the greatest potential for grafted plants was seen at the widest spacing (36") where grafted plants produced more per acre than the ungrafted controls at the 18" spacing. Thus costs could be reduced by planting at lower densities. Looking just at returns from the typical 18" spacing, gross income from the grafted transplants was 17% higher than from the controls. Overall, at $12/box, 9,024 additional gross income (or $1.88/plant) was seen in the grafted tomatoes. In 2009, he plans on increasing the number of grafted tomatoes on his farm from 500 to 8,000. Steve concluded that "The results of this trial show that grafting with vigorous rootstock is effect at increasing fruit yield through increased fruit size and number and that grafted plants maintain crop productivity under sever disease pressure from Verticillium wilt."
As another example of impact is the amount that our work has already been cited or mentioned in both the scientific and popular press. In the June 2009 issue of the Tomato Magazine, an article on 'Year-Round Heirlooms' p. 6-11 cites work by Rivard and Louws on bacterial wilt resistance imparted by the rootstock. The Rivard and Louws article which appeared in the December 2008 issue of HortScience was also #5 in the list of articles read in December. As another example of the overall interest in grafting research, in November 2008, #2 and #5 of the most read HortScience articles were about grafting. While not published by our immediate group, we are collaborating with individual authors of both articles in current grant proposals.
Impact of results of On-Farm Tests of Grafting as a Tool to Manage Major Tomato Diseases in the Southeastern US: This experiment, including it's impact, is described in Appendix B
In the future, we expect that many more researchers will be involved in both grafting and high tunnel technology, and have also applied for SCRI funding to extend the results of this project.
On-farm data from Steve Groff's farm in Lancaster, PA, discussed in the Impact section suggest about a 20% increase in profits is possible using grafted plants. In areas where tomatoes otherwise cannot be grown because of soilborne diseases such as bacterial wilt, the potential economic benefit would be even higher. One of our on-farm cooperators, for example, had not previously been able to grow tomatoes on his organic farm for a number of years.
Anecdotally, all the on-farm cooperators felt that grafting was a valuable technology, and would have purchased additional grafted transplants had they been available. By adjusting spacing and double-heading, potentially the cost of grafted seedling available commercially could be comparable to non-grafted because few transplants would be required per acre. However, additional research will be necessary for verification of this proposition.
We are cooperating on another project with Ohio State University to collect and analyze additional economic data, and this will be reported on at a later time.
This has been discussed in the sections on impacts and economics. Specifically Steve Groff, a Pennsylvania grower, used 500 grafted transplants we provided in 2008 and was so pleased with the outcome that he is planting 5000 grafted transplants in 2009. A local Pa. propagator attended the grafting workshop in Pittsboro, NC we conducted November 12, 2008 to obtain training in our procedures. In addition a producer of organic transplants in western NC came to Raleigh for an individualized demonstration of grafting techniques and also attended the Pittsboro workshop. She now produces grafted transplants for sale: http://www.windcrestorganics.com/Transplants/GraftedHeirloomTomatoes.html.
Dozens of growers have contacted us requesting grafted tomato transplants either for trials or production. However, we were only able to provide transplants for those growers participating in the studies described in this report.
A number of growers have successfully produced their own transplants either after attending one of our workshop or after reading some of our information. For example, Brandon Fahrmeier of Fahrmeier Farms in Lexington, MO http://www.fahrmeierfarms.com/ found our grafting instructions http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/pdf/Grafting.Rivard.pdf online in 2007 and successfully produced transplants for their field and 2 acre Haygrove high tunnel operation. Although their grafting success rate was not as high as we see in the phytotron, they were very pleased with the results, and planned to expand the number of grafted tomato seeding used in the 2008 production season. I was not aware of their interest in or use of grafting until visiting their greenhouse on a SARE tour at the March 2008 national SARE conference.
Areas needing additional study
The expansion of commercial sources of grafted tomato transplants in the U.S. is critical now that the commercial viability of grafting has been demonstrated. Additionally, the development of grafting rootstocks for different growing systems, increased nutrient uptake, greater fruit yield, and disease management issues will maximize the benefits conferred by farmers incorporating this technology.
Some specific areas where research could have an immediate impact are modifying training systems for grafted tomatoes to reduce the number of grafted transplants that would need to be purchased. We have preliminary data from on-farm trials indicating that both double-heading (allowing two shoots to grow instead of a single leader) and wider spacings allow equal production per unit area with few grafted transplants. Management of the grafted tomato plants in terms of pruning of suckers, time of planting, and length of time in production may be different.
In addition, we utilized only a few scions and rootstocks in our research. Rootstock-scion interactions should receive further study. We had hypothesized than an heirloom cultivar would have lower vigor and benefit proportionately more from a vigorous rootstock, but an insufficient number of scions were tested to establish whether or not this was the case.
Screening rootstocks for disease resistance should also be a high priority. Although were were able to identify rootstocks with resistance to a number of very serious soilborne diseases in the Southern Region, in the case where multiple soilborne diseases are present, no one rootstock may have all the required resistances. We did see some evidence that vigorous rootstocks might allow the grafted plant to continue to grow and produce even though plants showed some evidence of disease. It would also be interesting to evaluate the ability of resistant rootstocks to serve as a rotational crop in the situation where disease is present in the soil, but the grower still needs to produce a tomato crop.
Recommendations for further research based on the data from On-Farm Tests of Grafting as a Tool to Manage Major Tomato Diseases in the Southeastern US are discussed in Appendix B