Grafting with inter-specific hybrid rootstock is effective for tomato (Solanum lycopersicum) growers looking to reduce soilborne disease organically and increase fruit yield in the Southeastern US. However, production with grafted tomatoes has not been tested in the Great Plains region of the US. Small-acreage growers would like to produce grafted plants themselves, but many have difficulty with propagation due to water stress in the scion post-grafting and/or high temperatures within healing chambers. Growers may be able to reduce water stress post-grafting by removing the upper portion of the shoot to reduce leaf surface area, but no data exist on the potential effects of this practice on mature plant yield. Five high tunnel and one open-field study were conducted in 2011 and 2012 to investigate yield effects related to the use of two rootstocks and shoot removal during the grafting procedure. Grafting significantly increased fruit yield in five of the six trials (P<0.05). The average yield increases by Maxifort and ‘Trooper Lite’ rootstocks were 53% and 51%, respectively, across all trials. In some trials shoot removal during the grafting process reduced yield and could depend upon rootstock vigor. Another series of experiments were performed testing the efficacy of shoot removal for graft survival during the healing period prior to field planting. We also determined environmental conditions by monitoring temperature and relative humidity (RH) in all healing chambers. Five healing chambers designs were evaluated, and no significant effects of treatment design were observed upon grafted seedling survival. Plants grafted with no chamber had success rates of 81% to 91%. Additionally, three grafting leaf removal techniques were studied, and a partial leaf removal method had significantly higher success rates as compared to fully foliated and defoliated plants (P<0.05). Partial leaf removal may be recommended as a way to reduce water stress in the plant, and could potentially be a way to simplify the grafting process for small-scale producers. Environmental monitoring within the healing chambers showed the various microclimates of the chamber designs. Interestingly shade cloth increased RH humidity slightly while plastic chambers with no humidifier held very high RH (>85%).
The domestication and cultivation of food sources gave rise to human settlement and ultimately modern civilization. Humans have sought methods to improve crop success for several millennia. Grafting, an ancient technique of unknown specific historical origin, was developed to improve production in woody plants by means of growing the vascular systems of two related species. Ultimately, grafting improves yield quality and volume via the union of desired qualities from two initially separate plant bodies. Despite the application of this technique originating with fruit trees, grafting may be employed with vegetable – specifically solanaceous and cucurbitaceous – crops in order to improve yield and combat soilborne pathogens. Furthermore, the resurgence in growers’ interest in organic cultivation practices and mandated phaseout of some soil fumigants have made vegetable grafting a major topic of interest in the horticultural community throughout the past decade (Davis et al, 2009; Kubota et al., 2008, Louws et al., 2010).
Although grafting is useful for managing soilborne diseases, many of them are not common at high frequencies for Midwestern growers, as they are not as established in the region compared to other areas of the United States due to cropping history. Therefore, a major point of interest in the case for herbaceous grafting is that of increasing crop productivity. Specifically, yields are increased in grafted watermelon and cucumber (Pavlou, Vakalounaki, and Ligoxigakis, 2002; Upstone, 1968), Tomato grafting usually leads to increased fruit yield via larger fruit size (Pogonyi at al., 2005; Augustin, Graf, and Laun, 2002). This increase in output vigor is linked to heightened rootstock growth, thereby affecting water uptake and nutrient content (Leonardi and Giuffrida, 2006; Ruiz, Belkbir, and Romero, 1996; Fernandez-Garcia et al., 2002).
Many organic growers are implementing the use of high tunnels as a way to reduce foliar disease and extend the growing season (Carey et al., 2009). However, managing soilborne diseases can be very difficult in these systems as crop rotation intervals are often reduced as a way to sustain profitability. Research suggests that grafting is effective at reducing the incidence and/or severity of soilborne diseases such as root-knot nematodes (Rivard et al., 2010b), southern blight (Rivard et al., 2010b), fusarium wilt (Rivard and Louws, 2008), and verticillum wilt (Groff, 2009). In the Midwest, organic tomato growers encounter verticillium wilt, fusarium wilt, and root-knot nematodes regularly, and southern blight incidence can vary, depending on summer growing conditions and soil type. Furthermore, many organic growers in Kansas and throughout the US are utilizing specialty cultivars such as heirlooms in order to cater to local niche markets. These varieties are highly susceptible to soilborne as well as foliar diseases and the implementation of high tunnels and grafting together can be particularly useful as an Integrated Pest Management (IPM) approach to disease management for heirloom tomato production. Available research suggests that grafting will be beneficial for tomato growers in the US (Kubota et al., 2008) and particularly for organic growers who are utilizing heirloom cultivars to capture specialty markets (Rivard et al., 2010a).
Although grafting may be very useful for tomato growers in the Midwest, there is virtually no market availability of grafted plants propagated in the US, and more than 30 million grafted plants are imported from specialty nurseries in Canada for the US (Kubota et al., 2008). Even though a current and future market for grafted tomato plants exists, very few (if any) propagators in the United States have started grafting at a commercial scale for fruit production. This market gap has resulted in a large increase in interest recently in regards to tomato grafting for the US. However, still little information is available in the US in regards to grafted tomato propagation.
This project seeks to conduct a research and extension program that will provide support and answer relevant questions for this clientele as the US propagation industry continues to progress in this area. Grafted propagation techniques have not been explored in a comprehensive way and there is a strong need to determine healing chamber management and post-grafting environment manipulation in a systematic way. Furthermore, there is a significant need to demonstrate propagation methods in regards to economic optimization. A recent publication showed that grafting can add $0.46 to $0.74 per plant depending on heating costs and other factors (Rivard et al., 2010c). In this case, the growers were utilizing the tube-grafting technique (Lee, 1994; Rivard and Louws, 2006), and this technique is commonly used in commercial production systems worldwide (Lee, 1994; Lee, 2003). Once the plants are grafted, they are placed into a “healing chamber” which is a small tent that allow for the proper environmental manipulation to promote graft union (Rivard and Louws, 2006).
Although growers can perform their own grafting, managing the grafted plants can be difficult (Groff, 2009; O’Connell et al., 2009). Grafted plants are usually placed inside “healing chambers” to maintain high humidity and reduce light intensity (Rivard et al., 2010c). Plastic healing chambers built inside greenhouses can overheat, leading to plant wilting and death. Healing chambers also add to the cost of producing a grafted transplant, as they require additional materials and labor (Rivard et al., 2010c). Reducing leaf area could reduce water stress and reduce the need for humidity management. This method is commonly used with ornamental and woody plants (Christopher, 1954; Harris, 2003). Reducing leaf area via elimination of scion shoots, reliance on the healing chamber can be greatly reduced or eliminated altogether. However, there is little information available as to whether this process scion shoot removal will affect tomato yield and fruit quality in a production setting in addition to healing chamber design/modifications. Therefore, there were five primary overall objectives for this research: (i) to determine the efficacy of two rootstock cultivars at increasing tomato fruit yield in high tunnels; (ii) to test the effect of scion shoot removal upon mature plant yield and biomass; (iii) to determine how healing chamber design (supplemental humidity and covering) affects graft survival; (iv) to determine how healing chamber design affects the healing chamber environment; (v) and to determine how scion shoot removal affects graft survival in different healing chambers.
This work elaborates upon two experiments designed to analyze different facets and effects of tomato grafting. The first experiment aimed to determine the efficacy of two rootstock cultivars at increasing tomato fruit yield in high tunnels as well as test the effect of scion shoot removal upon mature plant yield and growth. The second experiment focused upon the propagation of grafted plants by determining how healing chamber design (supplemental humidity and covering) affects graft survival; determining how healing chamber design affects the healing chamber environment; and determining how scion shoot removal affects graft survival in different healing chambers. Overall, the goal of this research is to investigate and streamline the tomato grafting in order to enhance the effectiveness and utilization of this technology. We were successful at reaching all of our major performance targets by completing the proposed field (high tunnel) studies in addition to the greenhouse work proposed. We were also successful at completing the objectives outlined focused on outreach and dissemination. We coordinated and delivered a half-day workshop focused on tomato grafting at the Olathe Horticulture Research and Extension Center. The workshop was well-attended by approximately 30 growers. Evaluations are provided below. We were also successful at producing several short informational videos discussing the propagation of grafted tomatoes as well as the research supported by this grant.
2011/2012 Field Trial Materials and Methods
All grafted and nongrafted transplants were produced at the Throckmorton Plant Sciences Center at Kansas State University (Manhattan, KS; http://www.hfrr.ksu.edu/p.aspx?tabid=38). Scion and nongrafted cultivars were grown from commercially available ‘BHN 589’ seed (Siegers Seed Company, Holland, MI) and ‘Cherokee Purple’ (Johnny’s Selected Seeds; Winslow, ME). ‘BHN 589’ is a determinate variety popular with high tunnel growers with fusariam wilt, verticillium wilt (race 1), and root-knot nematodes. ‘Cherokee Purple’ is a commonly grown indeterminate heirloom variety with no known resistance to soilborne pathogens. Commercially available rootstock cultivars Maxifort (De Ruiter Seeds, Bergschenhoek, The Netherlands) and ‘Trooper Lite’ (Seedway, Hall, NY) were selected as rootstock for the grafted treatments. Maxifort carries resistance against fusarium wilt (races 1 and 2), root-knot nematodes, tobacco mosaic virus, and verticillium wilt (race 1). ‘Trooper Lite’ confers resistance to: fusarium crown/root rot, fusarium wilt (race 2), tomato mosaic Virus, root-knot nematodes and corky root.
In all trials a nongrafted control treatment was included as a standard comparison. All treatments were grafted via the Japanese tube grafting technique (Rivard et al., 2010c). Rootstock and scion seedling stems were cut and held together with a silicon clip. In the case of the shoot removal treatments (SR), shoot biomass (5-10 mm above scion cotyledons) was removed during the grafting procedure. All grafted seedlings were subsequently placed inside a 0.91 x 1.22 m x 0.60 m healing chamber with a plastic cover, 55% shade cloth, and a supplemental cool-mist humidifier as described in Rivard et al. (2010a). Following graft union formation, approximately 10 days after grafting, all tomato seedlings were removed from the healing chamber and grown in the greenhouse for approximately 14 days prior to field transplanting.
A total of six experiments were conducted at four sites in 2011 and 2012. All six trials contained five identical treatments and were planted in a randomized complete block design with four replications. Five trials were located in high tunnels and treatments included: nongrafted ‘BHN 589’, ‘BHN 589’ grafted onto Maxifort using standard methods, ‘BHN 589’ grafted onto Maxifort rootstock with the shoot removal technique (SR, described above), ‘BHN 589’ grafted onto ‘Trooper Lite’ rootstock and, ‘BHN 589’ grafted onto ‘Trooper Lite’ rootstock with the shoot removal technique (SR). The Reno County trial had the same rootstock/grafting method treatments, but utilized an heirloom scion, ‘Cherokee Purple’, and was grown in the open-field.
All tomato fruit were harvested and graded as marketable or non-marketable based upon on-farm standards including presence of fruit diseases, blossom end rot, and/or pest damage. Fruit weight and number were recorded for each grade for each plot. All fruit larger than 5 cm were harvested at the end of each growing season and included in total yield. Shoot biomass was collected from one centrally-located plant per plot at the end of the trials. Samples were dried at 70°C for at least 96 hours and weighed to determine the effect of rootstock and scion shoot removal on plant growth.
High tunnel trials were conducted in 2011 and 2012 at the K-State Olathe Horticulture Research and Extension Center (OHREC) located in Johnson County, KS (38.884347 N, 94.993426 W). The soil type at this location consists of Chase silt loam (pH= 6.3). This research trial was conducted within the central two rows of a three season, single-bay high tunnel (Haygrove, Inc.; Ledbury, United Kingdom) measuring at 7.3m x 61m. Two replications were planted within each of the two 30-m rows. ‘BHN 589’ was used as a nongrafted control and as scion for the grafted treatments. Each plot contained seven plants in 2011 and six plants in 2012. In 2011 plots measured at 4.88 m2, and in 2012 plots measured at 4.18m2. Each of the five treatments was randomly assigned to 3.8 m plots within each of the four blocks. Cultural methods were consistent with commercial organic tomato production. In-row plants spacings were at 46 cm and rows were 1.5 m apart. In 2011 plots measured at 4.88 m2, and in 2012 plots measured at 4.18m2. Pelletized organic poultry manure (Chickity Doo-Doo™, Lake Mills, WI) was applied at a rate of 114.5 kg N per hectare at planting and water was applied throughout the growing season by drip irrigation. Weeds were suppressed via woven fabric mulch and plastic mulch in 2011 and 2012, respectively, and plants were trained in to a vertical stake-and-weave trellis system.
The Olathe Horticultural Research and Extension Centertrials were planted on 12 May in 2011 and 23 April in 2012. In 2011, harvests occurred on 13, 19, and 26 July; 2, 9, 16, 23, and 30 August; 6, 13, 20, and 27 September; and 4 and 11 October. In 2012, harvest dates were on 19 and 26 June; 3, 10, 12, 16, 24 and 30 July; 7, 14, 21 and 28 August; 4, 12, 18 and 29 September; and 5 October.
Trials were conducted in 2011 and 2012 at a commercial farm located in Johnson County, KS (38.76473 N, 95.008022 W) at Gieringer’s Orchard (http://www.gieringersorchard.com). The soil type in this location consisted of Sibleyville loam (pH=7.7). The trial was conducted in a (9.1m x 29.3m) gothic arch high tunnel annually planted with tomatoes. This trial was managed conventionally, with a fungicide application administered after transplanting and conventional insecticides applied as needed. ‘BHN 589’ was used as a nongrafted control and as scion for the grafted treatments. The trial occupied the inner four rows of the high tunnel, which had eight rows total. The four replications were planted within four 15-m rows with 1 replication per row. Each of the five treatments was randomly assigned to 2.4-m length plots within each of the four blocks. Every plot contained five plants with in-row spacings at 61 cm apart and row spacings at 1.1 m. Water was applied through drip irrigation beneath fabric mulch, which suppressed weeds. Tomato plants were trained into a modified stake-and-weave trellis system with 2 cm plastic plant clips (Hydro-gardens, Colorado Springs, CO) used to hold vines to the string trellis. All treatments were transplanted into the high tunnel on 25 April in 2011 and 21 March in 2012. Fruit were harvested on 13, 16, 19, and 26 July; 2, 9, 16, 23, and 30 August; 6, 13, 20, and 27 September; and 4, 11, and 18 October 2011. In 2012, harvests occurred on 11, 19, and 26 June; 3, 10, 17, 24 and 30 July; 7, 14, 21 and 28 August; as well as 4 and 7 September.
A trial was conducted in 2012 at the Gibbs Road farm location of Cultivate Kansas City, a non-for-profit urban farming advocacy organization (http://www.cultivatekc.org) in Wyandotte County, KS (39.057955 N, 94.678209 W). The soil type in this location is composed of a mixture of both Lagoda silt loam and Marshall silt loam (pH=6.2). The trial was conducted in a 7.3m x 2.9 m homemade quonset-style high tunnel that undergoes seasonal crop rotations. ‘BHN 589’ was used as a nongrafted control and as scion for the grafted treatments, and this trial was managed organically.
The four replications were located in the two central, 27.4 m rows. Each plot contained five plants with in-row spacings at 45.7 cm apart and row spacings at 1.52 m. Pelletized organic poultry manure (Chickity Doo-Doo™, Lake Mills, WI) was applied at a rate of 143.1 kg N per hectare at planting and water was applied throughout the growing season by drip irrigation. Straw mulch was applied and tomato vines were trained in to a stake-and-weave system. All treatments were transplanted into the high tunnel on 28 March. Fruit harvests occurred on 15, 18, 25, and 28 June; 2, 3, 6, 9, 13, 16, 23, 27, and 30 July; and on 2, 6, 10, 17, 21, 24, and 30 August 2012.
This trial was conducted during 2012 at a small-scale organic farm located in Reno County, KS (38.094 N, 97.7413 W). Soils consisted of Pratt-Turon fine sands (pH=5.8). This trial was managed in four rows 22 m rows in the open-field. This trial was grown using organic practices but not located on certified organic land. Cherokee Purple was used as the nongrafted control and as scion in the grafted treatments. Vines were trellised using 60 cm (diameter) x 1.8 m tall tomato cages made from metal wire fencing. Every plot contained four plants with in-row spacings at 90 cm apart and row spacings at 1.8 m. Each replication was planted in a 22 m row with a total of four rows. Water was applied through drip irrigation, and straw mulch was applied for weed suppression. All treatments were transplanted into the field on 20 April. Harvesting occurred on 2,9, 12, 15, 18, 20, 23, 25, 29, and 31 July; 2, 5, 9, 12, 16, and 20 August; 7, 16, and 21 September; and finally on 12 October, 2012.
The data from each location/year were treated similarly but were analyzed independently. All data were analyzed using analysis of variance (PlotIt, Scientific Programming Enterprises, Haslett, MI), and where significant treatment effects were identified, a mean separation test was carried out using an F protected least significant difference (LSD) test. Total (both marketable and culled fruit) and marketable yield were converted to reflect tonnes/hectare (t/ha) in the table.
2012 Experimental Greenhouse Trials
Experiments were conducted at two greenhouse locations: Throckmorton Plant Sciences Center at Kansas State University (Manhattan, KS; http://www.hfrr.ksu.edu/p.aspx?tabid=38) and the K-State Olathe Horticulture Research and Extension Center (OHREC) located in Johnson County, KS (38.884347 N, 94.993426 W). All experiments were conducted in a split-plot randomized complete block design (RCBD) layout with three and four replications over time at the Manhattan and Olathe locations, respectively. The main plot factor was chamber design (described below), with four chamber designs tested in Manhattan and five tested in Olathe. The sub plot factor was grafting method, with standard and shoot removal (SR) techniques tested in Manhattan and standard, SR, and leaf removal (LR) tested in Olathe. Those methods are described in detail below.
Plants were self-grafted by grafting back onto the original root system with a commercial scion/nongrafted cultivar, ‘Cherokee Purple’ (Johnny’s Selected Seeds; Winslow, ME USA). Self-grafting allows that the plants experience the grafting process without adding variables such as genetic incompatibility and/or inconsistent rootstock and scion angles during the grafting procedure. Using this method, we were able to focus upon the influence of environmental factors post-grafting.
During grafting, standard, shoot removal (SR), or leaf removal (LR) techniques were applied to scion shoots. The standard grafted plants retained all meristematic and foliar tissue, while the SR grafted plants were cut 1-2cm above the scion cotyledon. The LR technique is a middle-ground approach, where most mature leaf tissue (70-80%) was severed but the plant meristem remained intact.
Plants were grafted on-site at each location with trained personnel and careful steps were taken to reduce bias between individuals. Each person performing the grafting process grafted the same proportion of plants for each chamber and grafted an equal number of plants within each sub-plot treatment (grafting method).
Five chamber designs, ‘humidifier’, “plastic”, “shade”, “perforated plastic” and a no-chamber control (“none”) were tested in Olathe. All treatments except perforated plastic were tested in Manhattan. The ‘humidifier’ chamber was built to specifications as described in Rivard and Louws, 2010 and is typical for small-scale propagators grafting more than 5000 plants per batch. It included a 4 mm plastic covering that encompassed the entire chamber as well as 55% shade cloth across the top and a cool-mist humidifier (SU-2000, Sunpentown, City of Industry, CA) located outside of the chamber. The humidifier delivered water vapor via PVC tubing (3 cm diameter). The ‘plastic’ chamber was identical to the ‘humidifier’ chamber except that a humidifier was not utilized. In both the “humidifier” and “plastic” treatments, 2 cm of water was added and maintained in the chamber floor for additional humidity. The ‘shadecloth’ chamber was covered with 55% shade cloth and lacked standing water or a humidifier. The ‘none’ chamber was completely vulnerable to greenhouse conditions with no environmental controls. Trays of grafted plants were placed on top of upside down clean propagation (web) trays to elevate grafted plants 5 cm above the floor of the chamber to keep them out of water where plastic coverings were utilized. Upside-down trays were arranged in the same manner to all treatments within the experiment in order to reduce bias that may be caused by tray elevation within the greenhouse. All healing chambers were built to dimensions of 0.91 x 1.22 m x 0.60 m using plastic lumber with steel wire hoops for holding plastic off of the plants. All chambers included a standardized frame with 2.5 cm x 13.6 cm plastic lumber whereby the width of the board (13.6 cm) was used to create a sidewall for the chamber. Holes were drilled into the top of the board to accommodate insertion of the steel wire on that was placed vertically into the top edge. Nine gauge wire was cut to equal lengths and inserted so as to permit a small chamber 60 cm tall at the peak.
For each replication and across both studies, the grafting day was indicated as Day 0. On Day 0 for each replication, 150 plants from each grafting method were placed in each healing chamber. In Manhattan, 150 standard grafted and 150 SR grafted plants were placed in each of the four chamber designs, for a total of 1200 plants. In Olathe, 100 standard grafted, 100 SR, and 100 LR were placed in each of the five chambers. The ‘humidifier’ and ‘plastic’ treatments employed full shadecloth coverings and were briefly vented daily until Day 5, when the shade cloth was turned back halfway to provide partial light exposure.. The humidifier was removed from the ‘humidifier’ treatment on Day 7. All plants were removed from the chambers on Day 8 and watered daily.
Environmental conditions within each chamber were monitored via temperature and relative humidity data loggers (EL-USB-2-LCD, Lascar Electronics, Erie, PA). A logger was placed among the seedlings in the center of each chamber and recorded environmental data at thirty minute intervals. The data loggers were activated once all seedlings were placed within the chambers and synced by using a delayed start function. Temperature and relative humidities from Day 0-8 averages, minimums, and maximums were analyzed using analysis of variance (PlotIt, Scientific Programming Enterprises, Haslett, MI). Where significant treatment effects were identified, a mean separation test was carried out using an F protected least significant difference test. In order to observe daily fluctuation in temperature and relative humidity for each of the healing chamber treatments, the average across replications for relative humidities and temperatures during the first full day after grafting for each replication (Day 1) were calculated.
Replication 1 was seeded on 22 January 2013 and subsequently transplanted into 50-cell trays on February 8. Grafting of the first replication took place on 23 February. Replication 2 was seeded on 31 January, transplanted on 15 February, and grafted on 1 March. Replication 3 was seeded on 23 February, transplanted on 13 March, and grafted on 28 March.
Replication 1 was seeded on 1 February 2013 and transplanted on 15 February. Grafting of Replication occurred on 1 March. Replication 2 was seeded on 22 February, transplanted on 1 March, and grafted on 15 March. Replication 3 was seeded on 1 March, transplanted on 15 March, and grafted on 25 March. Replication 4 was seeded on 15 March, transplanted on 29 March, and grafted on 8 April.
Throughout the two-week period of each replication, wilt ratings were recorded for each treatment, although this data is not shown. On day 14, plant survival was observed and recorded. All survival data were analyzed in SPSS (IBM, Armonk, NY) and showed no significant deviation from variance homogeneity; additionally, skewness and kurtosis statistics showed that survival data is approximately normal. Percent survival were calculated and analyzed using analysis of variance (PlotIt, Scientific Programming Enterprises, Haslett, MI). Where significant treatment effects were identified, a mean separation test was carried out using an F protected least significant difference test.
2011/2012 Field Research Trials
Grafting with inter-specific rootstock significantly increased yield in five of the six tomato trials reported here (P<0.05) and this effect was particularly pronounced in the high tunnel trials. Increases in yield when comparing the standard grafted plants with nongrafted controls ranged from 18% to 126%. The average yield increase when Maxifort rootstock was utilized was 53% across all the trials. Similarly, the average yield benefit with the use of ‘Trooper Lite’ rootstock was 51%. This data indicates that both rootstocks were successful at increasing fruit yield for tomato growers in the Great Plains and were similar when compared to each other using the standard tube-grafting technique. It is not clear why the effect of grafting was so pronounced in 2011 as compared to 2012 at the Johnson County on-farm location. Nongrafted marketable and total yields were particularly low in the Johnson County on-farm trial in 2011 as compared to 2012. This data suggests the ability of grafted plants to perform well during years with poor growing conditions for tomato production.
The effect of shoot removal on plant performance was not as consistent as grafting across all six of the trials. However, some trends can be observed, particularly as fruit yield of grafted plants is related to rootstock vigor. Overall, the effect of shoot removal reduced performance of the grafted plants as it relates to final plant yield. Across all of the six trials, observations can be made for both total and marketable fruit yield, comprising twelve comparisons in total. Out of the twelve comparisons, Maxifort increased fruit yield in eight of these and was not significant at two locations. Similarly, when Maxifort was grafted using the shoot removal (SR) technique, significant increases were seen in seven of the twelve comparisons for total and marketable fruit yield. When comparing ‘Trooper Lite’ in the same manner, significant yield increases were seen in seven of twelve comparisons for the standard grafting technique, but only five of the twelve comparisons for the SR-grafted plants (P<0.05). Interestingly, in four comparisons, SR-grafted ‘Trooper Lite’ had significantly lower fruit yield than standard-grafted ‘Trooper Lite’ plants (P<0.05) whereas all plants grafted with Maxifort had statistically similar fruit yield. These results suggest that ‘Trooper Lite’ was penalized by the shoot removal technique as this procedure reduced fruit production in four of the trials reported here. One explanation for this could be a lack of vigor by ‘Trooper Lite’ as compared to Maxifort. Removal of the shoot during the grafting procedure results in a smaller transplant at planting with fewer and/or smaller developed leaves. These plants are therefore required to grow faster in order to catch up to their counterparts grafted with the standard technique. Shoot biomass was significantly increased in four of the six trials by Maxifort and only one of the six trials by ‘Trooper Lite’ (P<0.05) when the standard grafting technique was utilized. This indicates that Maxifort increased vigor that was not provided by ‘Trooper Lite’. For future studies, a comparison of non- or self-grafted plants that have undergone the shoot removal process would be advantageous for determining its effect upon mature plant yield.
An important question concerning the utilization of grafted plants is to compare crop yields of grafted and nongrafted plants, particularly as they relate to early vs. mid- and late-season production. Because grafted plants with their shoots removed may be smaller at the time of planting, they may reduce the early-season yield as compared to plants with the standard grafting method. An examination of the cumulative yield curves indicate that although SR-grafted plants may perform similarly when final yield is tabulated at the end of the year, it could have negative effects on early and mid-season production.
At the Olathe Horticulture Center in 2011, ‘Trooper Lite’ provided the highest early-season production, including treatments where the SR technique was performed. Conversely, SR-Maxifort plants had lower early-season yields and caught up with standard grafted plants 90 days after planting. In 2012, early season yield was fairly similar across all treatments, but SR-‘Trooper Lite’ had lower cumulative yield than the other treatments until 70 days after planting when yields were comparable among all treatments. Similar to 2011, the benefit of using the SR-Maxifort and SR-‘Trooper Lite’ plants in 2012 was not equal to the standard-grafted plants until 125 days after planting. At the Johnson County on-farm location, both SR-grafted treatments showed a dramatic lag in yield as compared to standard-grafted plants in both years. Similarly to the OHREC trials, cumulative fruit yield increased among the SR-grafted plants during the mid- and late-season, and no statistical differences were seen between the standard- and SR-grafted plants in 2011 (P<0.05). In 2012, however, cumulative fruit yield of SR-grafted plants was not able to catch up to standard-grafted plants and statistically significant differences were seen. Interestingly, in the 2012 study, the nongrafted plants produced much higher yield early in the season and then provided little additional fruit production in the mid- and late-season. In the Wyandotte County trial, a pronounced yield lag can be observed by the SR-‘Trooper Lite’ and SR-Maxifort treatments. Plants grafted with the shoot removal technique had lower yields than all other treatments until 100 days after planting and final total yield was statistically similar to nongrafted plants.
Conversely to the other trials reported here, the SR-grafted plants did not reduce early season production in the Reno County on-farm trial, and the data suggests that these plants benefited from shoot removal (P<0.05). It should be noted that in contrast to the sites, this trial utilized an heirloom, indeterminate cultivar and the plants were grown in cages at a much lower planting density and in the open-field. It could be suggested that the added leader of the plant as a result of shoot removal was successful at increasing leaf area and therefore overall crop vigor and yield. Furthermore, the increased plant spacing allows for the efficient use of larger vegetative growth.
These trials indicate that tomato grafting is a viable and potentially profitable practice for organic/small-acreage growers in Kansas. Previous reports demonstrated that profitable yield increases may occur in grafted vegetable crops, when few biotic stressors are present (Ruiz and Romero, 1999; Yetisir and Sari, 2003). Our study suggests that grafting with inter-specific hybrid rootstocks, Maxifort and ‘Trooper Lite’, increases fruit yield when little disease pressure is evident in high tunnels, which are commonly utilized for tomato production on small farms (Carey et al, 2009). Both rootstocks conferred a significant increase in yield compared to the nongrafted plants when the standard tube-grafting method was utilized.
The effect of shoot removal was less consistent across the six trials and seems to be affected by rootstock cultivar. Final yield was not affected when Maxifort rootstock was grafted using the SR technique as compared to ‘Trooper Lite’. Maxifort is an especially vigorous rootstock and has shown yield increases in previous studies (Rivard and Louws 2010b), and particularly during the later part of the season (Rivard and Louws, 2008). However, both rootstocks exhibited a lag in production during the early harvest period (up to 100 days after planting). Removing the shoot was observed to reduce early season plant growth especially in the first 2 to 3 weeks after transplanting (data not shown). This suggests that the required re-growth of the scion tissue after removing the shoots resulted in lower yields than standard grafting methods; therefore, ‘Trooper Lite’ rootstock grafts may require a longer recuperation period while Maxifort-grafted plants may recover more quickly.Plant growth effects were significantly higher among the standard Maxifort grafts than the nongrafted plants whereas ‘Trooper Lite’ was not as vigorous which would explain the rootstock effects seen in our study. The added growth rate of the plants grafted with Maxifort was able to compensate for the required re-growth needed for the removed shoots. Rootstock vigor may be an important consideration for growers wishing to utilize the SR technique.
This data suggests that grafting could be a highly advantageous technology for high tunnel growers in the Great Plains. Grafting is a beneficial option in terms of yield for growers, but growers interested in on-farm grafting (as opposed to purchasing grafted plants) may discover many challenges in terms of grafted propagation. Therefore, simplified techniques that require less intensive management are critical for adoption of grafting for tomato growers. Although the shoot removal technique may not be a consistent method in terms of mature plant yield, it may be a valuable technique when used with certain rootstocks to boost yield and simplify the grafting procedure.
2012 Greenhouse Experiments
Relative humidity was highly impacted by healing chamber design in both studies. At the Manhattan location, the ‘plastic’ and ‘humidifier’ chambers showed a significant increase (P<0.01) in minimum and average relative humidity compared to the ‘none’ and ‘shadecloth’ treatments. There were no significant differences in maximum relative humidity in Manhattan. High relative humidity is common in greenhouses of this type on cloudy days and one or two particularly humid days make it difficult to assess the impact of maximum RH on grafting success. At OHREC, comparable results were observed, where the ‘plastic’ and ‘humidifier’ treatments had significantly greater average, minimum, and maximum relative humidity than the other three treatments (P<0.01).
Daily fluctuations in both temperature (°C) and RH (%) were observed in all chambers at both greenhouses, which represents the mean value of all replications for each site over a 12-hour period on day 1, post-grafting. As temperatures increase throughout the day, warm air expands and permits a greater water-holding capacity. If relative water vapor content in the area remains constant, the relative humidity will decrease as temperature increases. The chambers with little to no modification in humidity (‘none,’ ‘shadecloth,’ and ‘perf’) showed wider ranges in overall RH compared to ‘humidifier’ and ‘plastic’ treatments. Interestingly, higher humidity in the ‘humidifier’ treatments seemed to mediate higher temperatures, especially when related to ‘plastic’ treatments, although this trend was not statistically significant.
Healing chamber design had few significant effects on temperature at both locations. In Manhattan, no significant difference was observed in average, minimum, and maximum temperature. Growing conditions for both studies were ideal for grafting as late winter and early spring weather in the Midwest provides ample cloud cover to prevent healing chambers from over-heating in the greenhouse. This may have been a factor that led to high grafting success and little separation of the treatments overall. Unfortunately, incoming light measurements were not taken. Future studies of this type would benefit from this data as it could be correlated with healing chamber temperature fluctuations and overall grafting success. At the OHREC greenhouse, the ‘none,’ ‘plastic,’ and ‘humidifier’ chambers all had significantly greater average temperatures than the ‘shadecloth’ and ‘perforated plastic’ treatments but they were still all within 1 degree Celsius (P<0.05).
In both studies, no significant interactions were observed between the treatment main effects and grafting technique sub-effects. Plant survival ranged from 91% to 95% and no significant differences were observed between healing chamber treatments or grafting technique. Plants in the ‘none’ treatment and ‘shadecloth’ treatment exhibited more average wilting than those in the ‘plastic’ and ‘humidifier’ chambers (P<0.05), which were statistically similar to each other. These results indicate that plant stress was reduced with increasing levels of humidity.
Similar to the experiment in Manhattan, healing chamber treatments had no effect on graft survival in the Olathe study, which ranged from 77% to 87% across the different chamber types. However, the main effects of grafting method showed that plants grafted with the leaf removal (LR) technique had higher survival than the other grafting methods at 84% (P<0.05) across all the chamber types. Plants grafted with the shoot removal technique had similar wilt ratings as the LR plants and were lower than plants grafted with the standard method (P<0.05).
Grafting tomatoes with inter-specific rootstock is an effective method for reducing the incidence and/or severity of soilborne diseases in the United States (Louws et al., 2010), but the lack of grafted plants available for purchase by small growers can be a major barrier for adoption of this technology (Kubota et al., 2008). Many small-acreage growers are very interested in performing their own grafting, but management of the healing chamber can be difficult (Groff, 2009; O’Connell et al., 2009), particularly when limited propagation facilities are available. In this study, we tested the effect of healing chamber design on environmental conditions as well as grafting success. In our study, we saw no significant effects of healing chamber design on grafting success, and plants grafted with no chamber had success rates of 81% to 91%. Similarly, we saw no effect of using a cool-mist humidifier, which is often recommended for small growers propagating their own plants (Rivard and Louws, 2010). Our data suggests that a humidifier may not be necessary and similar results were seen by Johnson and Miles (2011). The ‘shade cloth’ treatment performed very well in our studies and was also successful for tomatoes in the study reported by Johnson and Miles (2011). Growers may experiment with chamber modifications in order to reduce the risk of “over-heating” in the greenhouse and our study provides information related to the effects of chamber coverings on environmental conditions.
Another approach for lowering water stress in the scion is the removal of leaves in order to reduce transpiration within the scion tissue post-grafting. In our study, removal of scion leaves increased plant survival compared to standard controls, but removal of the shoot did not affect percent plant survival. It must be noted that self-grafting of these plants presented a best-case scenario, and No statistical interactions were seen between healing chamber design and grafting method. Removal of the shoot and meristem requires that the plant re-initiate a meristem at the cotyledon leaves in addition to healing the graft union. Furthermore, we saw in preliminary studies that SR plants are susceptible to plant death by being shaded out by standard-grafted plants (data not shown). This indicates that the plants may not possess enough stored sugars in order to heal the graft union and develop a meristem before photosynthesis is re-initiated post-grafting. The leaf removal (LR) method tested in our studies showed significant promise and plants grafted using this technique had significantly higher success rates as compared to standard- and SR-grafted plants (P<0.05). Leaf removal may be recommended as a way to reduce water stress in the plant, and could potentially be a way to simplify the grafting process for small-scale propagators. A clear question for future research in this area is to determine how leaf and/or shoot removal affects the performance of mature plants in the field. The re-growth required as compared to plants grafted using the standard method may delay early growth and subsequent fruit production.
Carey, E.E., L. Jett, W. J. Lamont, T. T. Nennich, M.D. Orzolek, and K.A. Williams.
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Fernandez-Garcia, N., V. Martinez, A. Cerda, and M. Carvajal. 2002. Water and nutrient uptake
of grafted tomato plants grown under saline conditions. Journal of Plant Physiology
Groff, S. 2009. An economic comparison of grafted tomato transplant production
and utilization in multi-bay high tunnels.
Johnson, S.J. and C.A. Miles. 2011. Effect of healing chamber design on the survival of grafted
eggplant, tomato, and watermelon. HortTechnology. 21:752-758.
Kubota, C., McClure, M. A., Kokalis?Burelle, N., Bausher, M. G., and Rosskopf, E. N.
2008. Vegetable grafting: History, use, and current technology status in NorthAmerica. HortScience. 43:1664?1669.
Lee, J.M. 1994. Cultivation of grafted vegetables: Current status, grafting methods, and benefits. HortScience 29: 235-239.
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pathogens, foliar pathogens, arthropods and weeds. Sci. Hort. 127:127-146.?
?O’Connell, S., Hartmann, S., Rivard, C. L., Peet, M. M., and Louws, F. J. 2009.
Graftingtomatoes on disease resistant rootstocks for smallscale organic production.
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cucumber, caused by Fusarium oxysporumf. Sp. Radicis-cumcmerinum, by grafting onto
resistant rootstocks. Plant Disease. 86:379-382.?
Pogonyi, A., Z. Pek, L. Helyes, and A. Lugasi. 2005. Effect of grafting on the tomato’s
yield, quality and main fruit components in spring forcing. Acta Alimentaria
Rivard, C.L. and F.J. Louws. 2006. Grafting for Disease Resistance in Heirloom Tomatoes. Ag- 675: Extension Factsheet. College of Agriculture and Life Sciences, North CarolinaCooperative Extension Services.?
Rivard, C. L., and Louws, F. J. 2008. Grafting to manage soilborne diseases in
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interspecific rootstock provides effective management against diseases caused by
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Educational & Outreach Activities
Proceedings and Abstracts
- S.A. Masterson and C.L. Rivard. 2013. Advances in Grafting Technique and Healing Chamber Design for Tomato. Proceedings of the 2013 Methyl Bromide Alternatives Conf. (San Diego, CA)
- S.A. Masterson, M. Kennelly, R. Janke, and C.L. Rivard. 2012. Grafting methods and rootstocks for organic and heirloom tomato growers in the midwest. HortScience (Abstr.)
- S.A. Masterson. 2013. Propagation and Utilization of Grafted Tomatoes in the Great Plains. MS Thesis. Kansas State University, Department of Horticulture, Forestry, and Recreation Resources.
- S.A. Masterson. “Tomato Grafting Research at K-State”. 2013 Growing Growers Advanced Workshop: Tomato Grafting Benefits and Technique (Olathe, KS)
- S.A. Masterson. “Evaluation of rootstocks and grafting methods for high tunnel tomato production”. 2012 Central Kansas Market Farmer’s Conference and Tomato Grafting Workshop (Wichita, KS)
- C.L. Rivard and S.A. Masterson. 2013. Advances in Grafting Technique and Healing Chamber Design for Tomato. 2013 Methyl Bromide Alternatives Conference. (San Diego, CA). 6 November 2013
- Rivard, C.L., 2013. Benefits and utilization of grafting for US tomato production. University of Missouri Plant Science Division Seminar Series. 3 April 2013.
- Rivard, C.L., 2013. Vegetable grafting as an IPM strategy for US tomato production. Johnson County Community College Horticulture Sciences Day. 15 February 2013.
- Rivard, C.L., 2013. Benefits and utilization of grafting for US tomato production. Iowa State University Departmental Seminar Series. 11 February 2013.
- C. Rivard, D. Pryor, and S. Masterson. 2013. All about Tomato Grafting (5 part series). KSRE YouTube Channel. http://www.youtube.com/watch?v=h0YjlHyYywE
The results of our work have made tremendous impacts on the productivity and profitability of local tomato growers. Our studies showed that the utilization of grafted plants increased fruit yield by an average of 52%. This dramatic increase in yield can significantly increase productivity on a per plant basis, which is particularly useful in high tunnel systems. Furthermore, we have shown that utilizing grafted plants under low disease pressure is still advantageous for growers. This means that growers can utilize disease-resistant rootstocks in order to prevent the introduction and spread of soilborne pathogens, and that this practice is an economically viable tool for preventing disease epidemics in the long term. Additionally, the propagation studies conducted during this project will make medium-term impacts towards providing growers with accurate information related to healing chamber design. We have shown that simple chambers can be utilized for grafting tomato including the use of shade cloth alone. This was an unexpected finding and may be very useful for growers as shadecloth chambers are much easier to manage and may not require advanced greenhouses that have cooling systems. Finally, the leaf removal (LR) technique described in the greenhouse study significantly increased grafting success and could be a very useful technique for small-scale growers that are new to grafting. This method showed excellent promise as it was very simple, requires less management post-grafting, and did not appear to penalize plant growth as compared to the shoot removal (SR) method. Further research will be required to determine the effect of this grafting method on mature plant yield. However, anecdotal evidence indicates that this could be a very promising technique.
A detailed economic analysis was not proposed in this project. However, the results of the field studies will make significant economic impacts for growers as illustrated by testimonials of our collaborating growers.
This work was instrumental at leading to behavior change among growers and has built knowledge that will help propagators develop effective grafted plant production systems. One of our participating on-farm collaborators (Gieringer’s Orchard) has transitioned entirely to the use of grafted plants for the 2014 season. This includes 6 high tunnels and represents approximately 2500 grafted plants. Other growers in the state and region have also began using grafted plants, many of which were purchased from an aspiring grafted propagator in Lawrence, KS (Nathan Reed, LLC). Nathan attended our workshop held in March 2013 and has been active at starting a grafted plant business. During the 2013 growing season, produced several thousand grafted plants which were sold to numerous (>6 growers). Other growers in the region have began experimenting with growers and we have communicated with at least 10 that have utilized grafted plants, many of which gained interest as a result of the field work that we conducted in 2011 and 2012. Finally, this work has made national impacts through Dr. Rivard’s extension work including one-on-one consulting with at least 3 propagators in PA, NC, and CA. In particular, the results of the greenhouse studies were very well received by a national audience at the Vegetable Grafting Symposium held in San Diego, CA during fall 2013, which was attended by large-scale growers and propagators of grafted plants.
Areas needing additional study
One particular area needing additional study is the performance of the leaf removal (LR) plants during fruit production. We added the LR treatment during our greenhouse studies as a results of observations of poor plant growth by the SR treatment. In the case of the LR method, all leaves are removed from the scion during grafting, but the meristem is left in tact. This significantly improves the re-growth of the scion while reducing the transpiration and subsequent water stress of the scion post-grafting. We found that in our studies the plants that had undergone the LR method quickly recovered and were much more capable of catching up in vegetative growth to the nongrafted and standard-grafted plants than the ones where the SR method was performed. Due to the late timing of this discovery, we were not able to include this treatment in any of the field experiments. Based on our findings that the SR method penalized mature plant performance, it appears that the LR method may be very advantageous for small-scale growers and/or propagators with limited resources and would probably perform better than the SR method.