An experiment comparing grafted and non-grafted specialty tomatoes for soil-borne disease resistance, yield, and fruit quality was conducted in an organically managed high tunnel at the Frog Song Organics farm, Hawthorne, FL. Four indeterminate, small-fruited cultivars selected by the grower were used, including ‘Sun Gold’, ‘Supersweet 100’, ‘Black Cherry’, and ‘Green Zebra’. They were grafted onto two commercial tomato rootstocks ‘Multifort’ and ‘Estamino’, with the non-grafted tomato scion cultivars as controls. Grafting was shown to be an effective tool for managing Fusarium wilt and improving the overall health of tomato plants. Total marketable yield was significantly improved in grafted tomato production compared with non-grafted controls in the organic high tunnel system. Some scion-rootstock interaction effects were observed in fruit quality assessment. Economic analysis indicated increased net returns as a result of using grafted plants regardless of the higher production cost. Research findings were disseminated through various workshops and presentations. This on-farm research project was a successful demonstration of technology transfer through a collaborative and productive partnership with local growers to address targeted production issues.
Objective 1. Determine the effectiveness of grafting with resistant rootstocks for controlling soil-borne diseases in heirloom and specialty tomatoes grown in organically managed high tunnel.
Objective 2. Assess fruit yield and quality as affected by grafting with vigorous disease-resistant rootstocks.
Objective 3. Analyze the costs and returns of high tunnel production of grafted tomatoes to determine its economic feasibility in a commercial operation setting.
We collaborated with the Frog Song Organics, a certified organic farm in Hawthorne, FL in this on-farm research project to conduct a site-specific evaluation of grafting as an economically feasible tool for soil-borne disease management in organic tomato production in the high tunnel system. Based on the growers’ interest and recommendation as well as the growing season during project implementation, we decided to focus on specialty tomatoes rather than heirloom tomatoes in this study. Four indeterminate tomato cultivars were selected for this grafted tomato study in an organically managed high tunnel (22 ft by 88 ft). These specialty tomato cultivars (Johnny’s Selected Seeds, Winslow, ME) differ in fruit size and color, including: ‘Sun Gold’ (bright tangerine-orange cherry tomato), ‘Supersweet 100’ (red cherry tomato), ‘Black Cherry’ (cherry tomato fruit almost black in color with dynamic flavor), and ‘Green Zebra’ (3-4 oz. green fruit with yellow blush and darker green stripes). In particular, the grower commented that ‘Black Cherry’ was highly susceptible to Fusarium wilt based on its performance in the previous season before this on-farm study. Two commercially available rootstocks ‘Multifort’ and ‘Estamino’ (Paramount Seeds, Inc. Stuart, FL), were used to graft the four tomato scion cultivars, respectively. According to the seed catalog, ‘Multifort’ is a robust interspecific tomato hybrid rootstock with great vigor which has resistances to Fusarium wilt, Fusarium crown and root rot, Verticillium wilt, root-knot nematodes, and corky root. ‘Estamino’ is a vigorous tomato rootstock with resistances to Fusarium wilt, Verticillium wilt, root-knot nematodes, and Fusarium crown and root rot, which is also claimed to produce a more balanced grafted plant favoring fruit production. Tomato scions ‘Black Cherry’ and ‘Green Zebra’ were seeded on 7 Oct. 2014 in the greenhouse for transplant production, while ‘Sun Gold’ and ‘Supersweet 100’ were seeded on 14 Oct. 2014. The rootstocks were also seeded on 7 and 14 Oct. 2014, respectively. There were eight scion-rootstock combinations with the four tomato scion cultivars grafted onto the two rootstock cultivars, respectively. Plants were grafted using the splice grafting method and the graft healing followed the procedure described by Djidonou et al. (2013a) with modification. Non-grafted tomato scion cultivars were used as controls in this study.
The on-farm experiment with eight grafted combination treatments and four non-grafted controls was arranged in a randomized complete block design with 3 replications and 5 plants in each plot (experimental unit). All the tomato plants were transplanted in the high tunnel on 23 Dec. 2014. Leafy greens were planted in the high tunnel prior to this experiment. The soil type is classified as Bonneau fine sand – loamy, siliceous, subactive, thermic Arenic Paleudults. The single-row unmulched raised beds were spaced 5.5 ft apart (between bed centers) with 2 ft in-row spacing. Tomato plants were trellised on 10 ft EMT pipes (7 ft aboveground, poles spaced every 6 ft) with Homestead style weave. Leaves were pruned to promote airflow, and to remove diseased tissue. Two drip tapes were used for irrigation in each bed with 12-inch emitter spacing. The irrigation scheduling was adjusted by the grower according to crop needs. Black Kow composted cow manure 0.5-0.5-0.5 (Black Gold Compost Company, Oxford, FL) was applied preplant at approximately 20 tons/acre. MicroSTART60 3-2-3 organic fertilizer (Perdue AgriRecycle, LLC, Seaford, DE) was applied preplant at the nitrogen (N) application rate of 54 lb/acre and was sidedressed in the beds at the same N rate during the production season in Feb. Based on disease and pest monitoring, Oxidate, Entrust, and Regalia products were used for foliar disease and pest management by the grower when needed. Two portable 23000-BTU kerosene heaters were used in the high tunnel during a few nights in the early season to protect the crop from frost and cold damage. Day-to-day crop management decisions were made primarily by the grower during this on-farm trial.
Fusarium wilt (caused by Fusarium oxysporum f. sp. lycopersici) and leaf mold (Passalora fulva) were identified as the main soil-borne and foliar diseases, respectively. A 0-4 rating scale (0 = healthy plant; 4 = plant dead) was used to assess the disease severity of every plant in each plot four times during May-June. After the final tomato harvest, two plants in each plot were dug out, and root-knot nematode galling was evaluated based on a 0-10 scale (0 = no galls; 10 = plant and roots are dead) (Zeck, 1971). The first harvest of tomato fruit began on 17 Mar. 2015 and was continued 2-3 times per week until 19 June 2015. Marketable and unmarketable fruit weight and number were measured at each harvest. Aboveground plant biomass (dry weight) was also measured after the final harvest. Representative fruit samples were collected for fruit quality assessment including soluble solids content, titratable acidity, and pH (Barrett et al., 2012). Data analysis was conducted using the Proc GLIMMIX procedure of SAS (version 9.3 for Windows; SAS Institute, Cary, NC). Fisher’s least significant difference test at P ≤ 0.05 was performed for multiple comparisons of different measurements among treatments.
Cost-return analysis was conducted to compare the profitability of using non-grafted vs. grafted plants in the organic high tunnel system. In addition to the estimated transplant costs, other variable and fixed costs of crop production were estimated for a partial budget analysis following the general procedure of our previous study on economic analysis of grafted tomato production (Djidonou et al., 2013b). The revenue per unit production area was calculated as revenue = yield × price, and the profit was calculated as profit = revenue – (variable cost + fixed cost). Change of profit as a result of using grafted plants was determined. Additionally, a sensitivity analysis was performed to capture the variation of net returns as influenced by market price of tomato fruit during the harvest period in order to offer growers a more comprehensive assessment of economic feasibility.
Barrett, C.E., X. Zhao, C.A. Sims, J.K. Brecht, E.Q. Dreyer, and Z. Gao. 2012. Fruit composition and sensory attributes of organic heirloom tomatoes as affected by grafting. HortTechnology 22:804-809.
Djidonou, D., X. Zhao, E.H. Simonne, K.E. Koch, and J.E. Erickson. 2013a. Yield, water-, and nitrogen-use efficiency in field-grown, grafted tomatoes. HortScience 48:485-492.
Djidonou, D., Z. Gao, and X. Zhao. 2013b. Economic analysis of grafted tomato production in sandy soils in Northern Florida. HortTechnology 23:613-621.
Zeck, W.M. 1971. A rating scheme for field evaluation of root-knot nematode infestations. Pflanzenschutz Nachrichten 24:141-144.
Grafting with the two rootstocks, i.e., ‘Multifort’ and ‘Estamino’ was shown to be highly effective in managing Fusarium wilt and improving the overall health of plants in this on-farm study of high tunnel production of organic specialty tomatoes. Fusarium wilt was observed and identified as the predominant disease problem in ‘Black Cherry’ and ‘Green Zebra’. Disease severity ratings were significantly lower in grafted plants than non-grafted controls by approximately 21% to 71%. The two rootstocks did not differ significantly in their effects, while ‘Black Cherry’ tended to be more susceptible than ‘Green Zebra’. Leaf mold was a major problem in ‘Sun Gold’ and ‘Supersweet 100’. Interestingly, grafted plants showed less severe symptoms of leaf mold in comparison with non-grafted plants, and the reduction ranged from about 25% to 31%. We were not able to compare the root-knot nematode infestation in plant roots between grafted and non-grafted plants as the roots of most of the non-grafted plants evaluated at the end of the season already decayed. The root galling rating did not differ significantly between plants grafted with the two rootstocks, while ‘Multifort’ grafted plants tended to exhibit a higher level of infestation than those grafted with ‘Estamino’. Visually, grafted plants demonstrated markedly greater vigor than non-grafted controls after the final harvest. A significant increase of 125% on average in aboveground biomass was observed in grafted plants as compared with non-grafted controls at the end of the season across different tomato scion cultivars. The improved plant health as a result of using vigorous, resistant rootstocks helped maintain plant growth and vigor throughout the season.
In addition to plant health improvement, tomato fruit yield enhancement was also found in this on-farm experiment. The marketable fruit yield increase in grafted plants primarily occurred in May and June. During Mar.-Apr., the grafting effect was only observed in ‘Sun Gold’ with plants grafted onto ‘Estamino’ showing significantly higher marketable fruit yield than non-grafted plants. The May harvest results demonstrated significantly improved marketable fruit yield in grafted vs. non-grafted plants for all the scion cultivars, while no difference was found between the two rootstocks. The yield increase caused by the use of grafted plants reached 139% (‘Sun Gold’) to 485% (‘Black Cherry’) depending on the tomato scion cultivar. Marketable fruit yields of non-grafted ‘Supersweet 100’, ‘Black Cherry’, and ‘Green Zebra’ were minimal as plants severely declined in June; however, grafted plants continued to produce marketable fruit, particularly ‘Green Zebra’ grafted onto the two rootstocks showed stable yields during the late season. With respect to full-season marketable fruit yield, all the tomato scion cultivars demonstrated significant improvement by using grafted plants. Compared with non-grafted controls, grafted plants resulted in higher total marketable yields by 51% (‘Sun Gold’) to 339% (‘Green Zebra’). The yield increase effect was similar between the two rootstocks used. In general, unmarketable fruit percentage was relatively low in this study. Except for ‘Sun Gold’, grafting also resulted in an increase in unmarketable fruit percentage. Average single fruit weight was comparable between grafted and non-grafted plants. Grafting did not exhibit any significant impacts on titratable acid and pH of tomato fruit, whereas some scion-rootstock interactions were observed with respect to soluble solids content. For instance, soluble solids content was increased by grafting with ‘Estamino’ in ‘Supersweet 100’; however, it was reduced by grafting with both rootstocks in ‘Green Zebra’.
The economic analysis results showed that the cost of some grafted transplants was as high as six times of that of non-grafted transplants. The revenue of grafted tomatoes, however, is sometimes as high as 4.5 times of that of non-grafted tomatoes. This can be attributed to the significant yield increase of grafted tomatoes and the high market tomato price received by growers. The grower operates an organic farm and mainly sells their product by direct marketing, therefore, can receive much higher price than those growers who sell their product to wholesalers. The high price received by the organic grower ($7.6/lb on average) further intensified the effect of yield increase of grafted tomatoes on farming profitability, resulting in much higher revenue from grafted tomato production in contrast to the use of non-grafted plants. Hence, although the production cost of grafted tomatoes is higher than that of non-grafted tomato production, the grafted tomatoes are more profitable considering the higher productivity of grafted plants. Sensitivity analysis showed that the economic advantage of grafted tomatoes was more evident with the decrease in the grafted transplant cost and the increase in the tomato price. It is noteworthy that even if the tomato price was reduced to $3.29/lb, grafted tomatoes could still result in higher net profit than non-grafted tomatoes.
In conclusion, this on-farm study of high tunnel production of organic specialty tomatoes demonstrated the effectiveness of using grafting with resistant and vigorous rootstocks for managing soil-borne diseases, improving plant health, and enhancing tomato yield and economic returns.
Educational & Outreach Activities
Zhao, X. 2015. Vegetable grafting workshop. Florida Local Food Summit. Gainesville, FL.
Zhao, X. 2016. Vegetable grafting workshop. Panhandle Fruit and Vegetable Conference, Marianna, FL.
Zhao, X. 2016. Tomato grafting workshop to master gardeners. Jacksonville, FL
Zhao, X. 2017. On-farm workshop: Tomato grafting for organic and high tunnel production. Frog Song Organics, Hawthorne, FL.
Zhao, X. 2017. On-farm workshop: Tomato grafting. Organic Food & Farming Summit, Hawthorne, FL
Zhao, X., Z. Black, D. Huff, and L. Khandaker. 2015. Grafting to improve specialty tomato production in an organically managed high tunnel system. 4th National Vegetable Grafting Symposium, Grand Rapids, MI.
Zhao, X. Z. Gao, O. Rysin, and F. Louws. 2016. On-farm economic impacts of using grafted plants in tomato production. The North Carolina Tomato Growers Association’s Winter Vegetable Conference & Trade Show, Asheville, NC.
Zhao, X. 2016. An overview of vegetable grafting. Epcot Agricultural Sciences Internship Program Seminar Series, Orlando, FL.
Zhao, X. 2016. Vegetable grafting. Presentation to the Suncoast Tropical Fruit and Vegetable Club, Nokomis, FL.
This on-farm research project was a successful demonstration of technology transfer through a collaborative and productive partnership with local growers to address targeted production issues. Development of this project is largely driven by grower’s interest and their active participation in improving long-term sustainability of vegetable production. Prior to this on-farm study, the grower had a complete crop failure with ‘Black Cherry’, a popular tomato cultivar in the local market, under high tunnel production due to the high pressure of Fusarium wilt. Grafting was introduced to them while they were searching for new management tools to improve their current production system. The lack of disease resistance in many of the heirloom and specialty tomato cultivars is a constant challenge for growers. By involving farmers in designing this project, our research findings provided up-to-date research-based information on using grafting with appropriate rootstocks to manage devastating pest problems in high tunnel production of organic specialty tomatoes. In the intensively managed organic high tunnel system, using grafted plants also allowed flexibility in crop and cultivar selection and rotation. At the end of the study, the grower was convinced that grafting can be used as an economically viable tool to help solve site-specific soil-borne disease problems. The grower was even considering using grafted plants for open-field production of tomatoes at the farm.
Results from this study will also be useful to other growers who are seeking non-chemical IPM tools for their production systems. Moreover, this on-farm project responds in a timely manner to the critical research needs for developing sustainable high tunnel cropping systems in the Southeastern Region to address production challenges associated with disease and pest problems and environmental stresses.