Grafting Rootstocks onto Heirloom and Locally Adapted Tomato Selections to Confer Resistance to Root-knot Nematodes and other Soil Borne Diseases and to Increase Nutrient Uptake Efficiency in an Intensive Farming System for Market Gardeners

Grafting Rootstocks onto Heirloom and Locally Adapted Tomato Selections to Confer Resistance to Root-knot Nematodes and other Soil Borne Diseases and to Increase Nutrient Uptake Efficiency in an Intensive Farming System for Market Gardeners

Summary

Grafted tomatoes were evaluated using organic practices on-farm and at a research station (CEFS) in 2006. Two 30 ft x 98 ft high tunnels were constructed in 2007 at CEFS for an in-depth replicated comparison with adjacent field plots of grafting treatments at 3 different planting dates and fertility levels. Grafted transplants were also evaluated in the NCSU Phytotron in two conventionally fertilized experiments. In preliminary data, specific rootstocks reduce bacterial wilt incidence. Yield advantages have not been significant, but cooperators are enthusiastic, and work is taking place both on-farm and at CEFS to optimize training and rootstock/scion combinations. The outcome of this work is to offer a systems approach to understanding the utility of high tunnels, grafted tomatoes, and the integration of the two technologies for stable and more profitable tomato production.

Objectives/Performance Targets

1. 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.

Accomplishments/Milestones

1. 1. Improve grafting, acclimation and transplanting techniques: We have improved our techniques, especially the performance of the acclimation chamber. Currently chambers are located in the NCSU Phytotron under constant temperature conditions. We have modified misting practices to reduce water deposition on the leaves. Excessive deposition can break off the fragile graft junction because of the weight of the water. Although most grafts were successful, we experienced germination problems with certain rootstocks and scions, as well as with the organic potting mixes and fertilizers used for the first time this spring. Changing the potting mix and reducing the fertilizer concentration have resolved these problems.

   2. Select appropriate rootstocks for root-knot nematodes and other soilborne diseases: Field trials were implemented in grower fields in 2006 to observe disease incidence and crop productivity of grafted tomatoes compared to controls under conditions with and without pressure from soilborne plant pathogens. In naturally infested soil, with high disease pressure from bacterial wilt, BW incidence was 75% in 2006 in the non-grafted treatments. Tomatoes grafted on the resistant genotypes CRA 66 and Hawaii 7996 showed no symptoms of wilt, however. Under conditions of little or no expected disease pressure, grafted transplants still performed as well or better than controls. On-farm research trials with ‘Maxifort’ and ‘Robusta’ rootstocks, which lack bacterial wilt resistance, but have most other common resistances to nematodes and soilborne diseases, indicated that grafting treatment did not affect total yield under a typical organic management system. Fusarium wilt, which appeared in the field unexpectedly, was significantly lower in scion grafted to the ‘Maxifort’ rootstock compared to non-grafted and self-grafted controls.

   3. Select appropriate rootstocks for increased nutrient uptake efficiency and other horticulturally valuable traits, such as fruit quality, earliness, vigor, and resistance to pests: ‘Maxifort’ is the most important rootstock utilized commercially in the US. It confers vigor, and has resistances to most of the major soilborne pathogens, including Corky root, Fusarium Races 1-2, Verticillium wilt and root knot nematode. Maxifort will be used in the replicated 2007 trials, as it performed well in 2005 and 2006 and is ‘standard’ in the US grafting industry. However, it is not clear whether more vigorous plants are desirable in all situations. Plants that are too big can be difficult to handle. Therefore we are trialing a rootstock ‘Beaufort’ which confers less vigor to the scion, and also one ‘Big Power’, which the distributor claims will make the plant less vegetative. Other rootstocks that will be trialed on a limited basis because of claimed superiority also include Dai Hon, Robusta and DP-105. At this point only limited numbers of rootstocks are offered for sale in the US, and we were not able to locate any rootstock specifically shown to improve nutrient uptake.

   4. Test training and establishment techniques for grafted rootstocks, including single and multiple head systems: We are continuing our work with training systems, and our on-farm cooperators are also experimenting. They have been pleased with the performance of grafted plants we provided, but felt the plants were too big to handle easily with their current trellising system. In 2005 Maxifort’ rootstock increased yield when a twin row training system was implemented. In 2006, ‘Maxifort’ significantly increased yield in both standard and twin row training systems (P=0.005), but no difference was found across the two training systems. Non-grafted plants and self grafted plants generated yields that were 54% and 77% of the yields generated using Maxifort rootstock. In 2007 we will be testing the standard and twin row systems again, but with modification of plant placement in the rows.

   5. Compare performance of scions grafted onto resistant rootstocks, self-grafted and non-grafted controls under realistic conditions of soilborne disease pressure: Field trials were implemented in 2005 and 2006 to observe disease incidence and crop productivity under conditions with and without pressure from soilborne plant pathogens. In naturally-infested soil at a cooperating farm, BW incidence was 79% and 75% in 2005 and 2006, respectively in the non-grafted treatments. However, the resistant genotypes CRA 66 and Hawaii 7996 showed no symptoms of wilt in either year. With the use of ‘Maxifort’ rootstock, Fusarium wilt incidence was significantly reduced in grafted plants as compared to non-grafted and self-grafted controls.

   6. Compare performance of scions grafted onto resistant rootstocks, self-grafted and non-grafted controls under optimal growing conditions on an organic research station: On-farm and research station trials with ‘Maxifort’ and ‘Robusta’ rootstocks indicated that grafting treatment did not affect total yield in a typical organic management system under conditions of moderate to low disease pressure from soilborne pathogens. Farmer cooperators were pleased with the performance of grafted tomato plants in 2006 and requested additional material in 2007. In one case, root knot nematodes appeared unexpectedly in one of the on-farm trial fields, and grafted plants may have offered additional protection, although this was not set up as an experimental variable, and cannot be directly tested. We have also conducted two experiments in the NCSU Phytotron utilizing conventional rather than organic fertilizers. In the first experiment Maxifort was grafted on ‘German Johnson’, a popular heirloom, and in the second, it was also grafted on ‘Trust’, a popular greenhouse hybrid since in the first experiment, ‘German Johnson was quite variable, even without grafting. No statistically significant differences in tissue nutrient content and biomass were seen between German Johnson grafted on Maxifort, German Johnson grafted on itself, and non-grafted German Johnson. There were also no interactions between grafting treatments and fertility levels. Grafted plants were consistently taller, however. Only a limited number of tissue nutrient samples could be analyzed however, and all plants experienced some stress, so the experiment is being repeated this spring with better replication and growing conditions, and more sampling. Final harvest has been made, but the tissue analysis and biomass determinations have not yet been conducted.

   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: Results from on-farm experiments are promising in terms of disease resistance and overall plant vigor, but we are just starting the tunnel and field comparisons of the grafted plant systems. We have contact an economist who is interested in collecting numbers on the economics of the high tunnel system. This aspect will be further developed in Year 2 of the project.

   8. Identify promising avenues for future research and development: This aspect will also be developed more in Years 2 and 3, but we have already started some small side studies on training systems and additional rootstock/scion combinations. In addition, economic aspects need further documentation when we feel we can identify standard recommendations. The microclimatic differences between tunnels and outdoors should be documented. In future research it would be good to gather data from various areas and try to construct climate/economic models indicating when and where tunnels can be most useful.

Impacts and Contributions/Outcomes

The interest in both grafting and high tunnels has increased greatly in the past year. Group members have been requested to give many talks and demonstrations on grafting and high tunnels. We have also received many more requests for grafted transplants than we could satisfy with available personnel and supplies. Specific events and activities included:
•Grafting demonstrations for students in Vegetable Crop Production (HS431) during two laboratory periods in Fall 2006
•Grafting demonstration for students in Greenhouse and High Tunnel Food Production (HS590C) in Spring 2007. Three students of the four students who were extension agents and one graduate student also incorporated grafting into their class project.
•Two graduate student and one undergraduate grafting research project took place.
•Grafted tomato seedlings were provided to 3 NC growers and one in Pennsylvania for on-farm research in replicated field trials. Growers were selected on the basis of their willingness to take data and on being leaders in the sustainable agriculture area.
•Invited season extension presentations on were given by Peet: Southeastern Veg. Expo 2006 Dec. 13, Myrtle Beach, SC: presented 30-minute talk; Presentations at High Tunnel Greenhouse Production Workshop, Oct. 16, Goldsboro, NC and Women in Agriculture regional Conference Raleigh, NC, Sept. 6, 2006, both on Season Extension; Grafting presentations by Rivard: Southeastern Veg. Expo 2006 Dec. 13, Myrtle Beach, SC: presented 30-minute talk; March 2007, Grafting workshop, Pittsboro, NC (also included Louws); SARE annual conference, July 2006; Sustainable Ag Conference in November 2006; Organic Growers School 2006 and 2007.
•CEFS tours have been held of the newly constructed research tunnels. A handout has been prepared for distribution to tour groups, and information will appear on the CEFS website.
•High tunnels and grafting have been added as topics to the Greenhouse Food Production Website
•A handout on grafting techniques was prepared and 1000 copies printed. Many copies have been distributed, and the handout is also available in .pdf format online.

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