Evaluating Sustainable Alternatives of Rootstock Selections in Grafted Tomatoes to Enhance Yield Potential in High Tunnel and Field Production

Project Overview

GNC15-215
Project Type: Graduate Student
Funds awarded in 2015: $9,900.00
Projected End Date: 03/31/2018
Grant Recipient: University of Minnesota
Region: North Central
State: Minnesota
Graduate Student:
Faculty Advisor:
Dr. Emily Hoover
University of Minnesota

Annual Reports

Commodities

  • Vegetables: tomatoes

Practices

  • Crop Production: grafting, plant breeding and genetics, seed saving
  • Education and Training: demonstration, youth education

    Abstract:

    Introduction/Summary:

    Tomatoes, especially heirloom varieties that often are susceptible to many soil-borne diseases, are a popular and profitable crop for market farmers. After continuous production, disease pressures within soil reduce yield without either chemical treatment or alternative practices.

    Grafting heirloom scions to disease resistant root stock has been shown to be an effective method of mitigating the problem with disease load in soils. Grafting to commercial hybrid root stock seed is the current practice. Many open pollinated and hybrid tomato seeds are bred to suppress several of the same diseases controlled by the many commercially available root stock cultivars. Sustainable production practices discourage the purchasing of off-site inputs. The expensive commercially available root stock seed is typically 100x the cost of alternative hybrid and open pollinated seeds.

    This study was designed to evaluate a more sustainable production alternative by determining the relative advantage of using “saved seeds” from open-pollinated tomato varieties shown to suppress diseases. The primary objective was to increase yields. It was demonstrated that saved seeds from open pollinated varieties provide an effective root stock alternative for grafting onto heirloom varieties (scions) that cannot be produced without treatment in soil containing high disease loads.

    Saving seeds from parent plants exhibiting improved production qualities and inherent natural disease resistance had been a practice traditionally used by farmers to provide site-specific improvements in yield. Although saving seeds has not been practiced by most contemporary farmers, revisiting this practice may offer an additional advantage as a source of disease suppressing root stock when grafting to scion varieties that cannot survive without treatment.

    This study was designed to first determine whether the apparent disease suppression qualities of tomato plants found to survive in soils containing disease pressure could be inherited by the subsequent generations within three open-pollinated varieties: Large Red Cherry, Roma, and Rutgers. Even as the disease load in the test soil plots increased each year, saving seeds from viable parent plants resulted in an increasing percentage of surviving plants that produced salable tomatoes. This would indicate that the disease suppression is a genetic trait that can be positively influenced by seed saving.

    After three seasons of saving seeds from the plants that demonstrated superior disease resistance that were raised in soil contaminated with Fusarium species, the seeds from resistant offspring were used in the 2017 growing season as root stock for a grafting study. A commercially popular and well-studied root stock, RST-04-105T, was compared to the open-pollinated root stocks, traditional hybrid tomato varieties (Celebrity and Early Girl), and controls. Several tomato cultivars, including many heirloom varieties known to lack inherent disease suppression, were compared in many growing conditions, under different grafting techniques, and with different root stocks to determine whether grafting provides farmers an advantage over non-grafted tomatoes.

    The primary objective was to increase yields using production techniques that increase sustainability. This study found that this objective could be met through two primary practices. First, by encouraging farmers to returning the practice of saving seeds from open pollinated varieties as a method of naturally reducing losses from soil-borne diseases in both traditional (non-grafted) production and with tomato production utilizing grafting. Second, encourage farmers to include grafting of tomatoes when crop rotation cannot mitigate disease pressure (typically in high-tunnels) or when highly susceptible heirloom varieties are grown. Although requiring “off-site” purchases, under some circumstances, grafting to commercially available root stock offerings may be the best choice.

    The resulting outcome did not fully meet the desired result. The first objective, showing the advantages of saving seeds, had very positive results. Farmers can provide ongoing site-specific advantages in both traditional (non-grafting) and grafting production by saving seeds from open pollinated tomatoes demonstrating superior performance. The second objective also demonstrated that grafting can provide farmers an advantage in increasing yields, especially with heirloom varieties of tomatoes. However, the commercial variety RST-04-105T, outperformed all other root stocks with all scions tested.

    Although the root stock alternatives from saved seeds used in this study demonstrated great advantages over non-grafted and self-grafting (same variety as both root stock and scion) controls (63-92% increase in yield compared to controls with the "Large Red Cherry" variety), they failed to meet the effectiveness of the RST-04-105T (58-117%), especially with high tunnel production.

    The broader range of diseases controlled by the RST-04-105T compared to others tested may likely explained why the commercially breed root stock consistently produced the greatest yield in each of the scions tested. The greater root mass of the RST-04-105T compared to other root stocks tested may also suggest that other factors, such as greater Mycorrhizal colonization may have been a factor.  Growers need to consider all the potential soil borne diseases and select root stock that can suppress the greatest range of possibilities. We focused on selecting root stock varieties for Fusarium species, the primary disease issue we experience within our soils. It is likely that multiple soil-borne diseases were present and had an influence on yield.

    The additional cost (an additional $.73/grafted unit increase) of using the RST-04-105T seed may not justify the production increases that were achieved because production increases did not occur with the RST-04-105T grafted plants until the end of the season (October) when production often exceeds potential sales. The advantage of the RST-04-105T was not apparent until the days shortened, and the air/soil temperature dropped. This was especially apparent when comparing the field production yield to the warmer tunnel production in October. Growers who maintain production beyond the four months of harvest recorded in this study (July-October) may determine that the commercially sold root stock such as RST-04-105T may be the best alternative.

     

    Project objectives:

    The objective of this study was to increase yield in tomatoes with more sustainable production techniques. Two primary ideas were evaluated. Potential benefits of saving seeds to reduce disease issues and increase yield, and evaluating the potential of using open pollinated tomato varieties as a source of root stock for grafting.

    These objectives were evaluated by trials. No changes in the original experimental design was made. More extensive experimentation was performed on alternative grafting methods (age of plants at time of graft and side compared to tip graft). Additional varieties for both root stock and scions were added.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.