Published in Winter 2022
By: Alex Stone, Matt Davis, and Amy Garrett Oregon State University
Vegetable grafting is widely practiced worldwide as a soil borne disease management strategy, with disease susceptible varieties grafted onto disease resistant rootstocks. This practice
was first documented in Japan in the 1920s, with watermelons grafted onto squash rootstock (Kubota, 2016). Grafting of vegetables has not been widely practiced in the US until recently due to readily-available and cost-effective soil fumigants and the high labor costs associated with grafting; a growing interest in non-chemical soil borne disease control strategies and mechanization of the grafting process is expanding grafting interest and adoption in the US.
Vegetable grafting to improve drought and heat tolerance (climate resilience) is an emerging research area. In 2019, the OSU Vegetable Program/Stone laboratory, in partnership with the Small Farms Dry Farm Program, first compared Early Girl tomato grafted onto Fortamino rootstock with ungrafted Early Girl (WSARE project “Enhancing Vegetable Farm Resilience through Dryland Production”). Grafted Early Girl plants were less drought-stressed than ungrafted plants, and fruit yield and size were higher and blossom end rot incidence lower on grafted plants than on ungrafted plants. These results suggested that grafting is a promising strategy to improve dry farmed tomato productivity in the Willamette Valley.
The WSARE project “Production and Marketing of Dry-farmed Tomatoes in Oregon” began in 2020 and has trialed more than 200 tomato varieties and scion/ rootstock combinations for dry farm performance. In 2020, the project found that the rootstocks Fortamino, DRO141TX, Emperador, and Maxifort improved tomato dry farm performance, while Shin Cheong Gang did not. In 2021 (a hotter and drier year than 2020 with a record-setting heat dome in late June), DRO141TX, Emperador, and Fortamino were again shown to improve dry farm performance (Tables 1 and 2), with differences between DRO141TX and Fortamino detected. Across seven scions grafted onto them both, those grafted onto Fortamino exhibited lower blossom end rot incidence and were less drought-stressed, though a significant impact on yield and fruit size was not detected. Fruit of Big Beef and BHN-871 grafted onto either Fortamino or DRO141TX remained firm despite the extreme heat in 2021, while fruit of other combinations were unacceptably soft.
Summary
Grafting is a promising tool to improve dry-farmed tomato performance as it has the potential to reduce plant drought stress and blossom end rot incidence and increase fruit yield and size. Big Beef and BHN-871 grafted onto either Fortamino or DRO141TX rootstocks are highly recommended for dry farm production as these scion/rootstock combinations were high performing in 2020 and 2021 and produced the greatest yield of firm umblemished fruit in the extreme 2021 heat. Plants grafted onto Emperador rootstock can be purchased from Log House Plants, Plug Connections, and Territorial Seed Company. Currently, none of these sources offer plants grafted onto Fortamino or DRO141TX. Farmers can inexpensively produce grafted plants, however grafting techniques may require practice before grafting success.
For more information on how to graft tomatoes, see the Introduction to Grafting Manual. Fortamino is available as organic seed from High Mowing Seed Company and DRO141TX (not available as organic seed) is available from Johnny’s Selected Seeds.
Resources:
Kubota, C., C. Miles, and X. Zhao, 2016. Manual: How to produce grafted vegetable plants. Available at http://www.vegetablegrafting.org/resources/graftingmanual/
Stone and Davis, 2021. OSU dry-farmed tomato project reports. Available at https://horticulture. oregonstate.edu/article/dry-farm-tomato-production.