There has been an increased interest in grafted vegetables. In particular, much work has been done with tomatoes and watermelons on grafting. There are two main reasons for using grafted plants: 1.) to manage soil-borne diseases and 2.) to increase plant productivity by providing a more vigorous root system
In grafting, a rootstock plant compatible with the crop with desired disease resistance and/or vigor traits is selected and the desired crop is used as the scion to graft onto the rootstock. Both rootstock and the desired variety are grown to the right stage (small seedling), are grafted, and then are placed in a healing chamber for a period of time. There are 4 basic types of grafts – splice (or tube), side, approach, and hole insertion. The splice or tube graft is usually used for larger grafting numbers (scion is cut at an angle just above he cotyledon, is removed entirely, and is then attached with a grafting clip or tube to the rootstock which has had the top cut off at a complimentary angle). The approach graft where both plants are placed side by side and then grafted together while still attached to root systems is commonly used by beginners because of greater chance of success and limited need for a healing chamber.
With tomatoes rootstocks used are either tomato hybrids or hybrids between tomatoes and wild relatives to tomato (called interspecific hybrids). Interspecific rootstocks are often more vigorous. In addition, wild eggplant species and eggplant interspecifics have been used for tomato rootstocks. The following are some available rootstocks and the companies that they are available from:
- BHN Seeds: BHN 1054, BHN 998
- D. Palmer Seed: RST-04-106, RST-04-107, RST-04-112P, RST-04-113
- Rijk Zwaan: Big power
- Seminis Seeds: Cheong Gang, Shin Cheong Gang
- American Takii: Achilles-M, Aegis, Aloha, Anchor-T, Armada, B.B., Camel, Helper-M, Survivor
- De Ruiter Seeds: Beaufort, Maxifort, Mutlifort
- Enza Zaden: Efialto
- Hazera Seeds: Resister, Vigostar 09, Resiguard
- Nunhems Seeds: NUN0003, NUN0004, NUN0005, Spirit
- Sakata Seed America: TMAA804, TMZQ702, TMZV802, TMZV803
- Syngenta Seeds: TX301, Strong Foot
- Western Seed: Monstro, Titron
When you choose rootstocks for tomato, you will select for resistance to soil-borne diseases of concern such as Verticillium, Fusarium, Bacterial Wilt, or Root Knot Nematodes. In addition to the rootstock’s resistances, you need to select the rootstock based on the expected level of vigor, relative to your scion. If scion is a less vigorous variety and if a very vigorous rootstock is used, adding vigor to the scion is expected. However, if rootstock is too vigorous relative to scion, you may experience overly vegetative growth of your tomato plants, potentially reducing yields. Some rootstocks can achieve higher yields even without disease present in the root zone.
Watermelon are commonly grafted onto interspecific hybrid squash (Cucurbita maxima x Cucurbita moschata) or bottle gourd (Lagenaria siceraria). These will have Fusarium wilt resistance. Some interspecific hybrid squash rootstocks have chilling tolerance in addition to the disease resistance, but some rootstocks may be vigorous and could delay flowering if fertilization is not managed properly or reduce sugar content (Brix); bottle gourd rootstocks have chilling tolerance and less vigor then squash rootstocks, having little effects on fruit quality or flowering. These rootstocks are not root knot nematode resistant. Work at the USDA in Charleston, SC has identified some wild watermelon rootstocks with root knot resistance and these may be available as rootstocks in the future. The most common rootstocks used for watermelons are Strong Tosa (an interspecific Cucurbita cross) and Emphasis (a bottle gourd).
For Delmarva, grafted watermelon plants have been trialed for Fusarium wilt resistance and grafted tomato plants have been used for bacterial wilt resistance (Eastern shore VA). Grafted tomato plants are also available from some transplant growers in the region and have been trialed by some tomato growers. Grafted tomatoes may be very useful for growing heirloom types, which have limited soil-borne disease resistance.
Much of the information in this article was taken from the vegetable grafting website at the University of Arizona: http://cals.arizona.edu/grafting/ .
A good pictorial guide to watermelon grafting can be found at the University of Florida: http://edis.ifas.ufl.edu/pdffiles/HS/HS33000.pdf .
Source: University of Delaware, Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu