Some Q and As on Vegetable Grafting

Several have asked about grafted vegetables and what is the advantage. Grafting vegetables has been around for a number of years now and has had some success in greenhouse production primarily. It started in Asia and has spread to Europe, primarily where heavy cropping (high yields) and disease problems can build rapidly.

So here are some Q and A’s I grabbed from some sites to further explain it. It is not hard to do, easier than woody plants. The method I am most familiar with is using plastic tubing to hold the top and rootstock together until they grow together. Other methods are done as well.

For backyard gardeners it is mostly just for fun right now but you can buy grafted transplants for the home market.

In vegetable production in greenhouses, most of the damage from continuous cropping is caused by soil-borne diseases and nematodes. As a countermeasure to the damage caused by soil-bone diseases such as Fusarium wilt, bacterial wilt and nematodes, grafting of fruit-bearing vegetables is popular in Japan. Plants are grafted onto various rootstock species and varieties, by a range of grafting methods. Recently, the tube grafting method has been developed for plugs. This is popular in the manual grafting of tomato, eggplant and cucumber plants. Grafting robots and healing chambers have been developed, and are used in nurseries producing grafted plugs. Since grafting gives increased disease tolerance and vigor to crops, it will be useful in the low-input sustainable horticulture of the future.

Application of Grafting to Vegetable Production

The production of grafted plants first began in Japan and Korea in the late 1920s with watermelon grafted onto gourd rootstock. Eggplant was grafted onto scarlet eggplant in the 1950s. Since then, the area of fruit-bearing vegetables based on grafted plants has increased. The proportion of the area in Japan producing grafted watermelon, cucumber, melon, tomato and eggplant reached 57% of the total production area in 1980, and 59% in 1990

Objectives of Vegetable Grafting

The main objective of grafting is to avoid soil-borne diseases such as Fusarium wilt in Cucurbitaceae (Cucumber, melon etc.) and bacterial wilt in Solanaceae (tomato, pepper etc.).

Species and Varieties for Grafting

Inter-generic grafting is used in the production of many fruit-bearing vegetables, i.e. cucumber grafted on pumpkin, watermelon, on bottle gourd, melon on white gourd (also known as wax gourd). Inter-specific grafting (grafting on to a different species) is generally applied to eggplant. Scarlet eggplant and S. torvum Swartz are popular rootstock for eggplant production. A large number of varieties for rootstock have been bred and released for use by growers in Japan.

Grafting Methods for Different Types of Fruit-Bearing Vegetable

Tomato plants are mainly grafted by conventional cleft grafting. Tube grafting has recently been developed for vegetable seedlings grown by plug culture.

Cleft Grafting

The stem of the scion (at the fair-leaf stage), and the rootstock (at the four to five-leaf stage) are cut at right angles, each with 2-3 leaves remaining on the stem. The stem of the scion is cut in a wedge, and the tapered end fitted into a cleft cut in the end of the rootstock. The graft is then held firm with a plastic clip.

Tube Grafting

Tube grafting makes it possible to graft small plants grown in plug trays two or three times faster than the conventional method. The smaller the plants, the more plants can be fitted into healing chambers or acclimation rooms. For this reason, tube grafting is popular among Japanese seedling producers. The optimum growth stage for grafting varies according to the kind of plug tray used. Plants in small cells must be grafted at an earlier growth stage, and require tubes with a smaller inside diameter. First, the rootstock is cut at a slant. The scion is cut in the same way. Elastic tubes with a side-slit are placed onto the cut end of the rootstock. The cut ends of the scions are then inserted into the tube, splicing the cut surfaces of the scions and rootstock together.

Eggplant

Eggplant is grafted mainly by cleft or tube grafting. The growth rate differs according to the species of rootstock used. The number of days from sowing to grafting varies accordingly.

Cucumber

Tongue Approach Grafting

Slant-cut grafting is easy to do, and has recently become popular. This grafting method was developed for robotic grafting. It is important to remove the 1st leaf and lateral buds when a cotyledon of rootstock is cut on a slant.

Planting Watermelon

Cut grafting is popular for watermelon. A schematic diagram of cut grafting is shown.

Melon

Melon plants are mainly grafted by tongue approach grafting. Tongue approach grafting for melon is similar to that used for cucumber plants.

Healing and Acclimatization

Grafting should be carried out in a shady place sheltered from the wind, to avoid wilting of the grafted plants. Grafted plants are usually healed and acclimated in a plastic tunnel. The healing and acclimatization are very important for grafted plants to survive. The tunnel is covered with materials which provide shade and maintain inside humidity: silver/white cheese-cloth (outside) and transparent film (inside). During acclimatization, it is recommended to keep light levels at about 3 to 5 klx.

Before grafting:

• Expose the scion and rootstock to sunshine for two to three days;
• Withhold water from the plants to avoid spindly growth, and
• Make sure that the scions and rootstock have stems of a similar diameter.

After grafting, keeping the grafted plants at about 30°C and with more than 95% relative humidity for three days of healing promotes the survival ratio. Gradually, the relative humidity is then lowered and the light intensity increased. During healing and acclimatization, it is important to keep a constant air temperature in the tunnel, in order to maintain high humidity. If wilting is observed, foliar spraying of grafted plants with water is effective in helping them survive. The shading materials and films should be adjusted according to the daily weather, with more shade on a fine day.

Healing has also been mechanized. The survival ratio is consistently high when the newly developed healing chambers are used. Healing chambers in which the environment is artificially controlled are now being used by many nurseries which produce grafted plugs.

Adapted from http://www.agnet.org/library.php?func=view&style=type&id=20110803135029