Rising Interest In Grafting

As many know, most vegetable grafting in the U.S. is done by hand, as manual processes have proven to be appropriate for many situations. Automated grafting, however, is on the rise in other parts of the world. When will the U.S. adopt the technology?
To get an answer to that question and to find out about the latest in manual grafting, automation, and the future of grafting in the U.S., American Vegetable Grower had a chance to talk with grafting researcher Chieri Kubota, a professor in the School of Plant Sciences and Department of Agricultural and Biosystems Engineering at the University of Arizona. Find out what she has to say about the state of the industry and what she sees as necessary to move it forward.

Q1 What are the latest developments in manual grafting for vegetable crops? What is being done to increase manual grafting speed?

Kubota: If you look at the past 20 to 30 years, the biggest improvement happened in the early 1990s when tube grafting for tomatoes was developed by a scientist in Japan. This is the system where you cut the scion and the rootstock at a sharp angle and then hold the grafted union using a plastic tube. A Japanese Extension article was published about this technology that indicated it improved grafting speed three times compared with the older technology called approach grafting. Today, this technology — tube grafting — is used by virtually all growers worldwide, including North America.

It is important to note, though, that most of the grafting propagators are outside of the U.S., and they are grafting tens of millions of plants every year. Nearly 10 million grafted plants are annually imported by greenhouse growers in the U.S. from Canada. This is still a very small number compared to other countries in Asia or Europe that use grafting more extensively. For example, Japan is grafting about 450 million plants per year and their largest propagator is grafting 12 to 15 million plants each year.

Q2 What are the latest developments in automation? How have things changed since the first commercial model of a grafting robot was created in 1993?

Kubota: In the 1980s and 1990s, the Japanese government promoted technology in horticulture by putting a lot of money into research and development. One application was to create grafting robots. Several models were launched during that time period.
Since then, many grafting robots were also developed outside of Japan. Korea developed some in the early 2000s that are what we call semi-automated robots. Specifically, there are two types of robots: fully automated and semi-automated. For the semi-automated ones, someone has to feed the plants to the machine. For fully automated units, a person can place a tray of 100 or 200 plants into the machine, and the machine takes the plants and grafts them.

In 2006, a fully automated machine was developed in the Netherlands for grafting tomatoes. Unlike semi-automated ones, all that is necessary is to have one person provide rootstock and scion trays. In 2010, the Dutch company started developing the second-generation machine, with improved operation and speed (greater than 1,000 grafts per
hour) using a grafting clip widely used by the nursery industry. The company is currently testing the machines for large-scale grafting operations.

A fully automated machine was also developed for cucurbits (melons and cucumbers) in Japan in 2011, as an upgraded version of the semi-automated robot developed in 1990s.
There are other robots, both semiautomatic and fully automatic, in Spain, Taiwan, and Italy that are under development.

Q3 What is currently being done in the area of automation for vegetable grafting in the U.S.? When do you think automation will become more prevalent in the U.S.?

Kubota: There is some work going on in Florida, a researcher there is interested in developing automated grafting equipment. To me, it is just a matter of time.

We recognize increasing interest to introduce grafted plants for open field production, so the demand is going to increase and growers will begin grafting in U.S. nurseries.

When you develop an automatic system, you also have to take into consideration what kind of trays will be used, the plant species, the expected size of plants, and the substrate type. For example, the Dutch system uses a rockwool substrate and that won’t be suitable for U.S. open-field production. So when developing a grafting robot, you have to target certain applications because the robot needs strict specifications. In addition, horticultural trays for nurseries are available in many different sizes and items such as grafting clips and razor blades must be widely available in the U.S. This is another reason we need U.S.-based technology development for this particular area.

Plus, the way the plant is grafted impacts how it can be managed in the field. For example, a grafting method that potentially increases the chance of inducing shoot growth from the rootstock may be manageable in small farms in Asia or Europe, but will be a serious problem in large U.S. operations. A USDA researcher in Florida, Michael Bausher, is looking at this issue to address in our on-going USDA Specialty Crop Research Initiative project. Bausher and another researcher, Richard Hassell in South Carolina, will be evaluating grafted plants’ performance in the field when grafted by machine. All these will help us better understand the issues and possibilities.

Q4 What are some key points on vegetable grafting you have learned from your research?

Kubota: My work focuses on propagation technology to increase the efficiency and to reduce the costs, which is why automation is under my watch. One of the things that is very important to make grafting successful is the uniformity of the seedlings. Machines can’t do the grafting unless there is some system or technology to make uniform plants. Uniformity in plant quality attributes increases grafting efficiency.
It is also important for a grafted union to be very strong to withstand windy open fields. Grafting methods, including automation, would impact the strength of the union.

Q5 Where do you think the U.S. vegetable grafting industry will be in 10 years?

Kubota: In 10 years I see more grafting used in the U.S., hopefully with effective use of grafting automation. It may be difficult to envision it as currently only a small amount of plants are grafted in the U.S. (most grafting is done in Mexico and Canada). For example, in Turkey there was no grafting several years ago and now almost all watermelon plants are grafted in that country. The change was within the last four or five years. That change could happen in the U.S., too.

For that to happen, though, automation is the key. Large operations will need to adopt the technology. Initially, grafting could start with high-end producers such as organic or high tunnel growers that will slowly get into the technology — maybe 20% to 30% even within a few years. For example, in some areas there is no option, other than grafting, to overcoming soil-borne disease and pests.

Although the number of grafted plants in the U.S. is low today, that could change in just a few years.