University of Central Florida Undergraduate Research Journal - Creating a Multi-Berry Shrub via Cross Grafting
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Creating a Multi-Berry Shrub via Cross Grafting

By: Alexa Laurent | Mentor: Dr. Rani Vajravelu

Discussion

The results of this experiment supported our initial hypothesis.  There was a higher success rate among the rootstock with a hardier stem.  The r. fruiticosus shrubs had a less sturdy stem (Figure 5) compared to the r. idaeus stems (Figure 6).

Figure 5: Raspberry stem. Photo credit Chelsea Schuler

Figure 6: Blackberry stem. Photo credit Chelsea Schuler

The stems of r. fruiticosus did not bend easily and were darker in color.  The shoots of r. idaeus were able to bend and contort as needed to reach upward to the sunlight and competed among themselves for resources.  The stronger base on the sturdier r. fruiticosus showed signs of being able to support the scion to a higher degree, allowing a better chance for the tissues to fuse and nutrients to be passed to the scion.  The r. fruiticosus plants could have also supported the graft, as they had been in a state or dormancy during the experiment.  The dormancy state allows for less competition for the plant’s resources during the healing stage, as the plant is conserving energy and not looking to optimize energy usage for growth at that time.

While the r. idaeus were also dormant at the beginning of the experiment, they exhibited a more opportunistic approach to their growth once they exited their dormancy stage.  This growth style may have contributed to the grafts’ failure to heal.  Another factor that could contribute to a lower grafting success rate is when a plant drops branches that are injured, as is the case with r. idaeus; when a branch is deemed too costly by the r. idaeus shrub, it is quick to drop the branch.  This mechanism is similar to how plants adapt when under stress or in difficult conditions (Gruntman, 2017).  Plants, when in conditions that are harsh for growth, will adapt and redirect their energies toward growth types and features that suit the environment.  This adaptation is seen in plants that grow in the shade of taller plants; they either adapt to growing in the shade or expend their energy on vertical growth (Gruntman, 2017; Bechtold, 2018).  The r. idaeus plants grow multiple shoots at any given time, so they could have found that trying to heal the graft took more energy than growing a new shoot, and thus directed their energy to the most beneficial exploit (Karban, 2018).

While the lack of tissue growth over the union site could have been caused by the plant’s decision, it could also have been caused by the scion being covered by the taller, uninjured r. idaeus branches, and thus being deprived of sunlight.  Lack of sunlight can cause a plant to not be able to grow, hindering its development, and sometimes leading to death (Bechtold, 2018).  Being hindered by taller shoots could have also contributed to the plant interpreting the branch as unbeneficial or caused the scion to not receive enough nutrients before it fully connected to the rootstock. 

Another possibility is that the wood glue could have seeped into the plant’s internal tissue, covering the vessels needed to transport nutrients to the scion and preventing healing from occurring (Bechtold, 2018; Kerr, 2019).  Further study into grafting on a r. idaeus rootstock and altering variables such as the grafting method, pruning plants during the healing phase, or adding nutrients to the soil may show if there is a change in the success rate.

As of now, further study into how different care methods can affect grafting success rates could further our understanding of this method and assist in making grafting more accessible to growers.  This experiment used common household tools to see if grafting could be affected by the quality of materials used.  In this instance, it is unclear if the wood glue affected the healing process of the graft, but the electrical tape was successful at keeping moisture from entering the wound.  This method assists in making grafting more accessible to the public, such as Florida growers in an urban environment or arboretums at universities.  In the city, there is not much green space and being able to optimize that greenspace while using easily-accessible materials can increase plant productivity and improve available resources.  Grafting using common tools can also allow students to study grafting and to contribute to their community while going to school. 

Although there are multiple grafting methods, this study chose to use cleft grafting to test the use of household items to graft an older plant (instead of a seedling) to have a better example of each plant’s individual physiology.  The study of the effect of plant physiology on grafting will be furthered by testing the use of household items versus grafting tools, cleft grafting versus grafting clip.  We will also test to see if the age of the plant affects the plants’ physiological effect on the process by testing seedlings and adult plants.

Overall, this study has shown that the rootstock, the grafting method, and the healing process can be affected by the type of rootstock used, which in turn, causes an effect on the success rate of the grafting procedure.  With this result in mind our future studies will focus on narrowing down the extent that plant physiology affects the healing rate of grafting and if it is possible for the plant physiology to affect more than just the healing rate.  Current research shows that grafting is only possible between related plants no matter the physiology. How closely related do the plants have to be is a question that can be further tested.

Acknowledgements >>