Final report for OW23-377
Project Information
The project goal was to develop propagation methods and nursery production practices for a new monopodial rootstock (Vaccinum arboreum L.) developed by the North Willamette Research and Extension Center of the Oregon State University. Working with two commercial tissue cultural labs and a production nursery in Oregon, we have successfully established tissue culture methods to produce stage I, stage II, stage III, and a liner production cycle for the new rootstock. More than 73% rooting rate was achieved from stage II to stage III plants. The nursery growing techniques, optimum nitrogen, and media pH levels were determined. The goal of grafting clonally produced rootstock plants was accomplished in the production nursery. A nursery production cycle was successfully developed for the rootstock commercialization. Two producers in the project have pending sales of the rootstock using newly developed propagation methods. The outcome of this research has been communicated to targeted nursery growers via workshops, presentations, and publications. The funding also helped the submission of a plant utility patent to the USDA. A survey of targeted potential nurseries indicated most of them have interests to commercially adopt the nursery practices developed and are willing to produce grafted blueberry plants from growing the rootstock to grafting, and sales of the blueberry trees.
- Improving the efficiency of producing stage II tissue culture Vaccinium arboreum plantlets (Producer one).
- Enhance the rooting percentage of Vaccinium arboreum plantlets (Producer two).
- Growing blueberry rootstock (V. arboreum) plants (Principle investigator and producer three).
- Grafting blueberry cultivars onto the blueberry rootstock to produce blueberry trees (Principle investigator and producer three).
- Disseminate information to nursery growers on how to grow the V. arboreum rootstock and use grafting to produce blueberry trees (Principle investigator).
The proposed project lasted 23 months. Major research activities are illustrated in the following Gantt chart. The milestone for each research objective is reflected by the end of data collection and statistical analyses described in the research plan section.
Gantt chart – Research activities to accomplish stated objectives 1-5.
Gatt chart project timelineGatt chart final
Cooperators
- - Producer
Research
Research facilities and major instrumentation and equipment
Microplant Nurseries and North American Plants, LLC are commercial tissue culture labs. They are well equipped to conduct research and develop experiments for new plant materials.
North Willamette Research and Extension Center (NWREC) has plant growing facilities certified as an operational nursery. The NWREC has a climate-controlled greenhouse, several hoop houses, container growing pads, various moisture and EC sensors, LI-COR from the nursery program, and general computer and software for statistical analysis.
Plant materials: Unrooted tissue-cultured plantlets of V. arboreum rootstock were produced by Microplant Nurseries Inc. The V. arboreum rootstock in 1” plug liners were received from North American Plants, LLC (NAP) in July 2023. More rooted 1" plug liners were obtained from NAP in spring of 2024 for the potted experiment at the NWREC.
Growing conditions and substrate: The NWREC’s greenhouse can regulate temperature, humidity, light, and provide bottom heat. Outdoor growing facilities include standard landscape fabric covered pads with micro-spray irrigation. The fertigation and overhead micro-spray irrigation systems were available for water and nutrient management. A self-built acid delivery system was used to control the media pH at both low and high levels. The rootstocks were grown in 1 gal size containers using a commercial nursery growing mix of bark, peat, and perlite.
Nutrient solutions: We used fertigation to deliver various nutrient treatments to the 1 gal size containers. The nutrient solution was based on published studies of growing tissue culture blueberry plants in pots (Yang et al., 1997) except varying nitrogen amount as the main treatment. The nutrient recipe consists of (in mM) 0.3 P, 1.0 K, 1.0 Mg, 0.5 Ca, 2.8 S, and (in uM) 89.5 Fe (as EDDHA), 34.2 B, 10.0 Mn, 1.0 Zn, 0.01 Cu, and 0.02 Mo.
Treatments: A 3x2 factorial experiment with three nitrogen concentrations (low, medium, and high at 1 mM, 2.5 mM, and 5 mM respectively) and two pH levels (normal and high at 4.5 and 6.2 respectively). The source of nitrogen used was ammonium sulfate and delivered weekly to containers via drip irrigation and controlled by a Dosatron pump. Based on commercial practices of substrate blueberry production, we kept monitoring the electric conductivity (EC) in the effluent and maintain it at 0.8 ds/m (see experiment photo).
Experiment 1. Investigate the effect of in vitro medium pH on shootlet production.
Location: Microplant Nurseries
In our previous collaboration with Microplant Nurseries in winter 2019, a tissue culture protocol for the blueberry rootstock using axillary buds was established. Follow the same protocol, the young developing buds from dormant excised shoots from a V. arboreum plant selected and evaluated at the NWREC were forced by using a Floralife solution in the greenhouse. A woody plant medium (WPM) was used with various plant growth hormone combinations (no details due to proprietary information) for axillary bud proliferation in vitro. Based on a recent in vitro propagation study of V. arboreum (Li et al., 2021), the pH of tissue culture medium affected the rate of shoot proliferation. In our experiment, the media pH was adjusted to the optimum level of 5.75. The light and growing conditions were the same for all tissue culture jars placed on the same culture bench. After two months of growth, the number and the length of shootlets in each jar were recorded.
Experiment 2 Effect of IBA dipping on rooting percentage of V. arboreum rootstock.
Location: North American Plants LLC
In spring 2023, more than 1500 micro-propagated shootlets from experiment 1 (1.5”-2” tall shootlets) were rooted under a climate controlled hoop house. The shootlets from Microplant were grown in 1” liners filled with peat and perlite prepared in house at the NAP. They were evenly divided into two groups. The original plan was to have one group of shootlets treated with 1 g L−1 indole-3-butyric acid (IBA) by dipping the cutting into the IBA solution, while the other group not treated as an experiment control. This plan was modified to have both groups treated the same without a control because a study had showed the effectiveness IBA treatment for rooting in V. arboreum plants. These plants were placed under a misting system which delivers irrigation and nutrients, and controls relative humidity in the hoop house for four- months of growth. The rooted shootlets were transported to the North Willamette Research Extension Center, where the Agricultural Technical Advisor (W. Yang)and his research assistant evaluated the rooting percentage of TC shootlets.
Experiment 3. Determine the optimum nutritional needs of V. arboreum rootstock.
Location: NWREC and J. Frank Schmidt and Son, Co
In July 2023, a total of 180 V. arboreum plants were transplanted into 1-gallon size containers and placed on nursery fabric beds in the NWREC cravo under a semi enclosed structure. These plants were cared for based on established protocols previously. However, due to the late potting time, the growth of these plants was unsatisfactory. To solve this problem, we repotted new rootstock plants received from NAP in spring 2024. For each nitrogen and pH combination treatment, 36 plants were grouped as one replication with 5 replications arranged in a randomized block design. The container moisture and EC were monitored throughout the experiment. The amount of water supplied for irrigation were based on a water balance method to supplement daily plant evapotranspiration plus moisture loss from the container. During a 3-month growing period, plant height and diameter were measured weekly beginning after week 3 of potting up the experiment. The effect of nitrogen and pH levels on the growth differences were determined.
At JFSS nursery, more than 1000 rooted rootstock plants were received from NAP in July 2023. These plants were grown in a high humidity environment for four month, then allowed to go dormant outside under the nursery hoop house. They were staked in spring 2024 and grew in a bark nursery bed until dormancy in 2024. These plants were used for the grafting experiment at JFSS facility.
Experiment 4. Determine the percentage of graft take.
Location: JFSS hoop house
More than 500 V. arboreum rootstock plants from Experiment 3 at JFSS nursery were planted in a bark nursery bed (Fig 1) since spring 2024. In early March 2025, more than 200 plants were grafted with dormant scion wood taken from 'Legacy' blueberries. Side grafting technique was used with a grafting height at 24”. The choice of 'Legacy' as the scion wood was due to the popularity of this cultivar for home gardens. For each dormant scion wood, at least two to three vegetative buds were visible after the grafting union was wrapped with grafting tape. All grafted plants were kept in the nursery beds to allow continued grafting union development at the JFSS nursery. Data taken included the percentage of grafting success, indicated by the new growth coming out the dormant scion wood.
Data analyses
All experiment data were statistically analyzed by using SAS statistical software (Gary, NC USA).
Working with Producer One (Microplant Nurseries Inc.), we successfully achieved Objective One by producing over 1500 stage II tissue-cultured (TC) Vaccinium arboreum plants at the Microplant facility from dormant shoots of field-grown V. arboreum plants. The results were impressive, with each tissue culture jar yielding 30-50 shootlets. Building on this initial success, Microplant Nurseries has begun commercially producing 10,000 stage II V. arboreum shootlets using the established TC methods for a large Oregon blueberry company in December 2024. The beginning of commercial rootstock production went beyond the initial scope set for Microplant Nurseries Inc. for this grant.
After receiving 10 trays of 144-cell rootstock plants from NAP, these plants were sorted, and checked for root system health. The average rooting rate exceeded 73%, with some shootlets failing to root and subsequently wilting in a few days. NAP expressed satisfaction with the rooting results, confirming the successful completion of Objective Two. In March 2025, NAP has begun to deliver more than 700 V. arboreum stage III TC plants to a commercial blueberry nursery for the production of grafted blueberry plants.
For Objective three, Producer three (J. Frank Schmidt and Son, Co. - JFSS) received rooted plantlets from NAP in late June 2023. These rooted plantlets were grown in 4-inch pots with a commercial maple growing substrate. After more than three months’ growth in the high humidity growing house, the tallest plants reached more than 14 inch in height. The growth rate was impressive under the JFSS growing facility. These plants were moved to the section of the greenhouse without bottom heat to undergo overwintering and through the spring. Then they were planted on nursery bark beds under hoop house to increase their caliper size during the 2024 growing season. JFSS has successfully established the nursery production cycle for producing grafted blueberry plants. For example, it takes a minimum of 24 month to grow the caliper size needed for producing grafted blueberry plants. A detailed nursery production cycle is described in Table 1, which is a significant accomplishment for the three producers involved in the grant, which exceeded the original research goals. The production cycle will be used for planning of nursery production, marketing, and sales of grafted blueberry plants in the future.
Table 1. Production cycle for the blueberry rootstock
In the nutrition and pH experiment conducted at the NWREC, we found that media pH did not affect the final plant height and trunk diameter for grafting needs, indicating these rootstock plants are adaptable to high pH soils (Table 2 and Table 3). Nitrogen levels had a significant effect on plant height but not on trunk diameter (Table 3). A media nitrogen level of 2.5 mM supplied to plants throughout the three months summer growth was the best rate for producing the tallest plants. Plants received high nitrogen level of 5.0 mM seem to have the largest trunk diameter numerically, but did not show statistical difference. These findings have been shared with the three Producers and other potential nursery growers.
Table 2. Rootstock height affected by media pH and nitrogen application rate.
Table 3. Rootstock diameter affected by meida pH and nitrogen applicatino rate.
For Objective four, the grafting has been completed; however to evaluate the success of grating rate, we need to wait for the longest new shoot from the scion wood reaches more than 4 inches in length, which may take another two to three weeks into April 2025 for a final evaluation. The delay was due to weather factors and the number of available plants with desirable grafting diameters.
Research Outcomes
The successful tissue culture production of Stage I and Stage II shootlets from Producer 1, the acceptable rooting rate of Vaccinium arboreum from Producer 2, and the excellent growth of V. arboreum plants in the nursery facility of Producer 3 provided valuable knowledge for scaling up the new blueberry rootstock production for grafting and blueberry tree cultivation. A complete nursery production cycle for the new rootstock was established. The Principle Investigator has also developed new research relationships with the University of Nevada for water use efficiency research.
Oregon State University's Licensing and Intellectual Property office filed a plant utility patent. The first commercial sale of 10,000 new rootstock plants to a major blueberry company in Oregon has begun, involving Producers 1 and 2. Producer 3 has integrated the new rootstock into its research and development plan.
We aim to promote wider adoption of rootstock production practices and nursery-based blueberry tree grafting using this new rootstock. In response to labor costs and climate challenges in blueberry cultivation and harvesting, the new rootstock introduces a more efficient production system. It reduces organic matter input, lowers soil acidification costs, improves weed control, enhances water-use efficiency, and significantly increases machine harvesting efficiency by minimizing fruit loss. This blueberry tree production system will enhance the resilience, sustainability, and competitiveness of the U.S. blueberry industry. Scientifically, the new blueberry rootstock offers scientists a new blueberry science frontier to study rootstock and scion interactions in blueberries, and how to use rootstocks to develop efficient production systems.
Education and Outreach
Participation Summary:
In 2023 and 2024, 8 blueberry educational workshops were conducted at the NWREC including machine harvesting, blueberry nutrition, and blueberry pruning workshops. In these workshops, we introduced the concept of blueberry canopy management and ways to reduce ground loss of fruits, including the potential of using rootstocks plants for producing grafted blueberries. During the Oregon blueberry field days, Yang showed blueberry grower and nurseryman of the nutrition experiment. Yang also gave two presentations on the funded project to a group of nursery professionals touring the NWREC. Yang participated in the WSARE’s BPASS and gave a presentation about the funded project. A summary of the activities is listed in Table 4 and a timeline (Planned vs completed) is listed in Table 5 and Table 6. A final nursery grower survey was also conducted to understand the opportunities and challenges for adopting the rootstock. The survey results are listed in Table 7 below, showing that the majority of nursery producers are willing to adopt the new blueberry rootstock.
Table 4. Summary of educational activities
|
Date |
Activities |
Number of attendees |
Who |
|
May 2023&2024 |
OSU Blueberry machine harvest Workshop |
69 |
Growers, harvester companies |
|
July 2023&2024 |
OSU Blueberry field day |
220 |
Growers, nurserymen |
|
October 2023&2024 |
Blueberry nutrition workshop |
50 |
Growers |
|
December 2023&2024 |
Blueberry pruning workshop- field demonstration teaching |
57 |
Growers, pruning company |
|
December 2023&2024 |
Blueberry pruning workshop-classroom teaching |
57 |
Growers, pruning company |
Table 5. A list of planned education and outreach activities.
Table 6. A list of completed education and outreach activities*.
|
|
2023 |
2024 |
|||||
|
Activities |
Apr-Jun |
Jul-Sep |
Oct-Dec |
Jan-Mar |
Apr-Jun |
Jul-Sep |
Oct-Dec |
|
a. Stakeholder workshops |
Done |
|
|
|
|
|
Done |
|
b. Stakeholder training workshops |
|
|
|
|
|
|
Done |
|
c. Conferences |
|
|
|
Done |
|
Pending |
|
|
Obj#2-Stakeholder field days |
|
Done |
Done |
|
|
|
Done |
|
Obj#3-Popular publications |
Done |
|
|
|
|
|
Done |
|
Obj#4-Educational video |
|
|
|
|
|
|
Pending |
|
Obj#5-Extension and peer-reviewed publications |
|
|
|
|
|
|
Pending |
*OSU’s Licensing and Intellectual Property Office required the Agricultural Technical Advisor (Dr. Yang) to complete the patent application of the experimental rootstock used in this project. As a result, some education and outreach activities (1 conference presentation, a grafting video, and an extension production guide) were delayed due to concerns of Public Disclosure which may lead to the loss of patent rights. This issue was resolved as OSU’s IP office filed a plant utility patent for the new rootstock in July 2024. The conference presentation at the Northwest Ag Show will be in August 2025. The remaining grafting video and extension production guide will be completed by May 2025 once the grafting rate is determined in April 2025.
Table 7. A nursery grower survey about rootstock adoption and challenges.
|
Survey questions |
Answers |
|
Likelihood of adopting a new rootstock |
94% indicated willingness to adopt |
|
Challenges of introducing a new plant to business |
90% indicated customer demand |
|
Technical support to grow a new plant |
100% indicated support needed |
|
Particular concerns for adopting a new plant |
60% indicated marketing |
|
Interests in producing the blueberry tree from start to finish (full production cycle) |
85% indicated full cycle production |
|
Additional feedback on this new rootstock |
60% indicated excited and willing to try |
The workshops we conducted were a combination of classroom teaching and in field hands-on demonstrations. We surveyed the attendees after some educational events (Nutrition and pruning workshops) and have the following findings. For our pruning workshop, there were estimated 25% participants of professional Spanish-speaking farm worker. The findings on knowledge gains and possible adoptions indicated effectiveness of our workshops (Table 3).
Table 3. Measurements of knowledge gains and probability of adoption recommended practices
|
Workshops |
Knowledge gains z |
Likelihood of adoption recommended practices y |
|
Pruning (Classroom) |
70% |
2.9 |
|
Pruning (Field demo) |
54% |
2.9 |
|
Nutrition |
36% |
2.8 |
Z Likert scale rating of 1 = poor, 6= excellent; y Likert scale rating of 1 = least likely, 3= most likely.
Education and Outreach Outcomes
It is still early in the project to make recommendations for education and outreach for the nursery production of blueberry trees. However, pruning practices regarding using the grafted blueberries have been discussed in two workshop. Other possible outreach activities will be inviting nursery growers to learn grafting practices when the blueberry trees are produced. Learning nutritional needs of blueberry plants are also important topics to ensure the success of growing healthy grafted blueberry plants. Based on the final grower's survey, specific recommendations for nursery grower education may include workshops and hands-on training.
Grafting demonstrations & training – Organize hands-on workshops where nursery growers can practice grafting techniques and receive expert guidance. Consider recording these sessions for online video access.
Rootstock cultivation best practices – Offer targeted training on selecting, growing, and maintaining healthy rootstock to improve the success rate of grafted blueberry trees.
Pruning techniques for grafted blueberries – Continue expanding workshops on pruning, focusing on optimizing fruit production and plant health.
There were two key areas which increased the knowledge of farmers: one is the understanding of blueberry pruning practices in canopy management which including the use of blueberry trees; the other is the understanding of blueberry nutrition which is critical to cultivating grafted plants.