Reducing Farmer Risk through the Use of Triploid Hemp Genetics

Progress report for LNE21-430R

Project Type: Research Only
Funds awarded in 2021: $101,168.00
Projected End Date: 05/31/2024
Grant Recipient: University of Connecticut
Region: Northeast
State: Connecticut
Project Leader:
Dr. Jessica Lubell
University of Connecticut
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Project Information

Summary:

Hemp is a new and profitable crop for cannabinoids. Hemp is a diploid, dioecious species, and female plants are desired, since their inflorescences produce the greatest quantity of cannabinoids. When female plants are pollinated, they set seed, which significantly reduces cannabinoid yield. Despite farmers best efforts to remove male plants from their fields, crops remain susceptible to pollen drifting from neighboring farms or feral plants. One way to eliminate seed set is to develop triploid hemp, which produce gametes with imbalanced chromosomes that are non-viable. There are many horticultural examples of triploids that are sterile including watermelon, banana, citrus, and hops. My lab developed triploid hemp plants and it needs to be demonstrated that triploids will not set seed, maintain high cannabinoid content, and that their horticultural production potential is sufficient to allow farmers to successfully grow the crop. This project will compare triploid plants to standard diploid plants both in the greenhouse and the field. In the greenhouse, controlled pollination studies using genetically male pollen will test plant sterility. Plant performance and cannabinoid production will also be evaluated. In the field, horticultural performance, cannabinoid production and ability to resist pollen under real world conditions will be evaluated. Many northeast farmers have completely lost their hemp crop due to inadvertent pollination by plants found in the wild or on nearby farms. If triploid hemp proves to be seedless, then it will enable farmers to grow high cannabinoid yielding hemp without risk of crop loss due to pollination and seed set. In a recent survey of 28 farmers and extension specialists, all respondents were extremely supportive of university research to evaluate the sterility and growth performance of triploid hemp. As part of the process of fully vetting the sterility of triploid hemp, a research farmer will test plants in their annual variety trials. Farmers will participate in annual on-site demonstration events where they may view research plants, receive preliminary research results, and provide feedback on the project.  

Project Objective:

Evaluate the sterility and growth performance of triploid hemp plants developed through breeding. Greenhouse and field studies will be conducted to confirm that triploid hemp is infertile or exhibits reduced fertility. Sterile triploids would allow northeast farmers to grow hemp without the risk of seed set reducing cannabidiol (CBD) yield or hemp escaping cultivation to the wild. In addition to sterility, triploid hemp will likely possess greater yield and CBD content. Adoption of seedless triploid hemp would improve sustainability and profitability for northeast hemp farmers.

Research

Materials and methods:

2021

A field study to evaluate sterility of four triploid genotypes and one diploid genotype (control) was installed in June 2021. However, this planting perished because of extreme rainfall (that more than doubled the historic average) and flooding in summer 2021 in Connecticut and other parts of the northeast due to four storms that that came up the East Coast.

A greenhouse trial was conducted to evaluate the sterility of two triploid female genotypes of the strain Wife compared to a diploid female genotype of the strain Wife (control). Plants of each genotype were clonally propagated by stem cuttings for this study. Plants were grown in a climate-controlled greenhouse under 18 hr photoperiod (vegetatively) for 2 weeks, after which the photoperiod was adjusted to 12 hr (to induce flowering) for an additional 9 weeks. Plants were grown in trade number 2 nursery containers filled with a peat moss-based potting mix. Plants were top-dressed with 15N– 3.9P–10K controlled-release fertilizer (Osmocote Plus 5- to 6-month formulation) at 30 g per container. Plants received a soluble fertilizer providing 100 ppm nitrogen (N) at every irrigation, which occurred as needed. At peak flowering plants were hand pollinated (at 12 shoots per plant) with pollen from genetically male cannabis plants. A paint brush was used to deliver a heavy sprinkling of pollen to each shoot. The male plants were cultivated in the same greenhouse section as the female study plants. Since the male plants produced copious quantities of pollen, it is reasonable to assume that in addition to hand pollination, natural pollination occurred to a great extent. Study plants were arranged in a randomized complete block design with 11 replications. The experimental unit was a single potted plant. At the end of the study, plants were harvested and all seed collected per plant. For the triploid genotypes seed was hand counted. For the diploid control plants the total seed per plant was calculated using the weight of a quantified subsample of seed. The number of viable (brown), unviable (white/tan), and irregular shaped unviable seed was counted for every triploid plant and for a subsample of seed per diploid plant. Unviable seeds were hollow inside, which was confirmed by cutting the seeds open. Seed caliper was measured for 10 viable seeds per plant. Percent CBD and THC based on HPLC analysis was determined. Seed germination percent was measured for 15 viable seeds collected per study genotype. Flow cytometry analysis was conducted for 20 seed collected from triploid plants to determine their ploidy.

 

Research results and discussion:

2021 Greenhouse Sterility Study

Diploid plants produced 3000 seed per plant and triploid plants produced 100 seed per plant. Of the seeds produced, 89% were viable for diploids and only 9% were viable for triploids. Of the seeds produced by triploid genotypes, 52% to 60% were irregular in shape and unviable, while only 2% were irregular for the diploid control. Triploid seed germinated at only 13% to 53% and out of 20 seed tested by flow cytometry, 19 were diploid and one was triploid. All seed tested from diploids were diploid.  We can conclude that the triploid genotypes evaluated had significantly reduced fertility and are highly resistant to pollen, since they produced only 0.3% viable seed compared to the diploid control.

Participation Summary

Education & Outreach Activities and Participation Summary

Educational activities:

1 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

90 Farmers
29 Number of agricultural educator or service providers reached through education and outreach activities
Outreach description:

2021

On December 9, 2021, a virtual field day was conducted, which included two separate educational presentations. After each presentation there was a lengthy and dynamic discussion with attendees about the project and results of the research to date. There were 20 attendees of which 15 were farmers or in industry, and 5 were extension educators. The advisory group for this project, consisting of 3 growers and 3 extension educators, attended this event and participated in the discussions.

I provided a presentation about this project for the 2nd Annual Hemp Science & Technology Virtual Symposium, which aired on December 1, 2021. There were 360 registered for the event and 99 attended the session live. The session was made available to registrants to watch for one year.

Learning Outcomes

9 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

2021

After the virtual field day on December 9, 2021, an online survey was disseminated to attendees to gauge learning outcomes. The survey was anonymous and did not distinguish farmers from extension educators. There were 20 attendees and 9 of them responded to the survey. The key areas in which farmers reported changes in knowledge were: (1) what is triploid hemp, (2) how is triploid hemp seed produced, and (3) triploid hemp sterility in the greenhouse. For each key area, respondents were asked to rate their level of understanding before and after the meeting on a scale of 0 to 5 with 0 = no understanding and 5 = great understanding. Respondents' knowledge of key area 1 increased from 3.6 before the event to 4.9 after the event. For key areas 2 and 3, respondents' knowledge increased form 3.0 before the event to 4.8 after the event.

Project Outcomes

2 Grants applied for that built upon this project
1 New working collaboration
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.