Breeding and Evaluation of Butternut Squash Varieties for Southeast Organic Farms

Progress report for FS20-325

Project Type: Farmer/Rancher
Funds awarded in 2020: $19,846.00
Projected End Date: 09/30/2022
Grant Recipient: Common Wealth Seed Growers / Twin Oaks Seed Farm
Region: Southern
State: Virginia
Principal Investigator:
Edmund Frost
Common Wealth Seed Growers / Twin Oaks Seed Farm
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Project Information


Using selective breeding to address disease problems can be an extremely effective solution that causes none of the environmental and health dangers posed by chemical fungicides (which are unfortunately the current go-to for downy mildew (DM)). Moreover, eliminating or reducing need for chemical sprays saves farmers money and improves feasibility of Southeast production. DM in cucumbers was effectively controlled for many years by the use of resistant varieties. We aim to do the same with butternut squash, and whats more we aim to develop and utilize diverse sources of DM resistance so that the resistance will be more durable and resilient in the face of potential changes to the pathogen in the future. This includes using Seminole Pumpkin, San Jose Mountain Club Squash and Chinese Tropical Pumpkin as DM resistance sources.

South Anna Butternut, a variety Common Wealth Seed Growers developed from a cross between Seminole Pumpkin and Waltham Butternut, has shown promise for DM resistance in our small plot trials (see previous section). We have also gotten feedback from many farmers who have noticed its DM resistance and fruit quality. However, more information is needed to assess its potential in the region in comparison to other varieties in terms of not only DM resistance, but productivity and fruit quality.

CWSG has several new F2 seedstocks developed by crossing South Anna to other varieties (Atlas, JWS 6823, Chinese Tropical Pumpkin). We will begin selecting from these populations to develop new DMR varieties with traits such as shorter vine length, larger fruit size (for processing), smaller fruit size (for market), richer flavor, higher DM resistance, and higher fruit set. Part of the impetus for these crosses came from feedback from Clifton Seeds’ 2018 test of South Anna. They said it stood out for DM resistance but needed higher fruit set and larger fruit (many of their seed customers grow for processing).

In addition, Care of the Earth Farm has been trialing moschata squashes for several years. Their cross of Waltham and San Jose Mountain Club has shown promise (see below), but more work is needed for their goal of creating a new DMR butternut variety.

All our work with squash at Twin Oaks Seed Farm and Care of the Earth Farm is conducted on certified organic land, with minimal pest and disease control inputs. As a result our selections are well suited to survive the pest and disease challenges that Southeast organic growers face. This also stands to benefit conventional growers by reducing need for chemical inputs.

Very early planting is one way organic growers and some conventional growers have handled DM. Limitations are that summer-harvested butternut crops don't keep long into the fall, and that in some years severe DM comes early. South Anna, and other varieties we are developing, are intended to be grown in high DM conditions for fall harvest, allowing fruits to keep longer into the fall and winter. Note that assessing the performance of very early planted, summer-harvested butternuts is beyond the scope of this project.


Project Objectives:

The current project has three elements:

1)On-farm block trials: We will compare South Anna with two of the following popular butternut varieties (TBD): Quantum, Avalon, Atlas, Waltham. Trials will take place at five organic farms in Virginia, North Carolina, and South Carolina: Wild Hope Farm, Hickory Meadows Organics, Lomax Farm, Living Web Farm, and Twin Oaks Seed Farm. Each farm will grow two plots of South Anna and one plot of each of two other varieties (following what is known as an augmented trial design). Plantings at the different farms will also be looked at as replications when analyzing the data. The multi-row plots will be relatively large (4300 square feet) to more accurately represent normal production conditions. Trials will be planted somewhat late, approximately 140 days before expected first frost, to ensure presence of downy mildew. Data collected in the field will include downy mildew foliage ratings (along with documentation of any other diseases that may appear), and yield (measured by volume). Fruit quality will be evaluated with brix tests, dry matter tests, and keeping quality tests. A two-bushel representative sample from each plot will be collected at each trial site, and picked up for evaluation at Common Wealth Seed Growers in Virginia. Many of the growers involved attend the Carolina Farm Stewardship fall conference and we expect to be able to pick up much of the squash there.

2)Breeding trials at Twin Oaks Seed Farm and Care of the Earth Farm. Breeding trials at Twin Oaks Seed Farm will contain 200 separately-trained plants of several 2019 South Anna selections, and F2 plants from crosses between South Anna and Atlas, JWS 6823, and Chinese Tropical Pumpkin. Breeding trials at Care of the Earth Farm will contain 100 F3 plants derived from a cross between San Jose Mountain Club Squash and Waltham Butternut. We will measure DM resistance and yield for these plants, and approximately the best 30% will also be evaluated for fruit quality (brix, dry matter, shape, size, color, taste tests). Breeding trials will either be isolated to avoid crossing with other varieties, or plants will be self-pollinated.

3)The third element of the project is a screening of breeding lines and potential parents – to take place at both Care of the Earth Farm and Twin Oaks Seed Farm. Twelve 20-plant plots will be grown at each farm and assessed for DM resistance, yield, and fruit quality (brix, dry matter, shape, size, color, taste tests). At least half the screening entries will be grown at both farms. Entries could include: F1 crosses between South Anna and other varieties; different 2019 selections of South Anna; different selections from San Jose Mountain Club x Waltham; and varieties such as Quantam, Atlas, Avalon, Seminole Pumpkin, Tahitian Butternut, and Waltham.

Jared Zystro of Organic Seed Alliance will serve as an advisor to the project, providing help and advice in trials layout and in analyzing and presenting the data.


Click linked name(s) to expand/collapse or show everyone's info
  • Megan Allen - Producer (Researcher)
  • Pat Battle - Producer (Educator)
  • Shawn Jadrnicek - Producer
  • Gena Moore - Producer (Educator and Researcher)


Materials and methods:

This project included both variety trials and breeding trials. With the variety trials we were able to test and compare the butternut seedstocks we are working with to other varieties. In the breeding trials we compared different plants from our breeding populations and to obtain improved selections. 

At Twin Oaks Seed Farm:

The South Anna Butternut breeding trial included 90 separately trained plants. We evaluated for productivity, DM resistance, dry matter, brix, and keeping quality. We also did taste tests. Our selections in 2020 were especially focused on keeping quality. South Anna is a new butternut variety bred from an initial 2011 cross of Seminole Pumpkin and Waltham Butternut. Although we named the variety in 2017 and have been selling seeds since then, we are still doing active selection.

In a separate field we grew and evaluated about 100 plants of different crosses made with South Anna. This included South Anna crossed with a Guatemalan Ayote (F1 plants), South Anna crossed with Atlas (F2 plants), an F2 population that is 75% South Anna and 25% JWS 6823, and an F1 population that is 75% South Anna and 25% Chinese Tropical Pumpkin. We made promising selections from all these seedstocks, focusing on plants that have good eating quality, keeping quality productivity and DM resistance. The Guatemalan Ayote crosses were especially notable for their keeping quality and DM resistance. The JWS 6823 cross was notable for eating quality and small fruit size. The Chinese Tropical Pumpkin cross was notable for eating quality, appearance and productivity. The Atlas cross was very diverse but there were some good selections for eating quality, keeping quality and DM resistance. We also grew about 12 Guatemalan Ayote plants and selected for interior color (some are green), productivity, eating quality and keeping quality. Our goal was to self pollinate all the plants in this breeding trial, and we came close, with about 90 percent self pollinated.

In our large block variety trial we compared South Anna with three commercial hybrid butternuts - Atlas, Avalon and Quantum. Each variety was planted in a 40x80 foot block. Avalon showed poor downy mildew resistance, with the plants dying completely by mid September. Atlas and Quantum showed DM resistance and productivity comparable to South Anna. Quantum also had better keeping quality. Atlas had problems with fruit splitting due to heavy rain. South Anna had much better eating quality than Quantum and Atlas.

In our small block variety trial we compared 12 seedstocks including several different South Anna crosses. Blocks were 20x30.

At Care of the Earth Farm:

Megan Allen of Care of the Earth Farm conducted a breeding trial with populations derived from a cross between Waltham Butternut and San Jose Mountain Club (a necked tropical pumpkin from Costa Rica), and was able to obtain improved selections. Megan also conducted a small block variety trial.

Large block trials also took place at Wild Hope Farm (South Carolina), Lomax Farm (North Carolina), and Living Web Farms (North Carolina).

Research results and discussion:

See some discussion of results above - I will add to this section later, with more discussion as well as data spreadsheets.

Participation Summary
8 Farmers participating in research

Educational & Outreach Activities

1 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

300 Farmers
4 Ag professionals participated
Education/outreach description:

We hosted a field day on September 21st, 2020 at Twin Oaks Seed Farm in Louisa, Virginia. About 35 farmers, apprentices and farm workers from Broadfork Farm, Shalom Farms and Acorn Community Farm attended. We looked at and talked about the South Anna Butternut breeding trial, large and small block trials, and the diverse squash breeding trial - all located in separate isolated fields at the farm.

On January 28th, 2021, Edmund Frost was part of an online presentation about tropical squash organized by the Culinary Breeding Network as part of their online Winter Squash Week. Co-presenters included Linda Wessel-Beaver of University of Puerto Rico, Glenn Teves of University of Hawaii Extension, and Jay Bost of University of Hawaii. Here's a link:

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

Project outcomes:

The primary impacts of this project are the improvement and development of new butternut squash varieties adapted to the Southeast and mid-Atlantic regions. This is a long and slow process, but we feel that we made good progress with selections in 2020.

Another goal was to compare South Anna to leading commercial varieties used in the region. The information gathered in this comparison will be helpful to farmers as they choose which varieties to grow. It has been helpful to us in identifying that improving keeping quality in South Anna and derivatives is a need, and that we are doing well on eating quality compared to commercial hybrids.

More information to come.

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.