Summer and Winter Squash Research and Breeding for the Southeast

View the project report

Commodities

• Vegetables: cucurbits

Practices

• Crop Production: crop improvement and selection, plant breeding and genetics

Research, breeding, selection and seed production work with squash in the Southeast has the potential to improve the pest resistance, disease resistance, quality and productivity of varieties available to Southeast growers.

In this project we will research several kinds of summer and winter squash, with goals of identifying existing varieties that are better suited to Southeast conditions, and of creating new ones. We are seeking varieties that thrive, produce, and keep well in our hot, humid weather and can withstand the pest and disease pressures we experience here. They should also have good eating quality and be easy to manage and harvest. 

With summer squash our research will take the form of variety trials in 2023, and then follow-up breeding and variety trials in 2024. In 2024 we will also do seed production of trial standouts in pollination cages. We will be trialing both Cucurbita pepo and Cucurbita moschata varieties.

With winter squash, where we already have done many years of research and breeding work, we will focus on testing the feasibility of using pollination cages with introduced bumble bee pollinators for C. moschata squash seed production, as well as on continuing selection and comparison of existing breeding lines. We have already developed and released downy mildew resistant varieties South Anna Butternut and Xiye Butternut, and have identified, improved and released several additional varieties. With access to more isolation plots we are on track to release additional varieties, with better keeping quality and other useful traits (see below), in the next 1-2 years.

Using screen cages could also be an important element of maintaining the USDA moschata collection. Our project aims to model their effective use for moschatas in our region, and will give us needed experience to work on (and help others work on) regenerating the USDA moschata collection in the future.

We are in contact with growers who have used pollination cages for seed crop isolation in other regions, including Louisa Brouwer of Ferry Boat Seeds in Washington, Jay Bost (who used screen cages in Hawaii and has recently moved to North Carolina), and Micaela Colley of Organic Seed Alliance in Washington. We will also be referring to a project on screen cages from Hawaii: “DIY Screen Cages for Insect Management in the Tropics.”

We are not however aware of growers who have used screen cages for cucurbit crops in the Southeast, or for moschata seed production. So while we have several models to draw from in making screen cage growouts successful, we also expect to demonstrate and trouble-shoot something new for our region.

The new winter squash populations at Twin Oaks were developed mainly in breeding trials that were part of our 2020-2021 SSARE producer grant “Breeding and Evaluation of Butternut Squash Varieties for Southeast Organic Farms.” We also followed up on that research in 2023 with unfunded breeding trials.

More about the populations we’re working with at Twin Oaks:

-75% South Anna Butternut, 25% Chinese Tropical Pumpkin (F4). A butternut with good keeping quality, productivity, eating quality and sweetness. The flesh has finer texture than South Anna, and larger seeds. In 2022 we grew 20 F3 plants and obtained self-pollinated seed from several promising selections that we intend to recombine, in large-fruited and a small-fruited groupings, each in its own isolation cage. The advantages of this population over South Anna are better keeping quality, potentially better yields, and more uniform fruit sizes.

-‘Butternut 200’ (75% South Anna and 25% JWS 6823) (F5). This comes from a 2020 breeding trial selection. It is a small butternut with excellent nutty flavor and fine texture we think could be competitive with ‘Honeynut’ as a high quality niche variety, but has the added advantage of good downy mildew resistance. The small size is desirable for market and CSA growers. In 2022 we observed variation in productivity between plants, but obtained hand crosses between more productive plants. Productivity and keeping quality may not be optimal for this seedstock, but we believe there is room for fine tuning. For isolation cage in 2023.

-South Anna x Guatemalan Green Ayote F4; and South Anna (62.5%) x Guatemalan Green Ayote (25%) x JWS 6823 (12.5%) F3. These populations come from selections made in our 2020 breeding trial that we crossed together. Fruits have excellent keeping quality, good productivity, fine to medium texture, small seeds, and good flavor, dry matter and sweetness. Exterior coloration is diverse - some retaining green or green-orange stripes when ripe, while others have standard butternut color. Stands out for keeping quality. We will likely hand pollinate these to isolate different colors.

-Chinese Tropical Pumpkin. A variety derived from Crowning F1, with excellent flavor and productivity. Mostly flat ribbed pumpkins, but there are necked offtypes we want out of the population. We made progress in 2022 by crossing three good plants to each other. But we want a broader genetic base, so we’ll self pollinate more good plants in 2022.

-Moranga Coroa x Winter Sweet F4. A cucurbita maxima variety we are breeding for vine borer resistance and rich kabocha-type flavor. Excellent keeping quality, and some with excellent flavor, but needs to be stabilized for flavor. For self pollination in 2024

At Care of the Earth Community Farm we are working with populations derived from a cross between Waltham butternut and a Costa Rican variety called San Jose Mountain Club. The original goal was a good tasting butternut with resistance to downy mildew, black rot, and bacterial wilt – which were all serious problems for butternut crops at the farm. We have released Xiye as a variety, though it is still in need of refinement. It has good disease resistance, eating quality and productivity, and has proved a valuable part of Care of the Earth’s CSA production. It is more determinate than South Anna. Fruit size and shape needs stabilization. We also have another selection from this population - with small fruit and shorter vines. It needs further evaluation and stabilization. Our 2020-2021 SSARE grant also contributed to this population’s development.

Summer Squash

We are proposing two summer squash research efforts, one with C. pepo squash at Care of the Earth Community Farm (where vine borer pressure is not present), and the other with C. moschata squash, at both Twin Oaks Seed Farm (where vine borer is present) and Care of the Earth Community Farm.

We are aware of nine varieties of C. moschata summer squash: three from Korea, two from Brazil, three derived from the Italian variety ‘Tromboncino,’ and one from Veracruz, Mexico. The Korean squashes are listed as hybrids, and one is only available with treated seed, which we can’t use on our organic farms. Altogether in 2023 we will screen eight C. moschata summer squash seedstocks at Twin Oaks Seed Farm in year one, in two successions so that we can better understand the difference between early and late season needs. One variety will be replicated three times in each succession to confirm field uniformity. One succession of these same moschata varieties will also be grown and evaluated at Care of the Earth Community Farm. Each plot will have five plants, with a total of 180 row feet per succession. We don’t know how vigorous the vines are with many of these so will give them extra space.

In the 2023 C. pepo summer squash trial at Care of the Earth Community Farm we will screen 13 varieties (including 4 varieties from Mexico, 6 open-pollinated varieties currently cultivated in the Southeast, and 3 hybrid controls - Elite, Gentry, and Respect - that were standouts in trials at LSU and UGA). Gentry will be replicated three times to confirm field uniformity. This will be planted in two successions so that we can better understand the difference between early and late season needs. Each plot will have five plants, with a total of 200 row feet for each succession.

In the summer squash trials we will measure yields; rate the impacts of diseases including downy mildew, bacterial wilt, and yellow vine disease; rate damage caused by vine borers and other insect pests; and assess eating quality, fruit shape, plant architecture and determinacy. In the second succession of both the pepo and moschata trials, we will be doing some hand-pollinated crosses between varieties that stood out in the first succession, as well as saving hand-pollinated F2 seed from any standout F1 hybrid varieties – this will set ourselves up for selection work the following year.

In the 2024 summer squash trials we will dedicate 300 row feet to follow-up summer squash breeding and variety trials. This will include advancement and evaluation of F1 crosses made in 2023; evaluation and selection from F2 populations derived from crosses made in 2023 and increased early in the year in 2024 in a greenhouse; and evaluation and selection from F2 populations derived from commercial F1 hybrids; as well as any comparison of varieties that may be needed to confirm or expand 2023 findings.

Winter squash

At both Care of the Earth Farm and Twin Oaks Seed Farm we have been working on developing new winter squash varieties (mostly butternut) for several years.

In 2023 at Twin Oaks Seed Farm we will grow three promising new winter squash populations in screen isolation cages. The purpose of this is to test the suitability of screen cages with introduced pollinators for producing moschata squash seed in our region; to save selected seed from each of the populations; and to evaluate the populations, comparing them to each other. Plants within each plot will be allowed to intertwine, but then fruits will be traced back to the plants they come from, and each plant (and each plot as a whole) will be evaluated for yield, keeping quality, eating quality, and appearance. Disease and pest pressure will also be evaluated (screen cages will not be put in place until just before flowering so there will be a chance to assess insect pest pressure). This method will allow for ongoing maternal selection of the seedstocks. We will also evaluate seed quality and measure seed yield. Each 50x14 screen cage will have 15 plants spaced at 2.5 feet. We are expecting that some of these will become named varieties, ready to sell at the end of 2023 or 2024. In addition, outside the isolation cages, we will grow, evaluate, self-pollinate, and make new selections from 60 separately trained winter squash plants from other populations. See previous section for descriptions of populations.

Screen cage design will likely involve using caterpillar tunnel-style hoops spaced at 10 feet and covered with insect exclusion netting. We have priced structures at approximately $1200 each. Hives of Bombus impatiens bumble bees will be used for pollination. Each hive costs approximately $200.

In 2023 at Care of the Earth Community Farm we will grow and do maternal selection from 100 separately-trained plants of the population derived from a cross between Waltham butternut and San Jose Mountain Club squash. We will plant 5 plants each of 10 hand-pollinated selections from 2022 of the already named and released Xiye butternut. It continues to need refining. We will do observation and selection for resistance to bacterial wilt, DM and black rot as well as productivity, vine length, fruit size and shape, flavor, and keeping quality. We will also plant 5 plants each of 10 selections from a gene pool with smaller fruit and compact vines.

In 2024 we will use the three screen cages for 3-5 squash seed production crops (we may be able to fit one pepo and one moschata in some cages if varieties we decide to produce are compact). Compared to the 2023 growouts these will involve less intensive evaluation of fruit quality but will still allow us to continue to confirm feasibility of squash seed production in screen cages, correcting any problems that may have come up in 2023. At least one of the cages will be used for summer squash seed production, and at least one will be used at Care of the Earth Community Farm.