Seed Increase Trials Lead to Release of Promising New Disease- Resistant Varieties


Investigator: Michael Mazourek, Department of Plant Breeding and Genetics, Cornell University, Ithaca, New York.
Project location: Cornell University’s 30 acre certified organic Freeville Organic Research Farm, located 10 miles north of Cornell’s Ithaca, New York main campus.

Cornell University has for several years been actively involved in the improvement of vegetable varieties for organic systems. Many of these varieties are now commercially available to organic growers. In this project, Cornell plant breeder Michael Mazourek coordinated seed increases of several new organic squash, melon and cucumber varieties, aided by a pollination cage system to house the growing plants which assist in disease and insect pest management during seed development. Several cucumber varieties undergoing development in this study are now available through organic seed suppliers.

Project links: Investigator Michael Mazourek’s complete project report, seed trialing and increase handout, and a pictorial guide to pollination cage assembly

Project summary: Organic seed is a critical part of organic vegetable production. For certified organic growers, the use of organic seed is required when it is available. Also, using organic seed supports organic practices at a crucial step in the organic supply chain.

The objectives of this project were:

  • To generate seed of improved organically bred vegetable lines;
  • To allow growers to evaluate multiple versions of each variety;
  • To provide feedback as to which cultivars best suit their needs, and;
  • To use that information to encourage the production, availability and distribution of these varieties through organic seed companies.

Based on the needs voiced by organic vegetable producers, breeding programs were initiated several years ago in cucumbers, melons, bell peppers and winter and summer squash varieties. The common theme of these projects was the use of grower-identified varieties and addressing growers’ requests to improve earliness and disease resistance while maintaining their valued flavor.

Diseases and insects affecting these crops include cucumber mosaic virus, transmitted by aphids to peppers and cucurbits, and watermelon mosaic virus, which affects cucurbits. In the northeast, cucumber beetles can devastate foliage and transmit bacterial wilt and squash mosaic virus, which can contaminate the produced seed.

Excluding insect pests and pollinators that could bring in undesirable pollen was considered desirable, as well as deterring species outcrossing. Pollination cages were selected as a solution favored by USDA germplasm curator collaborators who mentored us in the adoption of these structures. Pollination cages to house the growing plants were erected to benefit the health of the plants and seed yield and quality by excluding most insects and the diseases they vector.

Initial seed increases for evaluation and distribution to farmers for testing included:
Melon varieties:

  1. ‘Golden Gopher’-derived powdery mildew resistant (PMR) melon
  2. ‘Farmer’s Daughter’ PMR melon similar to ‘Collective Farmwoman’
  3.  Medium-sized PMR Honeydew

Cucumber varieties:

  1. ‘Silver Slicer’, long white PMR cucumber
  2. ’Salt and Pepper’, small white PMR cucumber
  3. Long White PMR cucumber selection

Summer and winter squash varieties:

  1. Orange striped summer squash
  2. Improved Costata Romanesco type squash
  3. Large PMR Butternut selections
  4. ‘Oro Verde’ green striped PMR butternut
  5. ‘Bright Eyes’ small butternut with “eye spots”

One exception from the original project plan was that generation of seed for bell pepper varieties was halted after it was determined that pepper plants became infected with a virus prior to transplanting into the cages.

The panel of vegetable lines was grown in a greenhouse and seedlings were hardened off prior to transplanting. A field was amended with compost, and three raised beds with plastic mulch and drip tape were formed to run the length of each pollination cage. A metal frame twelve feet wide, six feet tall and forty-eight feet long was constructed over the beds. Mesh fabric for the cages was sewn to fit the supports with an additional flap around the bottom edge to be sealed and secured by soil and a zippered entrance on either end. Transplants were planted inside the mesh cages and fertilized with fish emulsion and irrigated as needed. (Further planting details and densities and other methodologies are available in the complete project report, in the seed trialing and increase handout, and a pictorial guide to pollination cage assembly.)
image of hive in pollination cave

Hives of honeybees were introduced into the pollination cages at flowering to pollinate the crops. While bumblebees are commercially available, they are not as effective as honeybees in our experience. A bumblebee hive tends to contain far fewer individuals and is sensitive to handling during shipping and placement of the hives. Honeybees immediately flow from the hive by the hundreds when the hive is opened and swarms of bees are active in the flowers the same day. Honeybee hives can often be borrowed or rented from a local apiary. Rather than a large hive, a small nuc such as the one pictured (see photo) is more than sufficient. After about a month, the hive should be swapped out of the cage because there are not enough flowers in the cage to sustain the bees. Rotating the hive to a field of alfalfa provides ample food for the bees and does not risk contaminating the crop with vegetable pollen.

Fruit was harvested at maturity. Fruit that had any symptoms of disease or had started to rot were discarded to avoid contaminating seed lots. Seed extraction has become a popular student activity; rather than hiring staff to spend hours performing this monotonous task, classes that visit us in the fall on field trips joyfully scoop seeds from the pickup-truck loads of cucumbers and smash open squash with cinderblocks. We take care that each lab group works with a single cultivar to avoid cross-contamination.

Seeds were allowed to ferment, rinsed, and dried in a forced-air oven. Dry seed was cleaned using an air column. Germination of all seed lots was tested and seeds were packaged for transfer to storage at a Cornell University facility that maintains low temperature and humidity year round.


Related link: New Varieties for Northern Growers: Organic Vegetable Options Expanding, from Farming Magazine, by Tina Wright.

Organic Agriculture at Cornell University sponsors a Freeville Organic Research Farm Field Day every August. Contact Michael Glos at for details.