The Story of a Seed: Hybrid Onion Edition
How does an onion seed get from plant to packet? Read on to learn about the intricacies of hybrid onion seed development and production through looking at the variety Red Carpet F1. We hope the story of a seed entices you to try a new onion variety this season!
An onion flower emerging.
Onions are day length sensitive and must be selected for the appropriate growing location’s latitude to produce and yield healthy bulbs. They can be affected by a range of pests and diseases in both the field and storage, many of which will adversely affect the yield and quality of the crop, so ensuring pest and disease tolerance or resistance is important as well.
Red Carpet F1 was developed by the breeders at Bejo Seeds with the goal of offering an improved red storage onion with excellent disease and pest resistance. Some of the specific traits Bejo’s onion breeding team are looking for when they develop a new variety like Red Carpet F1 include resistances to Fusarium, Downy Mildew, Pink Root and Thrips; bulb quality and length of storage; desirable size, shape and color; and ideal day length, earliness and harvest timing.
A flowering onion seed head as it dries.
Let’s start with the maintenance of the maternal and paternal parent lines. There is a very specific breeding technique that has been developed for hybrid onions in order to perpetuate reproduction of the parent lines. The crux of this technique is starting with a male-sterile female parent line.
In an ordinary onion cultivar, male and female parts are in the same flower. This is called the perfect flower, and makes it possible for each plant to pollinate itself. (Onions are pollinated by insect pollination via honeybees, wild bees and flies.) To force cross-pollination and produce hybrid seed, it is therefore necessary to remove the pollen of the female parent plant – in plant breeding, this is commonly done by hand and is called emasculation. This process is extremely labor-intensive and is a very delicate process. Due to a genetic mutation that was discovered in the 1920s, there are now onion plants available whose flowers are not perfect, i.e., they contain no fertile pollen. In other words, their flowers have only female parts, and emasculation is unnecessary because the plant cannot pollinate itself. It can, however, be easily cross-pollinated by another onion variety (one whose flowers are perfect) without the need for hand pollination.
These sterile lines are critical for hybrid production because they speed up the cross-pollination process, with no manual emasculation necessary. Male sterility must occur on the female parent side, since it is from the female parent plants that the first generation (F1) hybrid seed will be harvested. For ease of reference moving forward, let’s call this parent line A.
The sterility in a female parent line comes from the genetics of one particular onion variety, 13-53, discovered and propagated at the University of California Davis in the 1920s. When 13-53 is crossed with any other perfect flower onion cultivar (i.e., a self-pollinating variety), the offspring will be one of three kinds: all plants will have perfect flowers, or some plants will have perfect flowers and some plants will have female flowers, or all the plants will have female flowers.
Since the goal is to produce as much seed of line A as possible, the crosses that produce all female flowers are those that breeders choose to work with. In order to perpetuate seed production of line A from which to harvest the finished hybrid seed, it is necessary to be able to reproduce the seed of line A using cross-pollination with 13-53. This reproduction has been found to be possible by backcrossing the sterile female cultivar 13-53 to a perfect flower cultivar that is identical to line A, but sterile. This is a maintainer line we’ll call line B. With each backcrossing to line B, the female offspring look more and more like line B, and after four or five generations there is no difference in appearance. These female offspring, when backcrossed to line B, continue to produce seed that grow into all-female plants – these seeds are line A.
Freshly harvested Red Carpet F1 onions.
The hybrid male parent line (let’s call him line C for short), is easier to reproduce for seed. Line C is self-pollinating, so the plants can be grown and harvested for seed without forced cross-pollination.
Finally, let’s talk about how to get the finished hybrid seed – F1, for short. In order to produce F1 seed, the sterile female parent, line A, is inter-planted with the hybrid male parent, line C. Because line A is sterile, there is no risk of self-pollination. If proper isolations are maintained, there is no risk of cross-pollination either, except with the pollen present on line C, which is desirable. The resulting seed from these crosses will be harvested from the plants of line A, and will be viable F1 seed.
Onions are biennial plants, which means they take two years to complete their biological lifecycle, from seed to seed. This means that the hybrid onion seed that we package for sale in 2019 was harvested in 2018 from parent lines that were planted in 2016.
The Market
The first step to development of a new onion variety is to understand what a desirable onion looks, tastes, and grows like. Farmers are always in need of varieties that are better: better tasting, faster growing, more disease resistant, etc. Each of these elements is very important to the grower, who depends on a variety’s characteristics to perform well in their unique growing conditions and fulfill their unique market needs. These needs are researched by plant breeders and geneticists to guide them in developing varieties that can fit the requirements of the grower.An onion flower emerging.The Breeder
Once a market need is identified, the breeders at Bejo get to work with their plant germplasms to attempt to develop a variety that fits the special niche their growers are looking for. In the case of a hybrid onion like Red Carpet F1, the whole process of breeding a new variety and making the seed available to growers takes 10 to 15 years. At Bejo, breeders start by crossing maternal and paternal lines (more on this later). The resulting seeds are then grown into full plants and undergo extensive trials at test stations around the world to experience diverse climate conditions. Part of the trialing process is making selections from the resulting genetic lines for the traits the breeders are looking for. Bejo selects breeding lines to fit local market needs, including making sure the plants are suited to local circumstances like day length, climate, fertilization, pest control, and irrigation – all very important focuses for an organic grower.The Seed Grower
Once a hybrid breeding line is considered “finished,” i.e. it encompasses all the traits the breeders are looking for, Bejo’s next responsibility is two-fold. First, they must maintain both the maternal and paternal parent lines of the hybrid variety. Second, they must use the parent lines to produce hybrid seed.A flowering onion seed head as it dries.Freshly harvested Red Carpet F1 onions.