Plant Breeding Methods – How to Cross Two Plants

If you frequently go to specialty food stores like Trader Joe’s or Whole Foods, you’ve seen “new” fruits being added to the shelves. For example, the “pluot” or the cotton candy flavored grapes. Another that you may not know is a relatively new fruit is the kiwi, which derives from a very unappetizing, small berry plant in China.

These, and many other more typical fruits like common strawberries and almost all citrus varieties, are the result of plant breeding methods. They’ve been known to be called “designer fruits,” and combine the characteristics of two plants within the same species. Designer fruits are generally produced by using two different plant “parents” and cross-breeding to produce a hybrid offspring.

What Is Plant Breeding?

Plant breeding may sound like a process that takes place in a laboratory by very serious men wearing white coats. While that can certainly be true in a commercial setting, it is not at all the only way that plant breeding happens.

In short, plant breeding is the intentional manipulation of a plant species to produce offspring with desirable characteristics. If this sounds scary, it’s really not. The process happens completely naturally, and is how some plant species have different varieties that each grow well in different environmental conditions.

One pepper plant native to the desert may be more tolerant to low moisture, while another pepper plant can handle occasional flooding or downpours. This is possible due to countless years of adaptation through natural plant breeding.

The part that makes plant breeding unique is that people can carefully determine which two plants should be crossed. Similarly, in a farm setting, a farmer will often choose which crops should be planted in the following year, based on which individual plants were healthiest.

Plant breeding is one of the oldest accomplishments of man.

(Source)

Plant breeding has helped farmers develop stronger and more resilient crops. It has helped produce crops that grow faster or grow in a wider variety of temperatures and climates. And perhaps most importantly to the food industry, it has developed more disease resistant plants.

What Kinds Of Plants Can Be Crossbred?

Any two plants of the same genus can usually be cross bred. When breeding plants, growers typically cross two species that are within the same genus. For example, the very famous Ghost Pepper was born of a cross between Capsicum chinense and Capsicum frutescens, two pepper species that are within the same genus, Capsicum.

The possibilities are effectively endless. Just take the Orchidaceae family of plants (Orchids). There are over 28,000 accepted varieties of Orchid species. The variety is truly staggering for just one family of plants. So, if you happen to be an adventurous gardener, you may have an interest in crossing two of your favorite vegetables or fruits.

Plant Breeding vs Genetic Modification

You may be wondering whether plant breeding is the same as genetic modification. Well, put simply, no. Plant breeding is the natural selection of ideal plants and crops, while genetic modification involved biological modification at the cellular level.

Genetically modified organisms, or GMOs, are always born in a laboratory. That is why they stir up so much controversy, including the argument that you shouldn’t be able to put a patent on life (source).

Is Plant Breeding Safe?

Standard plant cross-breeding is a natural process which occurs when pollen transfers from one plant to another. It is a key form of reproduction in many plants and is generally believed to be a safe process.

In mass production crop breeding, precautions are taken to ensure foods are safe to consume. Most plants in the world produce at least some level of harmful ingredients, but in very small amounts. Through breeding it is possible that a new variety will contain higher levels of these substances (source).

There are less natural forms of plant breeding, like mutation breeding, where different forms of light radiation or chemicals are put onto seeds to modify the resulting plants. These methods can be more unpredictable and should be thoroughly researched before attempting. Here is the wikipedia article on mutation breeding.

Plant Breeding Methods

Mass Selection

Mass selection is the more basic of the plant breeding methods. Mass selection breeding involves visual selection of individual crops or fruits that appear to be superior. Then, the seeds from these plants are used to plant the next line of crop, usually resulting in a more consistent plant.

This method is simple, but effective, especially in large-scale operations like growing rice or other self pollinated crops.

Another similar method that falls into the mass selection category is to simply remove crops or plants that look undesirable. In effect, the result is equivalent and may be more unbiased.

Hybridization

Hybridization is a more advanced form of the methods of plant breeding, and is widely used in both self and cross-pollinating varieties of plants. It involves crossing two genotypes, each of which lack a desirable characteristic which is held by the other. The goal is to create a “hybrid” offspring plant which will be superior to both of the “parent” plants.

The method used to achieve this is by carefully selecting two parent plants and cross pollinating them. This process causes the seeds to grow into a hybrid variety, imbued with some of the characteristics of both parent plants.

For a great example of someone crossing pepper plants, watch this video by Khang Starr on YouTube:

Mutation Breeding

Mutation breeding is the process of exposing seeds to specific chemicals or forms of light radiation, like x-rays or gamma rays, to change the characteristics of a plant. There is some controversy over mutation breeding, and whether the process is natural or not.

What Is Cross Pollination?

Cross pollination is when pollen from one plant’s flower is mixed with the pistil of another plant’s flower. Typically, this occurs in nature when pollen is carried by wind and insects, like bees, from one plant to another. The pollen is what initiates the production of seeds on the plant, which will later grow into a new generation of the species.

First generation hybrids will typically have characteristics from both of the parent plants. However, further generations will tend to be less consistent with their new characteristics. It can take 5 or more generations of careful hybridization breeding to stabilize a new species. This is why, if you take the seeds from a 1st generation hybrid fruit (maybe a tomato variety that you like from the store) and grow it at home, you may not end up with the fruits you were expecting.

Bumble Bee Pollinating
Bee Pollinating Flowers

How to cross pollinate two plants

Let’s call the first plant the “giver” and the second plant the “taker.” The giver is the plant that will offer up some of its pollen to the taker. The taker will have the giver’s pollen placed on one of its flower’s pistil. Here is how to cross two plants:

  1. Always use sterile materials.
  2. Locate an open flower on the giver plant. This flower must be producing pollen.
  3. Use a sterile container to catch some of the pollen from the open flower. Pollen is very small, dust-like material that falls from flowers. You won’t need too much!
  4. Locate a closed flower on the taker plant. Ideally this flower is just ready to open its flower.
  5. Use small snippers (tweezers or small scissors work) to cut away the flower petals, and carefully cut away the stamen, leaving just the pistil in the center.
  6. Use a clean cotton swap to place the giver’s pollen onto the taker’s pistil.
  7. Use a small, labeled plastic bag to quickly cover the pollinated flower to prevent self pollination on the taker plant. Labeling is important to keep track of which fruits were pollinated by which plants.
  8. Reverse the process, so that the taker and giver reverse roles.
  9. When the flower starts producing a fruit body, you can remove the plastic bag.
  10. When the fruit is fully produced, use the seeds to grow your hybrid plant!

The new features on a 1st generation hybrid is something called hybrid vigour, or heterosis, and it is ultimately the goal of plant breeding.

It is smart to pollinate more than one flower on the taker plant. This will increase your chances of having a successful hybridization. Cross pollinating is a slow process, but the fruits of your labor can be well worth the time!

One of the most important factors when plant breeding at home is to be very careful when cross-pollinating. Transferring pollen from one plant’s flower to another’s can be tricky. You want to ensure that the receiving plant’s pistil has not come in contact with any other pollen. If it has, your efforts may have been in vain. So, we take some precautions when cross-pollinating.

Hybrid Vigour in Plant Breeding

Hybrid Vigour, or Heterosis, are the improved characteristics of a hybrid plant variety when compared to its two parental plants. In other words, the increased size, faster growth rate, sweeter or spicier flavor, etc. over the original two plants.

Plant breeding allows growers to choose which characteristics to focus on. That is why plant breeding is so valuable, (and cool for home growers to experiment with).

Some really interesting varieties have come from plant breeding methods. For example, cotton candy grapes have been very popular in recent years. They’re the result of two species of grape being crossed to produce a unique, very sweet flavor:

Cotton Candy Grapes

Another example of heterosis in plant breeding is the increased size of apples and other fruits. There are other possible reasons for larger fruits, but in effect, plant breeding can deliver the desired result.

Plant Breeding Methods For Higher Yields

If you are trying to breed plants with the end goal of higher yields, it is ideal to start with a variety of the plant that produces prolifically, and cross it with the plant that underproduces. In this situation, you probably have a plant that has great tasting fruit, but doesn’t produce enough of them! This is a classic predicament in plant breeding, and can take several generations to begin seeing desirable results.

Unfortunately, for higher yields, it is ideal to have a larger scale operation to speed up the process. If you have more places to grow individual plants, you can more quickly experiment with resulting hybrids. More plants can also lead to increased likelihood of unintentional cross pollination, so be careful!


We hope you enjoyed this article, and are excited to get started with one of these plant breeding methods. Crossing two plants can make gardening much more exciting, with amazing results to share with friends and family.

Have you had success with plant breeding at home? Share with us in the comments! We love seeing new varieties of plants (and especially peppers!).

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