The Art and Science of Rose Hybridization

If you’ve ever walked through a rose garden or spent time browsing rose varieties online, you know there’s a considerable variation in rose plants. There are climbing roses with large, open, yellow blooms, miniature shrub roses with tightly swirled red flowers, and everything in between. While some of this variation naturally exists, rose hybridization has led to many new cultivars. In this guide, I’ll explain some of the basics of rose breeding and dive into the art and science of rose hybridization so you can understand how your favorite roses came to be.

The Art and Science of Rose Hybridization

Understanding the Basics of Rose Genetics

Roses, like all plants, keep their genetic material in their genes. These genes combine to form DNA, which is contained in chromosomes. All of the chromosomes combine to form the genome. In short, the genome describes the total genetic makeup of an organism, and a gene is a tiny part of the genome. 

By altering a rose plant’s genes, you can impact characteristics like the rose flower colors, disease resistance, and fragrance. Since individual plants in the same species have similar genes, they exhibit similar characteristics. For example, all Virginia rose plants (Rosa virginiana) grow four to six feet tall, produce single-bloom pink flowers, and form large rose hips.

When you cross two species of roses together, like crossing one Virginia rose with another Virginia rose can cause some genetic variation, the offspring will largely resemble the parent plants. However, crossing a Virginia rose with another rose species—let’s say a China rose (Rosa chinensis)—leads to offspring with genomes that are mixtures of the two parent plants. The plants in this first generation of hybrids are known as F1 hybrids, and they won’t necessarily resemble each other.

If you cross two F1 hybrids together, you’ll end up with a F2 hybrid.

The History of Rose Hybridization

Hybrid roses growing in a field

Humans cultivated roses long before hybridization took off. Records show that gardeners tended to roses as early as 3000 BC. Many of these roses were individual species.

Eventually, humans began crossing individual rose species to form hybrids. However, things really took a turn when people introduced the China rose (Rosa chinensis) to Europe in the 1700s. This introduction allowed for the development of the first hybrid tea rose in 1867, a moment many consider the start of modern roses.

When botanists talk about roses, they break the plants into three main categories: wild (or species), old garden, and modern garden. Wild roses have not been hybridized, old garden roses were hybridized before 1867, and modern garden roses emerged after 1867.

The Process of Hybridizing Roses

A cluster of large pink David Austin roses in bloom

Hybridizing roses involves taking the pollen from one species or cultivar of rose and using it to fertilize the stigma of another type of rose. Botanists refer to the pollen giver as the father plant and the receiver as the mother plant. Once the mother plant is pollinated, it will produce seeds that contain genetic material from both plants.

This F1 hybrid not only contains a mix of the parent plant’s genes, but it also exhibits hybrid vigor. This means that the mixing of genetic material leads to improved growth, health, yield, or other favorable traits.

Plant breeders can later cross F1 hybrids with other roses to produce new hybrids. The offspring of two F1 hybrids are known as F2 hybrids.

Challenges and Breakthroughs in Rose Hybridization

Some of the main challenges in rose hybridization include varying numbers of chromosomes in rose plants, unpredictability in inherited traits, and infertile plants. Some roses have 14 chromosomes, but other plants have up to 56. Many commercially-bred roses have 21 chromosomes. These differences make it difficult to target specific genes and characteristics to carry them to a new generation of plants.

Additionally, roses take multiple years to grow from seeds into seed-producing plants. That means that breeding is a long process. And since plant breeders want to select for characteristics including flower color, fragrance, disease resistance, and height, it’s difficult to produce a plant with all of the desirable traits.

Some breakthroughs in rose hybridization include the limited mapping of some rose genomes. Since roses have different numbers of chromosomes, plant breeders must look at roses in a few groups. Although they need to complete further genetic mapping, scientists have determined which genes account for important characteristics like flowering time and black spot resistance in roses with 14 chromosomes.

Breeders are also working to create roses with large amounts of essential oils.

The Role of Technology in Modern Rose Breeding

The Role of Technology in Modern Rose Breeding

One major technological advancement in rose breeding is the development of marker assisted selection. This process involves determining which genes are responsible for certain characteristics and which DNA sequence (allele) creates a desired trait. Breeders can then select plants with the desired allele and end up with the favorable trait.

For example, let’s say a plant breeder has a plant they love, but they want to end up with a similarly-looking plant that’s resistant to black spot. One option is to cross-breed this plant with a resistant variety, let the new generation grow out, and select resistant plants. However, another option is to breed the plants and use marker assisted selection to determine which seeds contain the allele for black rot resistance. Using marker assisted selection speeds up the process.

Artistry in Rose Hybridization

Since gardeners grow roses for their beautiful flowers, many rose breeders focus on breeding plants with desirable flower shapes, colors, and fragrances. Breeders have created roses with six-inch flowers, multi-color blooms, and highly fragrant flowers. 

Hybridization has also had a big impact on flower shape. While most species roses have single or double layers of simple petals, you can find modern roses with multiple layers of ruffled petals and tightly bound swirls.

Rose hybridization has created some of the most famous rose varieties, including Knock Out® series, Easy Elegance® series, damask roses, hybrid tea roses, floribunda roses, and Grandiflora roses. It has also led to the creation of the famous David Austin roses and can also help with eco-friendly rose gardening practices.

Ethical and Environmental Considerations

A single vibrant red rose flower in bloom against deep green foliage

Since rose sales account for millions of dollars annually, it’s no surprise that rose breeding is a hot business. As is the case with many ornamental and edible plants, few major private companies complete the majority of rose breeding. These companies are wary of sharing the genetic information they’ve worked on, making it difficult for the public and other companies to learn from their advances.

As far as the development of new roses goes, most roses are hybridized through physical cross-breeding. However, the first blue rose was bred through genetic modification. This rose contains genetic material from a bacteria, which allowed the petals to express a blue color.

In the future, rose breeders will continue to map more of the rose plant genome for plants with varying numbers of chromosomes. This will allow them to learn which genes are responsible for which characteristics and create plants with desired traits.

Many breeders are focusing on how these plants can withstand a changing climate. That means breeding plants for drought tolerance, cold hardiness, and the ability to withstand heavy rains. Breeders will also continue to select rose plants resistant to diseases such as black spot and powdery mildew.

Wrapping Up

Now that you know the impact that hybridization has had on rose varieties, you can browse through your favorite cultivars with a bit more understanding. Remember that plant breeders continue to produce new varieties, so you can expect to see more types of roses hitting the market in the future.

Contributing Editor | briana@petalrepublic.com | Full Bio

Briana holds a B.S. in Plant Sciences from Penn State University. She manages a small market garden where she grows vegetables and herbs. She also enjoys growing flowers and houseplants at home.

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