News
RNA-Based Approach Shows Promise for Managing Powdery Mildew in Roses
June 18, 2026
Powdery mildew is one of the most common and persistent diseases affecting ornamental crops, including roses. The disease appears as a white, powdery coating on leaves, stems, and flowers. Infection can reduce plant quality by redirecting plant nutrients to the fungus, interfering with photosynthesis, and altering leaf and flower development. For commercial growers, managing powdery mildew often requires repeated fungicide applications throughout the growing season.
However, controlling the disease is becoming more challenging. Powdery mildew populations are developing resistance to the most commonly used fungicides, and some chemical options are facing increasing regulatory restrictions. As a result, new sustainable ways to protect ornamental crops from this damaging disease are required.
A research project led by Dr. Mary C. Wildermuth at the University of California, Berkeley is exploring an innovative solution: RNA-based biocontrol products designed specifically to target powdery mildew fungi. Supported by the American Floral Endowment, the project focuses on powdery mildew in roses and aims to develop a highly targeted disease management tool that could reduce reliance on traditional fungicides.
Figure: Hybrid tea rose infected with powdery mildew, with a close-up of an infected leaf, and 20X magnification showing the chains of new powdery mildew spores. Photo credit: Kai U. Wu, Wildermuth lab, UC Berkeley
RNA is a naturally occurring molecule found in all living organisms. Researchers can use specially designed RNA molecules to interfere with essential genes in a pest, preventing the pest from growing or reproducing. Because these products are designed to be highly specific to the targeted pest gene, they have the potential to affect only the intended organism with minimal impact on beneficial organisms and the environment. Recent US EPA approvals of RNA-based bioproducts for agricultural pests demonstrate growing interest in this technology.
During the first year of the project, the research team established a rose–powdery mildew system that will allow them to evaluate potential RNA treatments under controlled conditions. The team isolated powdery mildew from infected hybrid tea roses and developed greenhouse and growth chamber systems to maintain both the disease and susceptible rose varieties for testing.
A major focus of Year 1 was identifying the fungal genes that could serve as effective targets for RNA-based control. To do this, the researchers studied how the powdery mildew fungus develops and which genes become active at different stages of infection. By comparing fungal growth on plant leaves and on artificial surfaces, the team gained a better understanding of the genes that are especially important during the earliest stages of disease development.
Using this information, the researchers prioritized a group of genes that appear to be critical for the fungus’s survival, growth, and reproduction. Several of these targets are involved in how the fungus obtains nutrients and energy, while others help regulate key biological processes. Six of the selected targets have already shown promise in previous studies involving other powdery mildew species, where silencing the genes reduced fungal growth and reproduction. In addition, the team identified 15 more candidate genes for future testing.
The researchers are also working to ensure that future RNA products remain effective against different strains of rose powdery mildew. Samples have been collected from multiple locations, and additional collections will be made from commercial production sites. This information will help the team design RNA molecules that can work across a range of powdery mildew populations.
The development of disease screening assays is another important Year 1 goal for the project. These allow the researchers to evaluate whether a particular RNA treatment is able to limit powdery mildew growth and/or reproduction and to optimize application methods and treatment rates. They include spore germination/development, detached rose leaf, and whole plant powdery mildew disease assays. These studies will help identify the most promising RNA candidates before moving into larger-scale testing.
Looking ahead, the project will continue to identify and test additional gene targets while evaluating the effectiveness of RNA treatments in greenhouse settings. During the second year, researchers plan to begin testing selected RNA products in commercial floriculture environments with industry partners.
The potential impact of this work extends beyond roses. Because powdery mildew genes tend to be highly conserved across species, successful targets identified in roses could potentially be adapted for use in other ornamental crops. Some of the same targets may even prove useful for RNA-based treatment of other important ornamental diseases, such as downy mildew. In the long term, the knowledge generated through this research could also help breeders develop ornamental varieties with improved disease resistance.
As fungicide resistance continues to challenge growers, RNA-based technologies may offer a new tool for disease management that is highly targeted, environmentally compatible, and capable of protecting the quality and marketability of ornamental crops.
By Mary C. Wildermuth, UC Berkeley, and Laura Barth, AFE Research Coordinator
