Understanding powdery mildew in pepper crops
Five questions to Beste Kanli, Specialist Phytopathology
Beste Kanli works as a Specialist Phytopathology at Rijk Zwaan. In this role, she focuses on understanding plant diseases and how they interact with crops such as pepper. As a phytopathology specialist, she studies how pathogens infect plants, how diseases develop and spread, and how crops can be better protected through breeding and innovative solutions.
Her work is closely linked to Rijk Zwaan’s efforts in developing resistance against powdery mildew (Leveillula taurica, Lt) in pepper. By combining scientific insight with practical crop knowledge, Beste contributes to the development of varieties that help growers manage disease pressure and achieve more stable production.
We asked Beste five key questions to better understand how this disease develops and how growers can stay in control.
#1 What is powdery mildew in pepper?
“Powdery mildew, caused by Leveillula taurica, is one of the most important diseases in greenhouse pepper cultivation and affects a wide range of host plants.
Unlike most powdery mildew pathogens, this fungus develops largely inside the leaf tissue during the early stages of infection.”
“The first signs of powdery mildew are often subtle, with light yellow spots on the upper leaf surface. Only later do the white fungal colonies become visible on the underside. By that stage, the infection is often already well established, which can lead to leaf loss, reduced photosynthesis and, ultimately, yield reduction. That is why regular monitoring of older, lower leaves is so important.”
#2 How does the life cycle of the fungus proceed, and what are favourable conditions for the fungus?
“The disease cycle of Leveillula taurica starts when airborne spores (conidia) land on the leaf surface. Under favourable conditions, they germinate quickly and grow towards the stomata (pores).”
“The fungus enters the plant through these natural openings and develops within the leaf tissue, where it feeds on living plant cells. This internal phase can last several weeks before visible symptoms appear, making early intervention challenging.
Eventually, the fungus emerges again through the stomata to form the characteristic white colonies and produce new spores.”
The pathogen thrives under typical greenhouse conditions:
Moderate temperatures (20–25°C)
Fluctuating humidity (humid nights and drier days)
Dense crops with limited air circulation
While high humidity supports infection and internal development, spore dispersal is mainly enhanced under drier conditions with air movement. Temperatures above 30°C generally slow disease development.
#3 How does the fungus spread?
“Powdery mildew mainly spreads through airborne spores. These move easily via wind and greenhouse air currents, allowing the disease to spread quickly within and between crops.”
Additional factors that contribute to spread include crop handling (workers and tools), infected plant material and alternative host plants, such as weeds.
Dry conditions with active air circulation favour dispersal, while humid conditions promote successful infection, making the disease highly adaptive to greenhouse environments.
#4 How does the fungus infect the plant? Which plant parts are infected?
Leveillula taurica differs from many other powdery mildew fungi because it infects plants through the stomata, rather than directly penetrating the leaf surface.
Once inside the plant the fungus develops within the leaf tissue. It extracts nutrients from living plant cells and establishes internal fungal growth before becoming visible.
The disease primarily affects leaves, especially older and lower leaves. The underside of leaves, where sporulation is most visible.
Fruits and roots are generally not infected. This makes targeted scouting of the lower leaves particularly important for early detection.
#5 Which methods are used to study the fungus?
In practice, growers monitor powdery mildew through regular scouting. Key indicators include yellow leaf spots and white fungal growth on the underside of leaves. Disease severity is assessed based on how symptoms develop and spread within the crop.
In research and breeding programmes, more advanced techniques are used, such as microscopy to study infection processes, and molecular tools like PCR to detect early, symptomless infections.
These methods help deepen understanding of the disease and support the development of improved resistance and management strategies contributing to more reliable and sustainable pepper production.
Working together towards resilient pepper crops
At Rijk Zwaan, tackling challenges like powdery mildew is a collaborative effort. By combining scientific expertise, breeding innovation and close cooperation with growers, we continue to develop solutions that enhance crop resilience and productivity.
Through initiatives such as Lt Defense™, and the dedication of specialists like Beste Kanli, Rijk Zwaan helps growers stay one step ahead, ensuring healthier crops and more stable production in an ever-changing environment.
Picture: comparison of infected and healthy leaves.