White rust of sweet potato

Pathogen and disease type
The causal agent of this disease is Albugo ipomoeae-panduratae, an oomycete that belongs to the group of white rust pathogens. This organism is an obligate parasite, meaning it requires living host tissue to complete its life cycle. The resulting condition, white rust, is a widespread foliar disease that disrupts the normal physiological functions of the plant.

Host plants
The primary host for this pathogen is the sweet potato (Ipomoea batatas). Additionally, various wild species within the Convolvulaceae family, such as morning glories, can act as alternative hosts. The disease is most prevalent in tropical and subtropical regions where environmental conditions are consistently favorable for pathogen growth.

Symptoms and signs of infection
The most distinct symptom is the formation of white, raised, blister-like pustules on the underside of the leaves. These pustules represent the sporangia of the pathogen. Corresponding to these spots, chlorotic yellow lesions may appear on the upper side of the leaf. In severe cases, foliage may become distorted, necrotic, and drop prematurely, leading to defoliation.

Environmental factors and damage
Development of white rust is heavily dependent on moisture. High humidity, frequent rainfall, and dew periods are critical for the dispersal of sporangia, which are primarily spread by wind and water splashes. The damage is manifested by a reduction in leaf area, reduced tuber yield, and lower overall quality of the harvest due to compromised plant health.

Protection and prevention measures
Management of white rust requires integrated pest management strategies:

• Sourcing high-quality, disease-free planting material to prevent initial outbreaks.
• Rotating crops to non-susceptible species to reduce soil-borne inoculum.
• Removing and destroying weeds in the Convolvulaceae family that harbor the pathogen.
• Applying protective fungicides during wet weather conditions when infection risk is high.
• Improving field sanitation to minimize the buildup of inoculum throughout the growing season.