White rust of sweet potato

Taxonomy and nature of the pathogen: Albugo ipomoeae-panduratae belongs to the kingdom Chromista, phylum Oomycota (oomycetes), and the family Albuginaceae. Often mistakenly grouped with fungi, this organism is actually an oomycete, functioning as an obligate parasite that specifically targets plants within the Convolvulaceae family.

Host plants and symptoms: The primary host of economic importance is the sweet potato (Ipomoea batatas), though the pathogen also affects various morning glory species. The disease is characterized by the formation of small, raised, white to cream-colored pustules, primarily on the undersides of leaves. These pustules represent erupting sporangia, often accompanied by chlorotic spots on the upper leaf surface.

Biology and life cycle: This pathogen spreads through motile zoospores that require free moisture on the leaf surface to germinate and penetrate the host tissue. The cycle is completed by the formation of thick-walled oospores, which allow the pathogen to survive in soil and plant debris, providing the inoculum source for future infection cycles when conditions become favorable.

Conditions for development and impact: Disease outbreaks are favored by cool, moist conditions and high humidity, which facilitate spore dispersal and germination. Severe infections lead to significant defoliation, which reduces the photosynthetic area of the plants. This directly results in stunted growth and a considerable reduction in both the size and market quality of the harvested storage roots.

Control and management: Management strategies include the use of disease-free propagation material and strict sanitation, such as removing infected crop residues and weeds that serve as alternate hosts. Crop rotation is essential to break the infection cycle. In intensive cultivation, application of contact or systemic fungicides targeting oomycetes may be necessary to manage the disease during periods of high humidity.