Potato purple-top

Potato purple-top is a significant plant disease caused by phytoplasmas, which are specialized wall-less prokaryotes that colonize the phloem tissue of the host plant. By disrupting the transport of photosynthates from leaves to roots and tubers, the pathogen causes systemic stress that leads to severe physiological decline in the potato crop.

The host range of this disease is extensive, encompassing various Solanaceae crops such as tomatoes, peppers, and eggplants, as well as many common agricultural weeds. These weeds serve as crucial reservoirs for the phytoplasma, allowing the disease to persist in an area even in the absence of potato cultivation.

Key symptoms of the disease include the characteristic purpling or reddening of the leaf margins, particularly at the top of the plant, accompanied by upward curling and chlorosis. Infected plants often show stunted growth, proliferation of axillary shoots, and the production of small, misshapen tubers that may exhibit thread-like sprouting when stored.

The transmission of the disease is strictly dependent on insect vectors, primarily leafhoppers. These insects acquire the phytoplasma by feeding on infected plants and then transmit it to healthy ones during subsequent feeding sessions. The prevalence of the disease is strongly correlated with the population density and movement of these vectors during warm, dry growing seasons.

Management of Potato purple-top relies on an integrated approach since the disease cannot be controlled by chemicals once the plant is infected. Recommended strategies include:

• Sourcing high-quality, certified pathogen-free seed tubers.
• Implementing effective insecticide programs to reduce leafhopper populations in and around fields.
• Managing weed populations to minimize primary inoculum sources.
• Rogueing and destroying symptomatic potato plants as soon as they are identified to prevent secondary spread.