Potato spindle tuber viroid

The causal agent is the Potato spindle tuber viroid (PSTVd), a small, circular, single-stranded RNA molecule that lacks a protein coat. This pathogen is highly infectious and systemically colonizes its host plants, hijacking cellular machinery to replicate, which results in metabolic disorders within the plant tissue.

The disease primarily impacts potatoes and tomatoes, but its host range also includes other Solanaceous species such as peppers, eggplants, and various ornamental plants. Because many weeds and wild relatives can act as asymptomatic carriers, the pathogen can persist in an environment long after a commercial crop has been harvested.

Infected potato plants exhibit distinct symptoms, including stunted growth, upright foliage, and smaller leaves. The most characteristic sign is the appearance of tubers that are elongated, spindle-shaped, or cylindrical, often accompanied by prominent "eyes" or cracking on the surface, which drastically reduces the marketability of the produce.

The transmission of the viroid occurs primarily through mechanical injury. Farming activities such as mechanical harvesting, pruning, and cutting seed tubers are major pathways for spread. Insects, including aphids and leafhoppers, may also facilitate transmission, while seed and pollen transmission add further complexity to managing this persistent pathogen.

Economic damage is substantial, often leading to total loss of seed certification status and significant yield reductions. Control relies on strict biosecurity measures: using certified pathogen-free seeds, disinfecting tools with appropriate chemicals, strictly controlling weeds, and promptly roguing out any plants displaying signs of the infection to prevent field-wide contamination.