Potato spindle tuber viroid

The Potato spindle tuber viroid (PSTVd) is a devastating plant pathogen recognized globally as a significant threat to solanaceous crops. Historically researched in relation to its impact on wild Peruvian tomato species and domestic cultivars, it is classified as a small, circular, non-coding RNA molecule.

Taxonomically, the agent is placed in the genus Pospiviroid, family Pospiviroidae. Unlike traditional viruses, it lacks a protein coat and relies entirely on the host plant's replication machinery. This simplicity allows it to accumulate in high concentrations within the host, leading to systemic infection.

The primary symptom on tomatoes is the development of spindly or stunted growth, accompanied by leaf curling and yellowing. The fruits are often smaller, deformed, and may exhibit uneven ripening. In potatoes, the characteristic symptom is the formation of elongated, spindle-shaped tubers with cracked skin, significantly reducing the market value.

Environmental conditions, particularly warm temperatures, facilitate rapid replication and movement of the viroid within the plant tissues. The infection is primarily spread through vegetative propagation, contaminated tools, and physical contact between plants. It can also be transmitted via infected pollen or seeds in some cultivars.

Management of PSTVd requires a strict biosecurity approach. Because there are no chemical pesticides to cure infected plants, control relies on prevention. This includes the use of certified pathogen-free seeds, rigid sanitation protocols for equipment, and the removal and destruction of infected host plants to prevent the further spread of the viroid throughout the field or greenhouse.