Vertical transmission of tomato viruses: A hidden threat to global seed trade

Vertically transmitted viruses can severely reduce yield and plant vigour, causing smaller fruits, poor quality, or complete crop loss. Marketable yield often declines due to blemishes and deformities, while indirect costs arise from biosecurity measures and phytosanitary controls, such as EU regulations for ToBRFV.

The significance of vertical transmission varies by production system. In temperate regions, growers produce tomatoes typically in protected environments like glasshouses or plastic tunnels, often using hydroponics. These systems allow vector control but involve frequent handling, which increases the risk of mechanically transmitted pathogens such as tobamoviruses (ToBRFV). On the other hand, field-grown tomatoes in warmer climates face greater pressure from insect-transmitted viruses like whitefly-borne begomoviruses (ToLCNDV, TYLCV).

Global seed production adds complexity, as companies grow seeds in multiple regions to meet market demand. Labor-intensive practices such as emasculation and pollination in hybrid seed production create frequent opportunities for contamination. Additionally, seed-borne infections can reduce seed viability, germination, and fruit quality. While early infections often cause severe damage, later infections may result in larger fruits with fewer necrotic seeds. Studies show that timing of infection strongly influences seed health and crop performance.

Economic impacts remain poorly quantified, as most trials compare artificially inoculated plants with controls rather than simulating season-long outbreaks. For example, PepMV studies in UK glasshouses reported no overall yield loss but significant downgrading of fruit quality, while ToBRFV outbreaks caused severe crop damage globally.