Tomato yellows

Tomato yellows is a viral disease caused by the Crinivirus flavisolani pathogen, which significantly impacts solanaceous crops. As a member of the Crinivirus genus, this virus is phloem-limited, meaning it restricts its replication and movement to the plant's vascular tissue. This localization is the primary reason for its characteristic systemic symptoms throughout the plant.

The primary host for this pathogen is the tomato plant (Solanum lycopersicum). However, it can also infect other related solanaceous species, which often act as silent reservoirs in the vicinity of production sites. These secondary hosts are crucial for the survival of the virus during the off-season when tomato crops are not being actively grown.

Symptoms of the infection typically begin as interveinal chlorosis on the lower leaves. As the disease progresses, these yellowing patches expand, and the leaves may thicken, become brittle, or curl downwards. Unlike nutrient deficiencies, these symptoms are caused by the disruption of nutrient transport, leading to stunted overall plant growth and diminished fruit development.

The spread of Crinivirus flavisolani in the field and greenhouses is mediated by whitefly vectors, specifically Trialeurodes vaporariorum and Bemisia tabaci. The transmission is semi-persistent, meaning the whitefly acquires the virus by feeding on an infected plant and can transmit it for several days. High temperatures and high population densities of whiteflies are the primary drivers of rapid viral spread.

The economic impact of this virus can be severe, leading to reduced marketability and significant yield loss. Management strategies focus on breaking the disease cycle through:

• strict management of whitefly populations using biological and chemical controls
• the implementation of physical barriers like fine-mesh insect screening in greenhouses
• the removal and destruction of symptomatic plants
• sanitation practices to eliminate weeds that host the virus and the vectors