Orthotospovirus

Orthotospoviruses (genus Orthotospovirus) represent a significant group of plant viruses that cause severe systemic diseases in a vast array of horticultural and agronomic crops. These viruses are global in distribution and are known for their ability to break down traditional plant defenses, leading to substantial yield losses in tomatoes, peppers, lettuce, and numerous ornamental plants.

The causative agent belongs to the Tospoviridae family. A defining characteristic of these viruses is their exclusive transmission via thrips, particularly the western flower thrips (Frankliniella occidentalis). The virus is acquired by larvae feeding on infected plant tissues and is subsequently transmitted by adult insects, which remain infectious for the remainder of their lifespans.

Symptoms of an Orthotospovirus infection are highly variable and often resemble nutrient deficiencies or other biotic stressors. Common signs include chlorotic or necrotic spots, ringspot patterns on leaves, stem necrosis, and severe stunting of plant growth. In many cases, infected plants exhibit distorted foliage and poor fruit set, which significantly impacts both the quality and quantity of the harvest.

Disease development is heavily dependent on the presence of thrips and favorable environmental conditions. High temperatures and humidity accelerate the lifecycle of the vector, leading to rapid disease spread within greenhouses and fields. During the off-season, the virus survives in alternative weed hosts, which act as initial reservoirs for the pathogen when the new growing season begins.

Since there is no cure for plants once infected with an Orthotospovirus, management must focus on strict preventative strategies. Controlling the vector and eliminating infection sources are the primary objectives for growers:

• Implementing comprehensive integrated pest management (IPM) to control thrips populations.
• Sanitation practices, including the removal of infected plants and surrounding weeds.
• Utilizing resistant or tolerant cultivars where available in seed catalogs.
• Installing physical barriers such as insect-proof netting in greenhouses.
• Conducting regular viral testing of nursery stocks to ensure disease-free inputs.