Tomato spotted wilt virus (TSWV) is a widespread and challenging plant disease affecting many crops and ornamental plants worldwide. It is a persistent concern for gardeners and commercial growers due to its broad host range and the difficulty in managing its spread.
Understanding Spotted Wilt Virus
Tomato spotted wilt virus (TSWV) is caused by an Orthotospovirus, a type of plant virus belonging to the Tospoviridae family. TSWV is considered one of the most economically damaging plant viruses worldwide, causing significant losses in agricultural production.
The virus is systemic, meaning it infects the entire plant once introduced, spreading throughout its tissues. It has an exceptionally wide host range, infecting over 1,000 different plant species across 85 families, including both broadleaf plants and grasses.
Recognizing Symptoms and Host Plants
The symptoms of spotted wilt virus are highly variable, depending on the specific plant species infected, the virus strain, and environmental conditions. Common indicators include bronzing or purpling of leaves, particularly on younger foliage, often accompanied by small, dark lesions. Infected leaves may also show yellowing, mosaic patterns, or distinctive concentric ringspots.
Plants often exhibit stunted or distorted growth, and entire leaves may brown, roll, and wilt despite adequate moisture. Necrotic lesions can develop on leaves and stems, sometimes causing dieback of growing tips. On fruits, symptoms can manifest as yellow or brown ringspots, sunken areas, discoloration, or deformities.
Many common plants are susceptible to TSWV. Important agricultural hosts include tomatoes, peppers, tobacco, lettuce, peanuts, and potatoes. Ornamental plants like impatiens, dahlias, chrysanthemums, and begonias are also frequently affected. Additionally, numerous weed species can harbor the virus, serving as reservoirs for both the virus and its insect carriers.
How the Virus Spreads
Tomato spotted wilt virus is primarily transmitted by thrips, small, slender insects belonging to the order Thysanoptera. The Western flower thrips (Frankliniella occidentalis) is the most efficient and globally prevalent vector, though at least 10 different thrips species can transmit the virus. Thrips acquire the virus by feeding on an infected plant during their larval stage.
The virus then replicates within the thrips’ bodies. Once infected, adult thrips can transmit the virus to healthy plants throughout their remaining lifespan, but only if they acquired it during their larval stage.
TSWV is generally not spread by touching infected plants, pruning tools, or seeds. While thrips are not strong fliers, they can be carried long distances by wind currents, facilitating widespread virus transmission.
Management and Prevention Strategies
Managing spotted wilt virus involves a multi-pronged approach, as there is no cure for an infected plant. Removing and destroying infected plants promptly is a primary step to prevent further spread within a growing area. Vigilant weed control in and around cultivation areas significantly reduces potential virus reservoirs, as many weeds can host both the virus and thrips.
Controlling thrips populations is important for preventing TSWV. Cultural practices such as using reflective mulches can deter thrips from landing on plants, reducing infection rates. Biological controls, including the release of predatory mites or beneficial nematodes, can help suppress thrips numbers. Insecticides can be used, but resistance development in thrips necessitates rotating different chemical classes and applying them strategically, often preventively, as treatments after symptoms appear are often ineffective.
Selecting and planting varieties of susceptible crops with known genetic resistance to TSWV is a highly effective prevention method. For instance, tomato varieties with the Sw-5 gene offer resistance. Regular monitoring of plants for both thrips presence using sticky traps and early symptoms of the virus allows for timely intervention. In enclosed environments like greenhouses, physical barriers such as fine mesh screening on vents and doorways can exclude thrips.