Orthotospovirus

Orthotospovirus is a genus of viruses belonging to the family Bunyaviridae. These viruses are known to cause significant plant diseases, affecting a wide range of crops worldwide, leading to substantial economic losses in agriculture. Orthotospoviruses are unique among plant viruses due to their segmented, negative-sense, single-stranded RNA genomes, which are encapsulated within a spherical viral envelope. This genus includes several important pathogens, such as the Tomato spotted wilt virus (TSWV), which was the first member to be identified and remains one of the most studied and economically damaging species.

Biology

Orthotospoviruses are transmitted by thrips, which are tiny insects capable of carrying the virus from infected to healthy plants. The relationship between thrips and Orthotospoviruses is specific, with certain virus species being transmitted by specific thrips species. This specificity plays a crucial role in the epidemiology of the diseases caused by these viruses.

The genome of Orthotospoviruses is divided into three segments, known as Large (L), Medium (M), and Small (S), each encoding for different viral proteins. The L segment encodes the RNA-dependent RNA polymerase necessary for viral replication. The M segment encodes for two glycoproteins, Gn and Gc, which are involved in virus attachment to host cells and subsequent entry. The S segment encodes for the nucleocapsid protein and a nonstructural protein, which has been implicated in the suppression of host plant defense mechanisms.

Disease Management

Managing diseases caused by Orthotospoviruses involves an integrated approach combining cultural, biological, and chemical strategies. Cultural practices include crop rotation, removal of infected plant material, and the use of reflective mulches to deter thrips. Biological control involves the use of natural predators or parasitoids of thrips. Chemical control, while effective, requires careful consideration to prevent the development of resistance in thrips populations and to minimize environmental impact.

Economic Impact

The economic impact of Orthotospoviruses is significant, with losses occurring in both field-grown and greenhouse crops. Tomato spotted wilt virus, in particular, has a broad host range, affecting over 1,000 plant species across various families. The global distribution of the virus and its vectors, coupled with the ability of the virus to infect multiple crops, exacerbates the economic damage.

Research and Future Directions

Research on Orthotospoviruses focuses on understanding the virus-thrips-plant interaction, developing resistant plant varieties, and improving disease management strategies. Advances in molecular biology and genetics offer promising tools for the development of resistant crop varieties and for the precise targeting of the virus and its vectors.