Nepoviridae

Nepoviridae is a family of plant viruses characterized by bipartite genomes and nonenveloped, icosahedral virions. Members have two positive-sense RNA segments, referred to as RNA1 and RNA2, which together encode replication, movement, and coat proteins. Virus particles are small, typically about 28–30 nanometers in diameter, and replication occurs in the cytoplasm of plant cells. Gene expression involves proteolytic processing of large polyproteins and the production of a subgenomic RNA for coat protein expression.

Genome organization within Nepoviridae features RNA1 carrying replication-associated functions and RNA2 encoding movement-related and structural proteins. Each segment is encapsidated separately, and the movement protein enables cell-to-cell spread within the plant. The coat protein is encoded on RNA2 and forms the outer shell of the virion.

Hosts and disease impact: Nepoviruses infect a wide range of herbaceous and woody plants, including economically important crops such as grapevines, tomatoes, strawberries, and stone fruits. Diseases commonly associated with nepoviruses include fanleaf degeneration of grapevines and various ringspot or necrosis symptoms in other hosts. The economic impact is significant in affected production regions, particularly in viticulture and fruit crops.

Transmission and management: Most nepoviruses are transmitted semi-persistently by plant-parasitic nematodes, especially nematode vectors in the genera Xiphinema and Longidorus. Management relies on certified virus-free planting material, nematode control, crop sanitation, and, where available, resistant cultivars. Diagnostic methods include serology and molecular techniques such as RT-PCR and sequencing.

Notable members include Grapevine fanleaf virus and Tomato ringspot virus, which exemplify the agricultural importance and bipartite genome organization that define this virus family.