Viruses infecting Solanaceous Crops

Robert L. Gilbertson Department of Plant Pathology University of California-Davis ID: A striking diversity of have evolved to infect plants Understanding the biology of the virus is necessary for effective disease management

• Properties of the virus (virion structure and genetic material) • Host range • Vector (insect or other) • Sources of inoculum -seed -weeds/other reservoir hosts -old crops -insects • Means of survival in the absence of the economic hosts Key viruses that infect and pepper

• ( mosaic and Pepper mild mottle) • Potexvirus (Pepino mosaic virus) • Cucumovirus (Cucumber mosaic virus) • Potyvirus (Potato virus Y, Tobacco etch, Pepper mottle) • Tospovirus (Tomato spotted wilt virus) • Closterovirus (Tomato chlorosis virus, Tomato infectious chlorosis) • Geminivirus (Tomato severe leaf curl, Pepper huasteco yellow vein virus, Tomato Havana virus, Pepper golden mosaic virus and others) • Others: Tomato bushy stunt, Alfalfa mosaic, Tobacco streak and Tomato necrotic spot • New: torrado viruses Key viruses that infect tomato and pepper • Family/group: • Tobacco and tomato mosaic (TMV)/ Pepper mild mottle virus (PMMV) • Particle: rigid rod • Genetic material: RNA • Vector: None (mechanically transmitted) • Inoculum sources: -On seed (treat with

10% Na3PO4 2 hrs) -Crop debris -Benches, stakes, trays -Humans • Host range: Narrow (tomato/pepper) Key viruses that infect tomato and pepper • PMMV can be very serious on pepper and ToMV on tomato in field and greenhouse • Symptoms include mottling and yellow/ green mosaic on leaves and small, malformed fruits • Highly infectious and easily spread by contact • Seedborne probably on seed coat with virus spread to plants during transplanting and other cultural practices • Control: Resistance, seed treatment (TSP for 1-2.5 hours), sanitation, roguing rotation Key viruses that infect tomato and pepper • Family/group: Potexvirus • Pepino mosaic virus • Particle: flexous rod • Genetic material: RNA • Vector: None (mechanically transmitted) • Inoculum sources: -On seed (?) -Crop debris -Benches, stakes, trays -Humans • Host range: Narrow (tomato, potato and tobacco) Key viruses that infect tomato and pepper • First IDed in 1974 in Peru • In 1990s appeared in greenhouse tomatoes in and US • Symptoms vary depending on strains • Includes mosaic/mottle and fruit blotching and marbling • Highly infectious and easily spread by contact • Seedborne but some question about this • May be very low level of seed contamination on the seed coat • Control requires strict sanitation • Cross protection has been used Key viruses that infect tomato and pepper

• Family/group: Cucumovirus • Cucumber mosaic virus (CMV) • Particle: spherical • Genetic material: RNA • Vector: Aphids (non-persistent) • Inoculum sources: -Weeds and other reservoir hosts -Crops in old fields -Aphids -Not seedborne in tomato or pepper • Host range: Wide (tomato/pepper/ cucurbits/beans and many others) Key viruses that infect tomato and pepper • Family/group: Potyvirus • Potato virus Y (PVY), Tobacco etch (TEV), Pepper mottle (PeMV) • Particle: flexous rod • Genetic material: RNA • Vector: Aphids (non-persistent) • Inoculum sources: -Weeds other reservoir hosts -Crops in old fields -Aphids -Not seed-transmitted • Host range: Relatively narrow (tomato/pepper) Key viruses that infect tomato and pepper • Family/group: Tospovirus • Tomato spotted wilt virus • Particle: large spherical • Genetic material: RNA • Vector: Thrips (persistent propagative) • Inoculum sources: -Weeds other reservoir hosts -Crops in old fields -Thrips -Not seed-transmitted • Host range: Wide (tomato/pepper and many other crops, weeds, ornamentals) Key viruses that infect tomato and pepper

• Family/group: Closterovirus • Tomato chlorosis virus and Tomato infectious chlorosis • Particle: large flexous rods • Genetic material: RNA • Vector: Whiteflies (semi-persistent) • Inoculum sources: -Weeds other reservoir hosts -Crops in old fields -Whiteflies -Not seed-transmitted • Host range: Narrow Geminiviruses

• Family Geminiviridae

• Twinned icosahedral virions (18 x 30 nm) • Circular ssDNA genome (2.8-5.5 kb) Genera of the Family Geminiviridae

Mastrevirus Topocuvirus Curtovirus Begomovirus

Genome A B

Vector Leafhopper Treehopper Leafhopper WhiteflyWhitefly

Host

Dicots Dicots Monocots Dicots Family Geminiviridae is composed of seven genera

Becurtovirus Genus Begomovirus Curtovirus Mastrevirus Turncurtovirus Eragrovirus β Topocuvirus

Genome A B

Vector

Whiteflies Beet leafhopper Leafhoppers (Bemisia tabaci) (Circulifer tenellus)

Host (Eragrovirus)

Dicots Dicots Monocots/ Dicots NW and OW Distribution NW and OW NW and OW Only OW Only OW Only NW Tomato begomoviruses

• >60 different begomovirus species infect tomato worldwide • All are transmitted by Bemisia tabaci • They are not seed- or mechanically (by touch) transmitted • Have relatively narrow host ranges, usually within the (tomato family) • Cause similar symptoms including stunted and distorted growth; leaf curl, crumple, distortion, mosaic/mottle and yellowing • Cause considerable yield losses, particularly when plants are infected at an early stage of growth Emergence of new diseases in Spain, Mexico and Central America • Referred to as ‘torrado’ (burned) in Spain, ‘mancha de chocolate’ (chocolate spot) in Guatemala and ‘marchitez’ in Mexico • Characterized by a mottling and crumpling of leaves followed by necrosis of leaves, stems and fruits (less common) • Caused by a new type of RNA virus: torradovirus that is transmitted by whiteflies • Evidence of seed transmission? • Would explain how these viruses have recently appeared in many areas