Lettuce dieback

Authors: Wintermantel, William - Bill

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 4/2/2016
Publication Date: 7/20/2017
Citation: Wintermantel, W.M. 2017. Lettuce dieback. In: Subbarao, K.V., Davis, R.M., Gibertson, R.L., Raid, R.N., editors. Compendium of Lettuce Diseases and Pests. 2nd edition. St. Paul, MN: APS Press. p. 80-81.

Interpretive Summary: Two related viruses, Tomato bushy stunt virus (TBSV) and Moroccan pepper virus (MPV) cause a disease known as lettuce dieback in California and Arizona. Lettuce dieback is characterized by yellowing, necrosis, stunting and death of lettuce plants, and often occurs in low lying areas with poor drainage, in areas near rivers, on recently flooded land. Fields with lettuce dieback often consist of plants of different sizes and stages of symptom development. Diseased plants may be either clustered or scattered in fields, and healthy plants can be found adjacent to diseased plants. Both viruses have also been found associated with a disease called escarole yellows in the eastern U.S. Lettuce symptoms are predominantly found on non-crisphead (iceberg type) lettuces due to a source of resistance universally introduced into crisphead lettuce in the 1940s. Both TBSV and MPV are members of the genus, Tombusvirus. Virus particles are isometric with a diameter of approximately 30 nm in diameter. Each virus particle contains a single molecule of RNA. The natural host range of both viruses is relatively narrow among agricultural crops. TBSV is known to infect a wide range of experimental hosts, but most experimental hosts do not become infected systemically. Less is known of the host range of MPV, although in addition to lettuce, natural infections of escarole, tomato, pepper, eggplant and pelargonium have been confirmed. There appears to be a substantial environmental component to development of lettuce dieback disease symptoms in lettuce grown in fields with a history of TBSV or MPV. All modern iceberg type lettuces carry the dominant resistance gene, Tvr1, a highly stable source of resistance that has been present in most iceberg type lettuces since the 1940s, although the gene itself was not characterized until much later. An increasing number of romaine, leaf, and other specialty lettuces also now carry this gene, which provides stable resistance to both TBSV and MPV.

Technical Abstract: Two related viruses, Tomato bushy stunt virus (TBSV) and Moroccan pepper virus (MPV) cause a disease known as lettuce dieback in California and Arizona. Lettuce dieback is characterized by yellowing, necrosis, stunting and death of lettuce plants, and often occurs in low lying areas with poor drainage, in areas near rivers, on recently flooded land. Fields with lettuce dieback often consist of plants of different sizes and stages of symptom development. Diseased plants may be either clustered or scattered in fields, and healthy plants can be found adjacent to diseased plants. Both viruses have also been found associated with a disease called escarole yellows in the eastern U.S. Lettuce symptoms are predominantly found on non-crisphead (iceberg type) lettuces due to a source of resistance universally introduced into crisphead lettuce in the 1940s. Both TBSV and MPV are members of the genus, Tombusvirus. Virus particles are isometric with a diameter of approximately 30 nm in diameter. Each virus particle contains a single molecule of RNA. The natural host range of both viruses is relatively narrow among agricultural crops. TBSV is known to infect a wide range of experimental hosts, but most experimental hosts do not become infected systemically. Less is known of the host range of MPV, although in addition to lettuce, natural infections of escarole, tomato, pepper, eggplant and pelargonium have been confirmed. There appears to be a substantial environmental component to development of lettuce dieback disease symptoms in lettuce grown in fields with a history of TBSV or MPV. All modern iceberg type lettuces carry the dominant resistance gene, Tvr1, a highly stable source of resistance that has been present in most iceberg type lettuces since the 1940s, although the gene itself was not characterized until much later. An increasing number of romaine, leaf, and other specialty lettuces also now carry this gene, which provides stable resistance to both TBSV and MPV.