Identification of additional viruses contributing to lettuce dieback disease

Authors: Wintermantel, William - Bill

Submitted to: Meeting Abstract
Publication Type: Other
Publication Acceptance Date: 3/31/2021
Publication Date: 3/31/2021
Citation: Wintermantel, W.M. 2021. Identification of additional viruses contributing to lettuce dieback disease. California Leafy Greens Research Program Annual Meeting, March 31, 2021 (virtual).

Interpretive Summary:

Technical Abstract: Lettuce dieback disease (LDD) causes foliar necrosis, stunting, and death of lettuce plants throughout all western US lettuce production regions. The disease is more prevalent in poorly drained soils and was traditionally believed to be caused by either of two viruses from the genus Tombusvirus: Tomato bushy stunt virus (TBSV) and Moroccan pepper virus (MPV). However, in recent years, neither tombusvirus has been found in symptomatic plants collected from the field, nor have degenerate primers detected any divergent tombusviruses from diseased lettuce. To identify additional viruses that may be associated with LDD, lettuce samples were collected from symptomatic fields and leaves were used to mechanically passage infectious agents to an array of test plants, resulting in symptoms in N. benthamiana distinct from those caused by TBSV or MPV. High throughput sequencing of RNA extracts from symptomatic lettuce field samples and Nicotiana benthamiana test plants consistently identified a previously unknown ssRNA virus with a tripartite RNA genome distantly related to others in the family Phenuiviridae, order Bunyavirales. RT-PCR using primers designed to a portion of the polymerase gene identified the new virus in nearly all symptomatic field samples and in archived diseased lettuce samples dating to 1999. The new virus, lettuce dieback associated virus (LDaV) has been reintroduced from infected N. benthamiana to lettuce and reproduced LDD symptoms. Additional experiments are needed for to determine if the virus has a biological vector.