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TECHNICAL SESSION: Virus discovery and virus populations

Identification of a new member of the family Phenuiviridae, order Bunyavirales, associated with lettuce dieback disease
William Wintermantel - USDA-ARS. Laura Hladky- USDA-ARS, Steven Koike- TriCal Diagnostics, Dimitre Mollov- USDA

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 is traditionally known 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 several symptomatic fields and leaves were used to mechanically transmit infectious agents to an array of test plants, resulting in symptoms indicative of a virus but distinct from those caused by TBSV or MPV. High throughput sequencing of RNA extracts from symptomatic lettuce field samples and Nicotiana benthamianatest plants consistently identified a virus with 31-36% homology to a virus recently characterized from watermelon, associated with the family Phenuiviridae, order Bunyavirales. Primers were developed to a portion of the polymerase protein, and RT-PCR analysis of archived field samples indicates association of the new virus with plants exhibiting lettuce dieback symptoms. Continuing molecular and biological studies are characterizing the genome of the new virus and its involvement in LDD disease development.