Field distribution and disease incidence of tomato chlorotic spot virus, an emerging virus threatening tomato production in South Florida

Tomato chlorotic spot tospovirus is a species of the genus Orthotospovirus, family Tospoviridae. One of the causal agents of tomato spotted wilt, tomato chlorotic spot virus (TCSV) was first detected in tomato and bell pepper in south Florida in 2012 and is considered an emerging virus to the region. It has caused significant losses to tomato growers in the region since 2014. Field surveys were conducted in tomato fields in Miami-Dade County in the 2015–2016 and 2016–2017 growing seasons. Results of the surveys indicate that TCSV is the predominant virus among the three known orthotospoviruses [tomato spotted wilt virus (TSWV), groundnut ringspot virus (GRSV) and TCSV] present in south Florida. TCSV was detected in 43.8% of symptomatic samples collected in the 2016–2017 season. Mixed infection with two orthotospoviruses ranged from 2.8–6.3%, and 2.0% of the symptomatic samples were infected with all three viruses. The distribution pattern of TCSV-infected plants in a commercial tomato field in Homestead, FL suggested that the initial source of TCSV could be ornamental crops in adjacent nurseries. Up to 56.0% of the tomato plants with symptoms were observed in this field adjacent to ornamental nurseries, whereas the incidence gradually decreased to zero in the other side of the same field. Phylogenetic analysis using partial sequences of TCSV isolates revealed genetic diversity of 2.0% or less at the nucleotide level.