Population analysis on tomato spotted wilt virus isolates inducing various symptoms on tomato, pepper, and Chenopodium album in Turkey

Molecular identification of tomato spotted wilt virus (TSWV) has been conducted in several surveys in Turkey, but the population structure of the virus in the country remains unknown. During 2019-2020, 227 viral symptomatic tomato (Solanum lycopersicum), pepper (Capsicum annuum), and weeds leaf samples were collected from Ankara, Bartin, Eskisehir, Konya, and Zonguldak provinces. RT-PCR tests confirmed TSWV infection in 99 tomato, pepper, and Chenopodium album samples (43.6%). Phylogenetic analysis based on complete nucleotide sequences of N gene clustered the 23 newly sequenced Turkish isolates and other 281 isolates in NCBI GenBank into three major clades: p202/3WT, Tarquinia, and p105. All tested Turkish isolates were included in either p202/3WT or p105 clade. Global isolates retained high nucleotide and amino acids identity for N gene according to percentage identity analysis. N gene of TSWV was under very strong negative selection pressures, as shown by the very low omega values (<0.15) for all analyzed populations. Three neutrality tests also suggested that these populations are undergoing balancing selection by assigning negative values to most of them. The genetic differentiation and gene flow analysis among three clades demonstrated that they are genetically divergent from each other, but their medium FST values of around 0.5 showed that gene flows among clades are rare. This is the first detailed study on the genetic diversity and population structure of TSWV in Turkey.