Molecular Characterization and Phylogenetic Analysis of Tobacco Streak Virus Isolates in Sunflower and Soybean

Abstract

Molecular characterization and phylogenetic analysis of Tobacco streak virus (TSV) isolates infecting sunflower (Helianthus annuus L.) and soybean (Glycine max L.) were undertaken to determine genetic variability and evolutionary relationships among field populations. Symptomatic leaf samples exhibiting chlorotic streaks, necrosis, and mosaic patterns were collected from major oilseed-growing regions and subjected to reverse transcription polymerase chain reaction (RT-PCR) using TSV-specific primers targeting coat protein and movement protein genes. Amplified products confirmed the presence of TSV in both hosts, indicating natural cross-host infection under field conditions. Sequencing of representative isolates revealed nucleotide substitutions and amino acid variations among sunflower- and soybean-derived isolates, suggesting host-associated genetic differentiation. Phylogenetic reconstruction grouped all isolates within the TSV clade, closely related to previously reported strains from Asia and other oilseed-producing regions, indicating global genetic continuity with regional diversification. Pairwise sequence comparisons showed moderate genetic variability, reflecting ongoing evolutionary pressure possibly driven by host adaptation and vector-mediated transmission dynamics. No clear host-specific clustering was observed, although minor sub-grouping suggested limited geographic structuring. The conserved nature of key functional genomic regions supports the stability of TSV populations, while observed polymorphisms highlight their adaptive potential. The study confirms TSV as an emerging constraint in oilseed production systems affecting multiple hosts and underscores the importance of molecular surveillance for accurate diagnosis and epidemiological tracking. Early detection and characterization of viral diversity are essential for developing effective management strategies, including the deployment of virus-free planting material, vector control, and breeding for resistance. These findings contribute to a better understanding of TSV population structure and its epidemiological significance in sunflower and soybean agroecosystems.