Biology, phylogenetic and evolutionary relations of Tradescantia mild mosaic virus isolates from Hungary

In Western Transdanubia in 2018 and in Central-Hungary in 2022 spiderwort plants showed flower breaking symptoms and mild mosaic on the foliage, which indicated a potential virus infection. One gram of symptomatic leaf sample was collected at both locations. Potyvirus-specific ELISA tests demonstrated potyvirus infection. To identify the virus species, potyvirus-specific RT-PCR was carried out on the samples. In both samples specific PCR products were detected and cloned into pGEM®-T Easy vector. The nucleotide sequences of the inserts were determined by Sanger sequencing. BLASTn searches on the complete coat protein region of both isolates demonstrated more than 99.87% identity with Tradescantia mild mosaic virus (TraMMV; accession number OL584375). Koch postulates were fulfilled by sap inoculating seed grown spiderwort plants. Phylogenetic analyses of the TraMMV coat protein sequences revealed two distinct evolutionary lineages: a tropical subgroup with at least 97.84% identity within the group and temperate subgroup with at least 98.97% identity within the group. One major difference between the subgroups was in the triplet responsible for vector transmission. The isolates belonging to the tropical subgroup had DAG triplets, while the temperate subgroup had NAG triplets. The difference in the triplets could be caused by natural diversification, directional selection or disruptive selection.

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