Characterization of potato spindle tuber viroid isolates (Pospiviroid fusituberis) occurrence on tomato plants in Russia

This work reports the first detection of potato spindle tuber viroid (PSTVd) on tomato plants in Russia. Plants showing signs of PSTVd infection were found in greenhouses in Khabarovsk Region and Stavropol Region. Three isolates of viroids, H41, K168 and K169, were isolated. Phylogenetic analysis established their close relationship with the isolates infecting potato plants previously characterized in Russia. The analysis of the secondary structures of the detected isolates also showed their similarity to the previously characterized isolates. However, for the H41 isolate, the insertion of two nucleotides in the PM1 loop of the pathogenic VM region (VMR) was noted. Insertions in the PM1 loop increased the free energy values of this structural element. The information obtained suggests that genetically Russian isolates do not undergo significant changes in the main structural elements even during the transition from potato to tomato, but there are insertions in the PM1 loop related to the virulence modulation region.