Black locust tree-a potentially important reservoir host of sophora yellow stunt virus in Iran

Black locust (Robinia pseudoacacia L., Fabaceae) is a shade tree and commonly used in urban green spaces in Iran. In the current study, 13 symptomatic black locust samples showing withering and decline were collected within the campus of Shahid Bahonar University of Kerman (southeastern Iran) and sophora yellow stunt virus (SYSV, genus Nanovirus, family Nanoviridae) was detected in two samples using nanovirus degenerate primers by PCR assay and sequencing of amplicons. Subsequently, eight genome components of the Rob4 isolate were amplified using specific primer pairs and sequenced. Sequence analysis showed that the Rob4 isolate shared 93.3-99.8% nucleotide identity with the previously sequenced genome of isolate Ta1 from a plant of Sophora alopecuroides also growing at the university campus and 68.9-99.8% nucleotide identity with the other sequences of SYSV available in GenBank. To demonstrate the pathogenesis of SYSV in black locust seedlings, previously constructed clones of the SYSV genome components were used for agroinoculation resulting in the appearance of severe symptoms followed by wilting and death of seedlings. Based on the results of this study, black locust tree is identified as a permanent reservoir host of SYSV in Iran. To the best of our knowledge, this is the first report of the infection of a nanovirus with a symptomatic perennial tree having woody trunk.