Epidemiological evidence that vegetatively propagated, solanaceous plant species act as sources of Potato spindle tuber viroid inoculum for tomato

In autumn 2006 in the Netherlands, Potato spindle tuber viroid (PSTVd) infections were detected in 42·3 and 71·9% of professionally grown lots of Brugmansia spp. and Solanum jasminoides respectively. The infected lots contained 73 985 and 431 374 plants, respectively, demonstrating the presence of many potential viroid sources for tomato ( Solanum lycopersicum ). PSTVd was identified in cultivars of Brugmansia × candida , B. × flava , B. sanguinea , B. suaveolens and unspecified Brugmansia species/cultivars. Most infected lots of Brugmansia spp. originated from a single Dutch nursery; most infected lots of S. jasminoides originated abroad. Sequence analysis revealed that the PSTVd genomes from Brugmansia spp. contained an average of 360 nt, whereas all genomes from S. jasminoides except one consisted of 357 nt. Furthermore, the collective PSTVd genotypes showed polymorphism at four or more positions, except for two cases in which genotypes from Brugmansia spp. and S. jasminoides were identical. Phylogenetic studies showed that PSTVd genotypes from Brugmansia spp. and S. jasminoides grouped apart from each other and from PSTVd isolates from potato ( Solanum tuberosum ) and Physalis peruviana . The PSTVd genotypes from tomato did not form a separate cluster, but were dispersed over clusters of vegetatively or partly vegetatively propagated plant species, i.e. potato, P. peruviana and S. jasminoides . Moreover, mechanical inoculation of the predominant PSTVd genotypes from S. jasminoides to tomato was successful. These results provide evidence that vegetatively propagated, solanaceous plant species have been sources of infection for tomato crops in the past.