In 2008, in the framework of surveying for pospiviroids, nine symptomless clones of Celosia plumosa (Voss) Burv. (Amaranthaceae) from a Dutch breeding company were tested by reverse transcription (RT)-PCR with primer sets Pospi1-RE/FW and Vid-RE/FW (4). In four samples, amplicons of 227 nt were obtained with primers Pospi1-RE/FW. Sequencing of the amplicons showed identities of more than 99% to the partial sequence of Iresine viroid 1 (IrVd-1) from Alternanthera sessilis, NCBI GenBank Accession No DQ846886 (2). Subsequently, a set of primers was designed to amplify the complete viroid genome, i.e., IrVd-FW1 5′-GCG GAA GAA ACA GGA GCT CGW CT-3′ and IrVd-RE1 5′-CGC GWG GAG TTC TCC GGT CTT TA-3′ -- identical to nt 168 to 190 and 145 to 167 of the complete IrVd-1 sequences in the NCBI GenBank (Nos. DQ094293, DQ094294, NC_003613, and X95734). One isolate from C. plumosa was amplified with this primer pair and amplicons were cloned into the pGEM-T Easy Vector System II. Sequencing of one individual cDNA clone (GenBank Accession No. GU911350) revealed a genome size of 370 nt and 98.1% sequence identity to the IrVd--1 isolate from Vinca major, GenBank Accession No. DQ094293 (1). Hence, the viroid was identified as IrVd-1. The isolate from C. plumosa was also mechanically inoculated to 10 healthy plants of C. plumosa, chrysanthemum (Chrysanthemum × morifolium) cv. White Delianne, potato (Solanum tuberosum) cv. Nicola, and tomato (Solanum lycopersicum) cv. Moneymaker. No symptoms were observed over a 6-week period, and RT-PCR with primers Pospi1-RE/FW on bulked samples of five plants per species only identified IrVd-1 in both samples of C. plumosa. For tomato, these results confirm those of Spieker (3). Therefore, in contrast to the other pospiviroids, it seems unlikely that IrVd-1 poses a threat to potato and tomato.
References: (1) X. Nie et al. Can. J. Plant Pathol. 27:592, 2005. (2) R. P. Singh et al. Plant Dis. 90:1457, 2006. (3) R. L. Spieker. J. Gen. Virol. 77:2631, 1996. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.
