Helenium virus S

Abstract: A carlavirus was isolated from leaves of a dandelion plant raised in the experimental garden of the Hugo de Vries Laboratory in Amsterdam. The virus was readily sap-transmissible and infected 24 out of the 52 plant species and cultivars tested, with visible symptoms in 18 of them.Myzus persicae andCuscuta subinclusa (dodder) did not transmit the virus. In addition the virus was not seed-transmitted in dandelion. Dilution end-point was 10−5, thermal inactivation occurred at between 80–85°C and longevity in vitro was approximately 24h. The virus had a sedimentation coefficient of 136 S. Polyacrylamide gel electrophoresis of the coat protein gave two bands, consisting of proteins with molecular masses ranging from 37 000 to 34 300 Da (band I) and from 34 000 to 32 800 Da (band II). The molecular mass of the RNA was 2.84 x 106 Da. The average buoyant density of the virus was 1.306 gcm−3 and the average A260/A280 ratio 1.16. The virus particles had a normal length of 668 nm. with the light microscope, large mainly vacuolate inclusions were observed in the epidermal cells of infectedNicotiana cleavelandii leaves. In ultra-thin sections of systemically infected leaves ofN. clevelandii, bundles of aggregated virus particles were detected, whereas in infected dandelion leaves there were fewer aggregates and more scattered virus particles. There was a close serological relationship to dandelion latent virus, chrysanthemum virus B and potato virus S and a more distant one to carnation latent virus, elderberry carlavirus,Helenium virus S and potato virus M. The occurrence of the virus was found to be restricted to dandelion plants in the experimental garden in Amsterdam. On the basis of large differences in host range, symptomatology and lack of transmission byM. persicae it was decided that the virus could not be considered a strain of either dandelion latent virus, chrysanthemum virus B or potato virus S. We therefore propose that it be called dandelion carlavirus.

Abstract: Samples of commercially grown Impatiens holstii from several sources in Minnesota contained a carlavirus which serologically was closely related, if not identical with Helenium virus S described earlier in Germany. The two viruses have similar experimental host ranges and caused similar cytopathogenic effects. After mechanical transmission the Impatiens isolate produced less severe symptoms in Impatiens than the Helenium isolate. Only the latter isolate was transmitted by Myzus persicae in the non-persistent manner.

Abstract: The sequence of 380 nucleotides upstream of the start codon of the open reading frame (ORF) of the coat protein of the carlavirus Helenium virus (HelVS) was determined from cloned cDNA. This portion of the viral RNA contained one complete ORF encoding a protein of 7 K which had homology with similar sized proteins from other members of the carla- and potexvirus groups. Sequence data was also obtained beyond the start codon of the 7 K ORF into what was presumed to be the 12 K protein gene of the previously identified triple gene block of carla- and potexviruses. Significant sequence similarity of 46.3% and 41.6% was evident at the amino acid level with the equivalent regions of the 12 K proteins of potato virus S, Andean strain (PVSA) and potato virus M (PVM), respectively, with 25.4% similarity detected with the equivalent region of potato virus X (PVX).