A bacilliform virus from Dioscorea alata, designated Dioscorea alata bacilliform virus (DaBV), from Barbados and West Africa and from other Dioscorea spp. from West African, Carribean, Asian and South American countries, has been characterized. The virus was transmitted by the mealybug, Planococcus citri and by mechanical transmission of partially purified preparations to several Dioscorea spp. DaBV was serologically related to a distinct bacilliform virus from Dioscorea bulbifera, to one isolate of sugarcane bacilliform badnavirus and two isolates of banana streak badnavirus (BSV) but was not related to another isolate of BSV or to Kalanchoe top spotting or cacao swollen shoot badnaviruses. The coat protein of DaBV was about 56 kDa and the nucleic acid was double‐stranded DNA of about 7.5 kbp, part of which showed distant homology with other badnaviruses. Thus, DaBV is a distinct hitherto uncharacterized badnavirus.
Cowpea mild mottle virus (CMMV) has physicochemical properties typical of carlaviruses, but has remained unclassified due to a number of unusual properties, including no serological cross-reaction with l 8 carlaviruses; production of brush-like inclusion bodies in vivo; and the ability to be transmitted by whiteflies (Bermisia tabaci).In this paper we report the use of a carlavirus specific PCR primer to identify CMMV as a member of the carlavirus group. This is confirmed by nucleotide sequence (958 nucleotides) from the 3' terminal region of CMMV RNA which contains a partial open reading frame (ORF) having high similarity with the coat proteins of other carlaviruses. The sequence also contains an 11.7K ORF at the 3' terminus, containing a 'zinc-finger' motif which is unique to carlaviruses.Cowpea mild mottle virus (CMMV) has physicochemical properties which resemble those of members of the carlavirus group, namely the presence of filamentous particles c. 650 nm in length, consisting of a coat protein of 31-33K and a single-stranded RNA of Mr 2.5 x 10 6 [Jeyanandarajah and Brunt, 1993]. However, unlike other members of the carlavirus group which are transmitted non-persistently by aphids [Foster, 1992], CMMV is unusual in that it is transmitted in a non-persistent manner by whiteflies (Bemisia tabaci) [Jeyanandarajah and Brunt 1993]. In addition, CMMV has several other unusual properties compared with other carlaviruses, which include, no serological relationships with 18 recognised members of the carlavirus group, and the induction of unusual brush-like intracellular inclusions in infected plants [Brunt et al., 1983]. It has been suggested that CMMV remain unclassified until the taxonomic significance of these differences have been investigated further [Jeyanandarajah and Brunt, 1993].We report here attempts to develop a rapid and specific identification test for carlaviruses which can also be used to determine whether CMMV and similar unclassified viruses are species of the carlavirus genus. The test is based on the polymerase chain reaction (PCR) using primers to conserved and unique sequences in carlavirus RNAs.The overall genome organisation of carlaviruses is very similar to that of potexviruses with the virus genes of both genera being arranged (from 5' to 3') as replicase, a triple gene block (25K, 12K, and 7K), and coat protein open reading frame, with extensive similarity at the amino acid level between the equivalent proteins of potex-and carlaviruses. However, in addition to these proteins, carlavirus genomes contain an additional protein encoded by an open reading frame
Phytopathology 69, 441-445. 13-24.
SUMMARY Ullucus virus C (UVC) is a comovirus prevalent in Ullucus tuberosus grown at high altitudes in the Bolivian and Peruvian Andes. It was transmitted mechanically to U. tuberosus (Basellaceae) and to five of 26 species from three of eight other families, infecting U. tuberosus symptomlessly but inducing conspicuous systemic infection in Chenopodium amaranticolor and C. quinoa. Sap from infected C. quinoa was usually infective after 10 min at 70 but not 75 °C, after dilution to 10‐7 but not 10‐8, and after 8 but not 16 wk at 20 °C. UVC was not transmitted by either of two aphid species (Aphis gossypii and Myzus persicae) or through seed of C. quinoa, but it was transmitted by leaf contact between infected and healthy plants. UVC has isometric particles which, in neutral phosphotungstate, are c. 28 nm in diameter. The particles sediment as three components (T, M and B) with sedimentation coefficients (s˚20, w) of 51 S (T), 95 S (M) and 116 S (B). M component particles have a buoyant density (g cm‐3) in caesium chloride of 1.404, and B component particles separated into minor and major sub‐components with densities of 1.409 and 1.463, respectively. T, M and B particles were serologically indistinguishable, and each contained similar relative amounts of two polypeptides of mol. wts 20 700 and 45 100. T particles contained only protein, but M particles also contained c. 30% ss‐RNA of mol. wt 1–45 ×106 and B particles c. 38% ss‐RNA of mol. wt 2·2 × 106. The virus is serologically distantly related to cowpea mosaic virus but, as it showed no relationship to any of 11 other similar viruses, it is probably a distinct member of the comovirus group.
SUMMARY Hibiscus latent ringspot virus (HLRV) was prevalent in Hibiscus rosa‐sinensis in Ibadan, Nigeria. It was readily transmitted mechanically to 22 of 73 species from seven of 20 families, but was best propagated in Nicotiana clevelandii or Hibiscus cannabinus and assayed in Chenopodium murale. HLRV was readily purified from systemically infected hosts by differential centrifugation of leaf extracts clarified with 8.0% n‐butanol, followed by molecular permeation chromatography on controlled‐pore glass beads (700 Å, 120–200 mesh). The virus has isometric particles c. 28 nm in diameter which sedimented as three components (T, M and B), with sedimentation coefficients (s°20, w) of 51; 114 and 132 S and buoyant densities in caesium chloride of 1.32, 1.49 and 1.52 g/cm3, respectively. All three components contained a single polypeptide of rnol. wt 53.6 × 103. T component particles contained only protein but M and B components also contained single‐stranded RNA of rnol. wt 2.2 × 106 and 2.5 × 106, respectively. The properties of HLRV suggest affinities with nepoviruses but no serological relationship was detected between HLRV and 15 recognised or possible members of the nepovirus group.
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