Guido Boccardo

Cryptic plant viruses.

Publisher Summary It is interesting that at this relatively late stage in virus research, new kinds of viruses continue to come to light. Cryptic viruses successfully evaded detection until recently because they induce no or, perhaps in some cases, very slight disease symptoms, are not transmissible in the ordinary way, and have particles present in such low concentrations as to escape casual discovery. The fact that cryptic viruses appear to cause no economically important disease has tended to give them low research priority. Nevertheless they are of interest as they contain double-stranded (ds) RNA, present only in another very different group of plant viruses, and appear unable to pass from carrier to non-carrier cells across a graft union. The latter is a decidedly non-virus like property. They are also of practical importance as they may be responsible for misleading results with methods for the detection of single-stranded RNA viruses based on the presence in plants of the double-stranded replicative forms.

Electrophoretic separation of dsRNA genome segments from Fiji disease and maize rough dwarf viruses

By employing two different buffer solutions for polyacrylamide gel electrophoresis, all genome segments of Fiji disease and maize rough dwarf virus were separated. Fiji disease virus contains ten genome segments with approximate genome molecular weights of 19.26 x 10(6) and 19.85 x 10(6), depending on the buffer employed for electrophoresis. Maize rough dwarf virus possesses ten dsRNA segments and according to the buffer employed for electrophoresis the approximate molecular weights of the genome were 18.91 x 10(6) and 19.61 x 10(6). In the samples of maize rough dwarf virus analysed, the evidence indicates that two types of virions were present which were distinguished by a slight difference in molecular weight for segment 10. The electrophoretic patterns for all dsRNA components of Fiji disease and maize rough dwarf viruses were very similar suggesting a close relationship between them.

A Geminivirus, Serologically Related to Maize Streak Virus, from Digitaria sanguinalis from Vanuatu

SUMMARY Electron microscopy of purified particles of a virus found in Dig#aria sanguinalis from Vanuatu (formerly New Hebrides) indicated that it is a geminivirus. Preparations of virus particles contained one coat protein of tool. wt. about 27 500 and circular and linear single-stranded DNA about 2350 nucleotides in length. In thin sections of infected cells, geminate particles were found in crystalline arrays both in nuclei and in the cytoplasm. The virus is serologically related to maize streak virus but differs from it with a serological differentiation index of 3.

Three seedborne cryptic viruses containing double-stranded RNA isolated from white clover

White clover cryptic viruses (WCCV) 1, 2, and 3 were purified from apparently healthy plants with yields of about 200 mug of virus/kg of tissue. After isopycnic centrifugation in CsCl, WCCV 1 and 2 formed homogeneous bands at densities of 1.392 and 1.375 g/ml, respectively, whereas WCCV 3 was not recovered. Particles of WCCV 1 and 3 were 34 nm in diameter, without obvious morphological subunits, whereas WCCV 2 particles were 38 nm in diameter, with prominent morphological subunits. Antisera with titers up to 1:2048 were obtained against WCCV 1 and 2. Each of the three viruses contained two segments of linear dsRNA (Mr from 1.03 to 1.49 X 10(-6). Virus-like particles, probably those of WCCV 1 and 2 were detected in low numbers in the cytoplasm of about 1/10 of the parenchyma cells of carrier plants examined by thin sectioning. The particles of WCCV 1 and 2 were not transmitted by grafting or mechanical inoculation, but were seed transmitted. Evidence is given that WCCV 1 and 2 multiply in their carrier plants, and are not viruses of associated parasitic or commensal organisms.

The maize rough dwarf virion. I. Protein composition and distribution of RNA in different viral fractions.

Abstract The protein composition and RNA content of maize rough dwarf virus virions, spiked cores and smooth cores were examined by polyacrylamide-gel electrophoresis. All fractions contained the whole spectrum of dsRNAs except spiked cores produced by heating. The virion contained six polypeptides numbered, respectively, from I to VI, with molecular weights of 139,000, 126,000, 123,000, 111,000, 97,000 and 64,000. The spiked core contained peptides I–III and the smooth core probably contained only peptides I and II. Consequently the B spikes should be composed of peptide III. Peptides IV–VI are part of the outer capsid.

The maize rough dwarf virion: II. Serological analysis

Abstract A serological analysis was made on maize rough dwarf virus fractions by immune electron microscopy, gel diffusion and slide precipitin tests to investigate the reactions of both protein and RNA. Antisera were made against different virus fractions, and existing sera against rice black streaked dwarf and maize rough dwarf viruses were also tested. Some of the sera contained antibodies against viral dsRNA. The serological behavior of poly[I]:poly[C] was similar to but not identical with that of viral RNA. One antigenic group in smooth cores was identified, and an additional group was found in spiked cores, associated with B spikes. Attempts to obtain antibodies against the outer capsid were not successful. A soluble antigen was identified as viral RNA. Disrupted protein preparations containing sodium dodecyl sulfate reacted with normal sera as well as virus antisera.

Relationships between the Cryptic and Temperate Viruses of Alfalfa, Beet and White Clover

Small isometric virus particles containing double-stranded RNA have been independently reported in Europe and Japan from apparently healthy alfalfa (Medicago sativa), beet (Beta vulgaris), and white clover (Trifolium repens). They have been called cryptic viruses in Europe and temperate viruses in Japan. Serological comparison using immunoelectron microscopy, and polyacrylamide gel electrophoresis of the RNAs indicate that alfalfa cryptic and temperate viruses are the same, beet cryptic virus is probably a mixture of two different viruses, one of which is similar to or the same as beet temperate virus, and white clover temperate virus is a mixture of at least three different viruses, two of them indistinguishable from white clover cryptic viruses 1 and 2, respectively, and the third very likely the same as white clover cryptic virus 3.

The Coat Proteins and Nucleic Acids of Two Beet Cryptic Viruses

Summary Purified particles of beet cryptic virus (BCV) contained two protein species with estimated mol. wt. of 5.45 × 104 and 5.25 × 104, and four nucleic acid species of mol. wt. 1.36, 1.15, 0.94 and 0.87, all × 106. These nucleic acids were shown to be dsRNA on the basis of thermal denaturation profile, isopycnic sedimentation in Cs2SO4 solutions, electron microscopical appearance and nuclease resistance. Previous work has shown that a cryptic virus from leaf beet in Japan reacts with BCV antiserum but contains only two dsRNA species that co-migrate with the two larger RNAs of BCV. These and our results suggest that BCV is a mixture of two viruses, although this was not evident from the appearance of the particles in the electron microscope.

DNA-based methods for the detection and the identification of phytoplasmas in insect vector extracts.

DNA extraction and storage methods have been evaluated with laboratory-reared leafhoppers and/or field-collected leafhoppers and psyllids. Detection of four different phytopathogenic phytoplasmas, belonging to three taxonomic groups, has been achieved by several direct or nested polymerase chain reaction (PCR) methods with such DNA extracts. Reactions differed in both the 16/23S ribosomal primer pairs used and the specific assay and cycling conditions. Merits and possible hindrances of the various primer pairs, in relation to insect DNA extracts, are discussed. However, identification of the phytoplasma(s) necessarily relied on comparison of the polymorphism in length of the amplified DNA fragments obtained by restriction with appropriate endonucleases. Endonuclease digestion is crucial for determining the identity (subgroup affiliation) of phytoplasmas of the same groups that can be carried by an individual vector.

Morphology and Nucleic Acid of Rice Gall Dwarf Virus

In negative stain preparations, the particles of rice gall dwarf virus (RGDV) had the form of angular icosahedra, approximately 65 nm in diameter, and resembled Phytoreovirus particles. The genomic double-stranded RNA of RGDV was fractionated by PAGE into 12 segments similar to those of the RNAs of the phytoreoviruses, wound tumor virus and rice dwarf virus, but of different mobilities. The RNAs were distinct from those of other plant reoviruses. RGDV therefore is confirmed as a new Phytoreovirus.