No abstract

No abstract

Psorosis, sometimes also associated with ringspot symptoms, is a widespread and damaging disease of citrus in many parts of the world including South America and the Mediterranean basin. We describe the application of RT‐PCR and DAS‐ELISA diagnostics to an isolate of citrus ringspot virus (CtRSV‐4) and other virus isolates associated with this disease. Fragments of cDNA from bottom‐component RNA of CtRSV‐4 were cloned and sequenced, and PCR primers were designed, 5′ACAATAAGCAAGACAAC upstream, and 5′CCATGTCACTTCTATTC downstream. RT‐PCR experiments using these primers allowed detection of CtRSV‐4 in infected citrus leaves down to a tissue dilution of 1/12 800 representing 2 μg of tissue, and less sensitive detection of the related citrus psorosis‐associated virus (CPsAV90‐1‐1) and four other psorosis isolates from Argentina and the USA. In addition, CtRSV‐4 particles were partially purified from local lesions in Chenopodium quinoa, and the preparations used to raise a rabbit antiserum. The antiserum was absorbed with extracts of healthy C. quinoa leaves, and a DAS‐ELISA kit was prepared and tested for detection of CtRSV‐4, CPsAV90–1‐1, and other psorosis isolates from Argentina, the USA, Italy and Spain. The ELISA detected CtRSV‐4 down to a tissue dilution of 1/1600, and most other psorosis isolates down to dilutions of 1/200–1/800. Three of a total of 20 heterologous isolates were consistently negative. Comparison of the PCR and ELISA results suggests that both methods can be used for detection of a range of psorosis isolates, but that variation of the viruses in the field might cause problems for any one diagnostic test.

No abstract

No abstract

An undescribed virus, here named ranunculus white mottle virus, was isolated in Italy from cultivated ranunculus showing mottle and distortion of leaves. The virus was mechanically transmissible to several herbaceous hosts. In negative stain, the particles appeared as circularised supercoiled threads 3 nm in diameter of different contour lengths; in some conditions the circles collapsed to form linear pseudobranched structures 9 nm in diameter. Immunolabeling of thin sections showed that viral antigen was widely distributed in the cytoplasm of parenchyma cells. The virus was not serologically related to the morphologically similar tenuiviruses, citrus psorosis-ringspot virus and tulip mild mottle mosaic virus. A major 43 kDa protein was present in purified preparations and in infected plant tissue, as also was a minor 28 kDa protein, serologically related to the major one. Nucleic acids extracted from purified particles consisted of at least three RNAs, of approximately 7.5, 1.8 and 1.5 kb, which appeared partly in single- and partly in double-stranded form. Purified preparations, but not viral RNAs, when mechanically inoculated, were infectious. Host range, tissue tropism, particle morphology and coat protein size place the virus closest to citrus psorosis-ringspot and tulip mild mottle mosaic viruses. These three viruses in turn show similarities with the Tenuiviruses and Bunyaviridae.

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 (i) alfalfa cryptic and temperate viruses are the same, (ii) 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 (iii) 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.

Tospovirus serogroups I and III have recently been designated as species, tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV), while the species status of serogroup II isolates remains undefined. Fifteen Tospovirus isolates from ornamental and vegetable crops in Liguria, Italy, were found to belong either to TSWV (seven isolates) or to INSV (eight isolates) on the basis of test‐plant reactions, serological techniques using DAS ELISA kits raised against the nucleoproteins of the type members of the two species, and cytopathology. None of them could be assigned to serogroup II using DAS ELISA kits raised against nucleoproteins of this serogroup. Italian isolates representative of the two species reacted in indirect ELISA using a polyclonal antiserum against the entire particle of a TSWV isolate, but with higher intensity for our TSWV isolates than for the INSV isolates. Western blots and dot immunobinding assays confirmed that the nucleoproteins of the two species are unrelated whereas the glycoproteins are related. The cytopathology was similar for two isolates representative of TSWV and INSV, except that the type of filaments encountered was different, and appeared to be characteristic of the species.