A disease showing chlorosis, leaf rolling and stunting in Vicia faba and other legumes was observed in West Asia and North Africa during 1987-1988. The putative causal agent could not be transmitted mechanically, but could be transmitted by aphids, most efficiently by Acyrthosiphon pisum, in the persistent manner. Further studies revealed isometric virus-like particles (VLPs) closely associated with the disease, although their infectivity could not be demonstrated by membrane feeding. These particles, measuring c. 18 nm in diameter and containing a capsid protein of about 22 kDa and ssDNA of about 1 kb, are hereafter designated faba bean necrotic yellows virus (FBNYV). A high proportion of circular nucleic acid molecules of about 0.9 kb were visualised by electron microscopy. Hybridisation analysis of cloned viral DNA suggests that the circular genome is larger than 1 kb and consists of several components of similar size. An antiserum produced against FBNYV was used in ELISA, immunoelectron microscopy (IEM) and Western blot experiments for virus detection in aphids and field samples and for serological comparison with other viruses. Weak heterologous reactions between FBNYV and subterranean clover stunt virus (SCSV) were detected in IEM, but could not be confirmed in ELISA or Western blots. No serological relationship to banana bunchy top virus (BBTV) was detected. Using a direct tissue blot immunoassay (TBIA), FBNYV was detected in vascular tissue of infected faba bean leaves and stems.

Early in 1999 a new viral disease occurred in protected tomato (Lycopersicon esculentum) crops in the Netherlands. Infected plants showed yellow leaf spots and mosaic. Transmission electron microscopic analysis revealed particles typical of potexviruses. Only three potexviruses have been reported to infect solanaceous crops: Pepino mosaic virus (PepMV), Potato aucuba mosaic virus (PAMV), and Potato virus X (PVX). Inoculation of test plants and serological tests showed that the new virus clearly differed from PAMV and PVX. Immuno-electron microscopy with antiserum to PepMV (1), the original PepMV isolate, and the virus from tomato showed decoration titers of 1:800 (homologous) and 1:400, respectively. Neither virus reacted with antiserum to PVX, nor did PVX react with antiserum to PepMV. Results of host plant analysis with 17 plant species mostly resembled those expected for PepMV. Nucleotide sequence alignment of DNA fragments obtained by reverse-transcriptase polymerase chain reaction with a specific primer set for potexviruses, directed against the RNA polymerase region, showed 93% identity between PepMV and the virus from tomato, while homologies with PVX, PAMV, and other potexviruses were <60%. Results indicate that the potexvirus in tomato is PepMV. PepMV was first found in pepino (Solanum muricatum) in Peru in 1974 and described by Jones et al. in 1980 (1). This is the first report of a natural infection of tomato by PepMV. Reference: (1) R. Jones et al. Ann. Appl. Biol. 94:61, 1980.

Antisera to the bacterially expressed nonstructural proteins (NSP) HC-Pro, CI, NIa, and NIb and the coat protein (CP) of plum pox potyvirus (PPV) were used for analysing the composition of virus-induced cytoplasmic and nuclear inclusions by electron microscopy. The antisera reacted with NSP and CP of PPV on immunogold-labelled ultrathin sections. Antiserum to CP reacted with virions of seven out of 18 other potyviruses. CP was distributed throughout the cytoplasm of infected cells. Antisera to PPV NSP specifically reacted with virus-specific cytoplasmic and/or nuclear inclusions induced by 17 different potyviruses. NSP were furthermore localized in confined cytoplasmic areas in between complex accumulations of virus-specific inclusions. Cylindrical inclusions induced by the potyviruses were proven to consist of CI protein. Most other cytoplasmic or nuclear inclusions were shown to be composed of two or more NSP. An unexpected composition of virus-induced inclusions was observed for the crystalline nuclear inclusions of tobacco etch virus. Here, in addition to the expected presence of NIa and NIb, HC-Pro could be demonstrated. Furthermore, amorphous cytoplasmic inclusions induced by papaya ringspot virus contained the expected HC-Pro but additionally NIa, NIb and CI. Beet mosaic virus-induced nuclear inclusions ('satellite bodies') contained in their electron-dense matrix NIa, NIb, Hc-Pro and CI and in their lacunae CP in bundles of virion-like filaments. The results indicate that all cytoplasmic or nuclear inclusions of potyviruses have to be regarded as deposition sites of excessively produced viral NSP.

From naturally infected barley plants two types of barley yellow mosaic viruses have been isolated in Federal Republic of Germany. Both are identical in morphology, showing a bimodal length distribution (270–289 nm and 568–600 nm), and in symptomatology. Both induce conspicuous cytoplasmic inclusions of the pinwheel type and laminated aggregates, as well as threedimensional crystal‐like arrays of membrane material. The types differ, however, in buoyant density, serology, and transmissibility. One is transmissible by soil as well as mechanically (BaYMV‐M), and does not react with a Japanese antiserum to the Japanese virus (BaYMV‐J). The other type (BaYMV‐NM) is only transmissible by soil and reacts with BaYMV‐J‐antiserum. From mechanically infected plants BaYMV‐M was purified, and an antiserum was produced, from soil‐infected plants only mixtured BaYMV‐NM and ‐M could be obtained. BaYMV‐NM prevailed during winter, but with rising temperatures in spring BaYMV‐M was predominant. BaYMV‐M and the ‐M‐NM mixture had each two species of nucleic acids (2.7–2.8 × 106 and 1.4–1.5 × 106 d) and two major protein subunit bands were found in SDS‐PAGE (35–36 × 103 and c. 29 × 103 d).

A full-length cDNA clone of an aphid non-transmissible isolate of plum pox potyvirus (PPV) was rendered biologically active when placed under the control of the cauliflower mosaic virus 35S RNA promoter and the nopaline synthase polyadenylation signal. The cDNA was constructed so that the exact 5' end of the PPV RNA was present at the transcription initiation site.Inoculation of plasmid DNA onto Nicotiana benthamiana led to systemic infection, whereas local lesions were produced in Chenopodium amaranticolor and C.quinoa, typical of an infection with PPV. Examination of infected plants revealed PPV-specific virus particles as well as viral RNA, the coat protein and the nonstructural large nuclear inclusion protein (NIb).Potyviruses belong to the largest group of plant viruses and cause serious diseases in a number of economically important crop plants. Members of the potyvirus group are flexuous rods 720 to 900 nm in length (Hollings & Brunt, 1981) and encapsidate a single positive-sense RNA molecule of about 10 kb, attached to a 5'-linked protein (VPg) and including a poly(A) tract at the 3' end. The RNA is translated into a large polyprotein which is subsequently processed by at least two virus-encoded proteases. Upon proteolytic cleavage this polyprotein yields the viral coat protein (CP) and the non-structural proteins helper component-protease, cylindrical inclusion protein and two nuclear inclusion proteins (NIa and NIb). In addition, at least two other gene products which have not yet been identified are predicted from the nucleotide sequence of all potyviruses sequenced (Allison et al., 1986;Balint et al., 1990;Domier et al., 1986;Lain et al., 1989;Maiss et al., 1989;Robaglia et al., 1989).The in vitro synthesis of biologically active RNAs from full-length cDNA clones has been reported for two potyviruses (Domier et al., 1989;Riechmann et al., 1990). Genetic manipulation of full-length cDNA together with the subsequent transcription of infectious RNA provide a powerful tool for the examination of the molecular biology of RNA viruses. Moreover, it has been shown that infectious RNA can be transcribed in vivo by unknown promoters from plasmids containing cDNA copies of RNA 3 of alfalfa mosaic virus (Dore & Pinck, 1988), tobacco necrosis satellite RNA (van Emmelo et al., 1987) and potato spindle tuber viroid (Crees et al., 1983). Recently, Mori et al. (1991) have described the infectivity of plasmids containing the 35S RNA promoter of cauliflower mosaic virus (CaMV) upstream of fulllength cDNAs of all three brome mosaic virus (BMV) RNAs. Also, Commandeur et al. (1991) have demonstrated the infectivity of clones containing the 35S RNA promoter and cDNAs of RNA 3 and RNA 4 of beet necrotic yellow vein virus when complemented with a virus isolate which contains only RNA 1 and RNA 2. In this paper, the construction of a plasmid containing a full-length cDNA of an aphid non-transmissible isolate of plum pox potyvirus (PPV-NAT;Maiss et al., 1989) linked to the 35S RNA promoter of CaMV is described. PPV host plan...