The complete nucleotide sequence of isolates of Cucumber vein yellowing virus (CVYV) has been determined. The viral genome comprises 9734 nucleotides, excluding a 3'-terminal poly(A) sequence. The genome of CVYV has a 5'-non coding and a 3' non coding region of respectively 67 and 240 nucleotides. The RNA of CVYV encodes a single polyprotein of 3148 amino acid residues and has a deduced genome organization and motifs typical for a member of the family Potyviridae. However, CVYV is atypical because it lacks a coding sequence region for the putative helper-component as well as conserved helper-component-proteinase motifs which may account for its vector relations. All the present coding regions were compared to those from several members of the Potyviridae family. CVYV is most closely related to Sweetpotato mild mottle virus confirming its assignation to the genus Ipomovirus, despite similarities with tritimoviruses.

In the autumn of 2000, an outbreak of a disease caused considerable losses in greenhouse cucumber crops in Almeria (Spain). Infected plants showed vein clearing followed by chlorosis in leaves and yellow/green chlorotic spots on fruits. These symptoms as well as the presence of Bemisia tabaci in the crops suggested the possible involvement of Cucumber vein yellowing virus (CVYV), a proposed member of the Potiviridae family, which was first described in 1960 in Cucumis spp. from Israel (1). B. tabaci populations and leaves from cucumber plants were collected from the greenhouses and analyzed by RT-PCR using specific primers (CV(+): 5′-AGCTAGCGCGTATGGGGTGAC-3′; CV(-): 5′-GCGCCGCAAGTGCAA-ATAAAT-3′) that we designed based on the partial sequence published for CVYV (2). Total nucleic acid extracts from both B. tabaci individuals and the collected plants yielded amplification products of the expected size (449 bp), which were cloned and sequenced (Genebank accession number AJ301640). The sequence was 95.6% identical to that previously reported for CVYV. Nonviruliferous B. tabaci whiteflies were given a 24-h acquisition period on symptomatic leaves and then placed in groups of 15 insects on each of 10 healthy cucumber plants at the 4 leaf-stage for a 24-h inoculation period. Inoculated and control plants were analyzed 1 week later and the infection with CVYV was confirmed (10/10) by RT-PCR. Doublestranded RNA extractions from field-collected samples and from plants inoculated under controlled conditions suggested that no dsRNA formation was associated with the infection. This is the first report of CVYV in Spain. References: (1) S. Cohen and F. E. Nitzany. Phytopathol. Medit. 1:44, 1960. (2) H. Lecoq et al. J. Gen. Virol. 81:2289, 2000.

We describe the isolation and characterization of alfalfa-nodulating rhizobia from acid soils of different locations in Central Argentina and Uruguay. A collection of 465 isolates was assembled, and the rhizobia were characterized for acid tolerance. Growth tests revealed the existence of 15 acid-tolerant (AT) isolates which were able to grow at pH 5.0 and formed nodules in alfalfa with a low rate of nitrogen fixation. Analysis of those isolates, including partial sequencing of the genes encoding 16S rRNA and genomic PCR-fingerprinting with MBOREP1 and BOXC1 primers, demonstrated that the new isolates share a genetic background closely related to that of the previously reported Rhizobium sp. Or191 recovered from an acid soil in Oregon (B. D. Eardly, J. P. Young, and R. K. Selander, Appl. Environ. Microbiol. 58:1809–1815, 1992). Growth curves, melanin production, temperature tolerance, and megaplasmid profiles of the AT isolates were all coincident with these characteristics in strain Or191. In addition to the ability of all of these strains to nodulate alfalfa (Medicago sativa) inefficiently, the AT isolates also nodulated the common bean andLeucaena leucocephala, showing an extended host range for nodulation of legumes. In alfalfa, the time course of nodule formation by the AT isolate LPU 83 showed a continued nodulation restricted to the emerging secondary roots, which was probably related to the low rate of nitrogen fixation by the largely ineffective nodules. Results demonstrate the complexity of the rhizobial populations present in the acidic soils represented by a main group of N2-fixing rhizobia and a second group of ineffective and less-predominant isolates related to the AT strain Or191.

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