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The complete nucleotide sequence of a Beijing isolate of Wisteria vein mosaic virus was determined to be 9695 nucleotides in length excluding the poly(A) tail. Sequence analysis predicted a single large open reading frame of 9279 nucleotides potentially encodes a polyprotein of 3092 amino acids. Phylogenetic analysis based on the genomic and deduced amino acid sequences support the current status of Wisteria vein mosaic virus (WVMV) as a distinct virus of the genus Potyvirus and a member of the Bean common mosaic virus (BCMV) subgroup. Sequence comparisons of WVMV and other members of the BCMV subgroup showed that WVMV is most closely related to both soybean mosaic virus and watermelon mosaic virus. [ABSTRACT FROM AUTHOR]

Euonymus bungeanus plants exhibiting symptoms of abnormal branches, small leaves and phyllody, which is indicative of E. bungeanus witches' broom (Eb WB) disease, have recently been found in Beijing, China. A phytoplasma from symptomatic E. bungeanus plants was identified by 16S rRNA polymerase chain reaction ( PCR) using the phytoplasma-specific universal primer pair R16mF2/R16mR1. Inoculation of healthy E. bungeanus plants by grafting with diseased scions was also performed. The rp and secY genes of the Eb WB phytoplasma were cloned and sequenced as was the 16S rRNA gene. Sequence and phylogenetic analyses of 16S rRNA, rp and secY genes indicated that the phytoplasma associated with E. bungeanus belongs to the 16SrV-B, rpV-C and secY-C subgroup, the same subgroup as the jujube witches' broom ( JWB) phytoplasma that is widely distributed among jujube trees in China. Comparative analyses based on virtual restriction fragment length polymorphism ( RFLP) showed that the Eb WB phytoplasma is more closely related to another 16SrV-B subgroup strain: RPWB ( Robinia pseudoacacia witches' broom). To the best of our knowledge, this is the first report of a witches' broom phytoplasma in E. bungeanus in China, and the findings add a new cultivated plant species to the already broad natural host range of 16SrV-B subgroup phytoplasmas. [ABSTRACT FROM AUTHOR]

Acidovorax citrulli causes seedling blight and bacterial fruit blotch ( BFB) of cucurbits, a serious disease threat to cucurbit seed and fruit production worldwide. Despite its economic importance, current knowledge on the biology and pathology of A. citrulli is limited. This work studies a mini-Tn 5 mutant, MJ22-3, that showed reduced virulence on melon seedlings. The gene disrupted by Tn 5 was identified as leuB, which encodes a putative 3-isopropylmalate dehydrogenase, an enzyme that appears to be essential for leucine biosynthesis. The leuB gene in-frame deletion mutant MΔleuB, as well as the Tn 5-inserted mutant MJ22-3, failed to grow in minimal medium without leucine and exhibited reduced swimming motility; however, the mutations had no effect on biofilm formation or induction of the hypersensitive response on tobacco ( Nicotiana tabacum). When inoculated at a low cell density (104 CFU mL−1), the leuB gene mutants showed a significantly slower growth rate and attenuated virulence on melon cotyledons compared to the wildtype MH21. However, inoculations with the mutants at high concentration (108 CFU mL−1), or low concentration (104 CFU mL−1) inoculations supplemented with 0·01% leucine resulted in growth rates and disease severities similar to that of the wildtype MH21. The results suggest that leucine biosynthesis is essential for both in vivo growth and full virulence of A. citrulli MH21 on melon seedlings. [ABSTRACT FROM AUTHOR]

Chinese chestnut trees ( Castanea mollissima BL.) planted in a suburb of Beijing, China developed symptoms including yellowing, leaf crinkling, little leaf, shortened internodes, and empty burrs. Transmission electron microscopy revealed presence of phytoplasma cells in phloem sieve elements of the symptomatic chestnut trees. Molecular cloning and sequence analysis of PCR-amplified near-full length 16S rRNA gene indicated that the phytoplasma associated with the Chinese chestnut yellow crinkle disease is closely related to Japanese chestnut witches'-broom phytoplasma. This is the first report of a phytoplasmal disease in Chinese chestnut trees. [ABSTRACT FROM AUTHOR]

This study determined the tuf gene sequence of the phytoplasma specific to paulownia witches’-broom from Nanyang, China (hereby designated PaWB-Ny). The PaWB-Ny tuf gene was 1185 nucleotides in length and confirmed that the phytoplasma belongs to subgroup 16SrI-D of aster yellows. Three characteristic GTP-binding protein motifs were identified based on the peptide deduced from the tuf gene sequence. Results suggested that the elongation factor EF-Tu was localized in the cytoplasm and lacked hydrophobic transmembrane domains. Antibodies against PaWB-Ny EF-Tu were prepared by rabbit immunization with glutathione-S-transferase (GST)-tagged EF-Tu fusion protein expressed in Escherichia coli. EF-Tu exhibited a molecular weight of ∼43 kDa and was detected in PaWB-infected paulownia plants by western blot analysis. Indirect enzyme-linked immunosorbent assays (ELISA) and dot blotting analyses were performed with freezing and thawing treatments during antigen preparation. Dilution of extracts to an appropriate scale significantly reduced non-specific reactions. The resultant PaWB EF-Tu antibody reacted with antigens from plants infected with periwinkle virescence and chinaberry tree witches’-broom phytoplasmas, but not those infected with jujube witches’-broom or bishopwood witches’-broom phytoplasma. The EF-Tu was characteristically localized within the phytoplasmal cytoplasm of infected plant phloem tissues. [ABSTRACT FROM AUTHOR]

Wisteria mosaic is a common disease of Wisteria spp. in many regions of China. According to a recent survey, the incidence of this disease was about 40% on ornamental wisteria in gardens and courtyards in the Beijing area, China. In the most severely affected areas, about 80% disease incidence was recorded. In 2002, mosaic symptoms on W. sinensis were found on the west campus of China Agricultural University in Beijing. The symptoms included flecking, yellowing, vein clearing, mottling or mosaic on the leaves; similar to those of wisteria mosaic disease reported in other countries.