Publications

3567

A novel phytoplasma, designated strain SoyST1c1, associated with a newly emerging disease in soybean (Glycine max), known as soybean stunt (SoyST), was found in 2002 in a soybean plantation in Alajuela Province, Costa Rica. The same phytoplasma, or a very closely related strain, also infected sweet pepper (Capsicum annuum) with purple vein syndrome (SwPPV) and passion fruit vine (Passiflora edulis) with bud proliferation disease (PasFBP) in the same region. Sequence analysis of cloned 16S rRNA gene sequences (GenBank accession nos FJ226068–FJ226073 and HQ225624–HQ225635) indicated that all three affected plants were infected by phytoplasmas that shared <97.5 % sequence similarity with previously described phytoplasmas. The SoyST-causing phytoplasma represents a new taxon, most closely related to phytoplasma group 16SrI and 16SrXII strains. Virtual RFLP analysis indicated that the SoyST-causing phytoplasma and its closely related strains represent a novel 16Sr group, designated 16SrXXXI. Phylogenetic analysis of 16S rRNA gene sequences from the new phytoplasma strains, those previously described as ‘Candidatus Phytoplasma spp.’ and other distinct, as yet unnamed, phytoplasmas indicated that the SoyST-causing phytoplasma represents a distinct lineage within the aster yellows/stolbur branch on the phylogenetic tree. On the basis of its unique 16S rRNA gene sequence and biological properties, strain SoyST1c1 represents a novel taxon, for which the name ‘Candidatus Phytoplasma costaricanum’ is proposed with SoyST1c1 as the reference strain.

Winter oilseed rape (Brassica napus L.) is widely grown in Poland to produce vegetable oil for industrial processing of human and animal feed. In recent years, according to European Union directives on the use of biofuels (Directive 2003/30/EC), the area under oilseed rape cultivation in Poland has dramatically increased to 810,000 ha in 2009 and is still increasing. Morphological deformations of winter oilseed rape indicative of phytoplasma infection have been observed sporadically in Poland since 2000 (3). Plants exhibiting floral virescence, phyllody, as well as auxiliary bud proliferation, reduced leaves, and malformation of siliques were identified during surveys of research fields in Wielkopolska during May and June of 2009 and 2010. To confirm phytoplasma infection of these plants, inflorescence and leaf tissues were collected from nine diseased and three symptomless plants from three different field locations with 1 to 16% disease incidence. Total DNA was extracted from each plant tissue sample with a modified cetyltrimethylammoniumbromide method (2). Samples were analyzed for phytoplasma DNA with a nested PCR assay employing phytoplasma universal rRNA operon primer pair P1/P7 followed by R16F2n/R16R2, using previously described conditions (1). PCR products of 1.8 and 1.2 kb were obtained from all diseased plants only following PCRs with P1/P7 and nested primer pair R16F2n/R16R2, respectively. PCR products were not obtained from symptomless plants. Eight 1.2-kb amplicons were sequenced (GenBank Accession Nos. JN193475 to JN193482). Comparative analysis of the R16F2n/R16R2 rDNA sequences confirmed the phytoplasma origin of the rDNA sequences that shared 100 to 99% identity with Maize bushy stunt phytoplasma (GenBank Accession No. HQ530152), Alfalfa stunt phytoplasma (GenBank Accession No. GU289675), Primula green yellows phytoplasma (GenBank Accession No. HM590623), and other aster yellows group phytoplasmas. A 1.8-kb amplicon of isolate designated RzW14 was sequenced (GenBank Accession No. HM561990) and had 99% identity with Aster yellow group phytoplasmas from Lithuania (GenBank Accession Nos.GU223208 and AY744071). A virtual restriction fragment length polymorphism analysis of the 16S rDNA sequences from the R16F2n/R16R2 amplicons was performed with iPhyClassifier (4). Restriction profile comparisons identified all aster yellows group phytoplasmas as subgroup 16SrI-B strains. To our knowledge, this is the first report of a ‘Candidatus Phytoplasma asteris’-related strain infecting oilseed rape in Poland. References: (1) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (2) A. C. Padovan et al. Aust. J. Grape Wine Res. 1:25, 1995. (3) M. Starzycki and E. Starzycka. Oilseed Crops 21:399, 2000. (4) Y. Zhao et al. Int. J. Syst. Evol. Microbiol. 59:2582, 2009.

Incidence and severity of Huanglongbing (HLB) disease were assessed in Apr. 2010 among eight citrus cultivars representing diverse scion types growing in commercial groves in Florida's Indian River region, an area with a high incidence of HLB. In each grove, 20 trees of each cultivar were rated for visual HLB symptoms and leaves were collected for quantitative polymerase chain reaction quantification of Candidatus Liberibacter asiaticus (CLas), the presumptive causal agent of HLB. There was a strong correlation between HLB rating and CLas titer (titer represented by Ct, r2 = 0.37 and 0.40, for whole tree and leaf sample, respectively, both with P < 0.0001) across all cultivars and groves. Although incidence and severity of HLB varied considerably among the groves, scion-specific differences were apparent, even when analyses excluded potentially confounding grove effects. ‘Temple’ tangor showed the most consistently low incidence of HLB symptoms and CLas titer; in contrast, ‘Murcott’ tangor and ‘Minneola’ tangelo had the highest incidence of HLB symptoms and highest CLas titer. These results suggest useful resistance to HLB with reduced symptoms and reduced CLas titer may be found in conventional scion cultivars and further work is needed to assess this potential and its commercial value.