Surveys reveal a complex association of phytoplasmas and viruses with the blueberry stunt disease on Canadian blueberry farms

Surveys for phytoplasmas and viruses were conducted during September 2014 and 2015 on highbush blueberry farms in the Région Montérégie, Quebec. Total DNA and RNA were extracted from blueberry bushes showing blueberry stunt (BBS) symptoms and from symptomless blueberry bushes, and utilised as templates for PCR and RT‐PCR assays, respectively. Phytoplasma DNA was amplified with universal phytoplasma primers that target the 16S rRNA, secA and secY genes from 12 out of 40 (30%) plants tested. Based on 16S rRNA, secA and secY gene sequence identity, phylogenetic clustering, actual and in silico RFLP analyses, phytoplasma strains associated with BBS disease in Quebec were identified as ‘Candidatus Phytoplasma asteris’‐related strains, closely related to the BBS Michigan phytoplasma strain (16SrI‐E). The secY gene sequence‐based single nucleotide polymorphism analysis revealed that one of the BBS phytoplasma strains associated with a leaf marginal yellowing is a secY‐I RFLP variant of the subgroup 16SrI‐E. Two viruses were detected in blueberry bushes. The Blueberry Red Ringspot Virus (BRRV) was found in a single infection in the cultivar Bluecrop with no apparent typical BRRV symptoms. The Tobacco Ringspot Virus (TRSV) was found singly infecting blueberry plants and co‐infecting a BBS phytoplasma‐infected blueberry cv. Bluecrop plant. This is the first report of TRSV in the cv. Bluecrop in Quebec. The Quebec BBS phytoplasma strain was identified in the leafhopper Graphocephala fennahi, which suggests that G. fennahi may be a potential vector for the BBS phytoplasma. The BBS disease shows a complex aetiology and epidemiology; therefore, prompt actions must be developed to support focused BBS integrated management strategies.     

Development of PCR Diagnostic System for Detection of the Seed-Transmitted Tobacco Ringspot Virus in Quarantine

Tobacco ringspot virus (TRSV) is a plant quarantine virus in Korea. As such, a TRSV examination is conducted when importing various crops. In this study, RT-PCR and nested PCR systems for TRSV detection in quarantine sites, and the modified-positive control plasmid for proving laboratory contamination and false positive reactions were developed. The developed diagnostic system was used to detect TRSV in the quarantine site. It revealed that from 2012 to August 2014, a total of 12 cases were detected in imported various crops. The system is expected to continue contributing to TRSV detection in plant quarantine.

Electronic supplementary material

The online version of this article (doi:10.1007/s12088-015-0518-8) contains supplementary material, which is available to authorized users.     

Silicon delays Tobacco ringspot virus systemic symptoms in Nicotiana tabacum

Soluble silicon (Si) provides protection to plants against a variety of abiotic and biotic stress. However, the effects of Si on viral infections are largely unknown. To investigate the role of Si in viral infections, hydroponic studies were conducted in Nicotiana tabacum with two pathogens: Tobacco ringspot virus (TRSV) and Tobacco mosaic virus (TMV). Plants grown in elevated Si showed a delay in TRSV systemic symptom formation and a reduction in symptomatic leaf area, compared to the non-supplemented controls. TRSV-infected plants showed significantly higher levels of foliar Si compared to mock-inoculated plants. However, the Si effect appeared to be virus-specific, since the element did not alter TMV symptoms nor did infection by this virus alter foliar Si levels. Hence, increased foliar Si levels appear to correlate with Si-modulated protection against viral infection. This is all the more intriguing since N. tabacum is classified as a low Si accumulator.