C. Lanzoni

Beet soil-borne mosaic virus RNA-4 encodes a 32 kDa protein involved in symptom expression and in virus transmission through Polymyxa betae

Beet soil-borne mosaic virus (BSBMV), like Beet necrotic yellow vein virus (BNYVV), is a member of the Benyvirus genus and both are transmitted by Polymyxa betae. Both viruses possess a similar genomic organization: RNA-1 and -2 are essential for infection and replication while RNA-3 and -4 play important roles in disease development and vector-mediated infection in sugar beet roots. We characterized a new species of BSBMV RNA-4 that encodes a 32 kDa protein and a chimeric form of BSBMV RNA-3 and -4. We demonstrated that BSBMV RNA-4 can be amplified by BNYVV RNA-1 and -2 in planta, is involved in symptoms expression on Chenopodium quinoa plants and can also complement BNYVV RNA-4 for virus transmission through its vector P. betae in Beta vulgaris plants. Using replicon-mediated expression, we demonstrate for the first time that a correct expression of RNAs-4 encoded proteins is essential for benyvirus transmission.

A Rapid Protocol of Crude RNA/DNA Extraction for RT-qPCR Detection and Quantification of 'Candidatus Phytoplasma prunorum'

Many efforts have been made to develop a rapid and sensitive method for phytoplasma and virus detection. Taking our cue from previous works, different rapid sample preparation methods have been tested and applied to Candidatus Phytoplasma prunorum (‘Ca. P. prunorum’) detection by RT-qPCR. A duplex RT-qPCR has been optimized using the crude sap as a template to simultaneously amplify a fragment of 16S rRNA of the pathogen and 18S rRNA of the host plant. The specific plant 18S rRNA internal control allows comparison and relative quantification of samples. A comparison between DNA and RNA contribution to qPCR detection is provided, showing higher contribution of the latter. The method presented here has been validated on more than a hundred samples of apricot, plum and peach trees. Since 2013, this method has been successfully applied to monitor ‘Ca. P. prunorum’ infections in field and nursery. A triplex RT-qPCR assay has also been optimized to simultaneously detect ‘Ca. P. prunorum’ and Plum pox virus (PPV) in Prunus.

Agroinoculation of Beet necrotic yellow vein virus cDNA clones results in plant systemic infection and efficient Polymyxa betae transmission

Agroinoculation is a quick and easy method for the infection of plants with viruses. This method involves the infiltration of tissue with a suspension of Agrobacterium tumefaciens carrying binary plasmids harbouring full-length cDNA copies of viral genome components. When transferred into host cells, transcription of the cDNA produces RNA copies of the viral genome that initiate infection. We produced full-length cDNA corresponding to Beet necrotic yellow vein virus (BNYVV) RNAs and derived replicon vectors expressing viral and fluorescent proteins in pJL89 binary plasmid under the control of the Cauliflower mosaic virus 35S promoter. We infected Nicotiana benthamiana and Beta macrocarpa plants with BNYVV by leaf agroinfiltration of combinations of agrobacteria carrying full-length cDNA clones of BNYVV RNAs. We validated the ability of agroclones to reproduce a complete viral cycle, from replication to cell-to-cell and systemic movement and, finally, plant-to-plant transmission by its plasmodiophorid vector. We also showed successful root agroinfection of B. vulgaris, a new tool for the assay of resistance to rhizomania, the sugar beet disease caused by BNYVV.

First Report of Prune dwarf virus and Prunus necrotic ringspot virus on Peach in Montenegro

In September and October 2011, samples were collected from mature peach trees (~17 years old) exhibiting symptoms of chlorotic rings and spots, vein clearing, mosaic, necrosis, leaf distortion, stunting, and rosette formation in a major commercial orchard (~80 ha) near Podgorica, Montenegro. Samples were collected from nine different peach varieties (cvs. Adriana, Caldesi, Gloria, Maria Marta, May Crest, Morsiani, Rita Star, Spring Belle, and Spring Crest). Samples (n = 58) were tested using DAS-ELISA for the presence of Prune dwarf virus (PDV) and Prunus necrotic ringspot virus (PNRSV). Commercial positive and negative controls were included in each ELISA (antisera and controls supplied by BIOREBA AG, Reinach, Switzerland). Only one symptomatic sample from cv. Gloria tested positive for PDV (sample reference: 399/11), a further 11 samples (cvs. Rita Star [six], May Crest [four] and Spring Crest [one]) were positive for PNRSV. Samples were also tested for Plum pox virus (PPV) by real-time RT-PCR (1). The PDV positive sample (399/11) showing mosaic was in mixed infection with PPV, as were 6 of the 11 PNRSV samples, including sample 373/11 with yellow mottling and leaf distortion symptoms. On single-infected PNRSV, sample 368/11 chlorotic line patterns and leaf deformations were observed. To confirm the presence of PDV and PNRSV, positive samples were also tested by RT-PCR. Total RNA was extracted using RNeasy Plant Mini kit (Qiagen, Hilden, Germany). RT-PCR was performed with primer pairs PDV2F/PDV1R (3) and MG1/MG2 (2) specific for PDV and PNRSV, respectively. Amplicons of the expected size, 173 bp for PDV and 675 bp for PNRSV, were obtained from corresponding ELISA-positive samples. Amplified products from three samples (PDV 399/11 and PNRSV 368/11 and 373/11) were cloned into pGEM-T Easy Vector (Promega, Madison, WI) then sent for sequence analysis (MWG-Biotech AG, Edersberg, Germany). Sequence data was compared to sequences published in GenBank. Analysis of sequence obtained from isolate 399/11 (cv. Gloria) corresponded to partial CP gene of PDV, with a high degree of similarity to isolates reported from other parts of the world ranging from 94.2 to 95.9%, showing highest similarity with isolate Ch 137 (L28145). Sequence analyses of CP gene from PNRSV isolates 368/11 (JX569825) and 373/11 (JX569826) proved to be 89.3 to 99.7% identical with corresponding sequences of isolates previously described. In particular, the Montenegrin PNRSV isolates were most closely related to Chilean NctCl.augl isolate from nectarine (EF565253). To demonstrate that the virus was infectious, seedlings of peach cv. GF305 were side grafted with bud-woods from PDV (sample 399/11) and PNRSV-positive samples (samples 368/11 and 373/11) and a healthy control sample. Grafted seedlings were kept in a greenhouse with a under 16-h light regime at 22 to 24°C and observed for symptom development. No symptoms were observed in grafted plants with the healthy control. All plants inoculated with virus-positive samples exhibited stunted vegetation and mild mottle with no difference in symptoms between the two viruses. Indicator plants of peach cv. GF305 inoculated with PPV dual-infected samples (399/11 and 373/11) were subsequently shown to be positive for PPV by real-time RT-PCR. Subsequent DAS-ELISA test on samples from experimentally inoculated trees using specific antisera as described above confirmed PDV and PNRSV infections as expected. These viruses have recently been reported from sour cherry (Prunus cerasus L.) in Serbia (4), ~600 km to the northeast. However, to our knowledge, this is the first report on the occurrence of PDV and PNRSV in Montenegro. References: (1) N. Capote et al. Int. Microbiol. 12:1, 2009. (2) M. Glasa et al. Ann. Appl. Biol. 140:279, 2002. (3) D. R. Parakh et al. Acta Hortic. 386:421, 1996. (4) S. Radičević et al. Genetika 44:285, 2012.

The phytosanitary status of the National Collection of fruits and nuts of Afghanistan and the private Mother Stock Nurseries: a virus survey

The horticultural industry is a vital component of the agriculture sector of Afghanistan, the primary engine of the country’s recovering economy which engages approximately 80% of the working population. This sector was thriving in the 1970s, but is today incapable of competing in the international market. To recover and develop the horticulture of the country, the European Community (EC) supports the PHDP (Perennial Horticulture Development Project), to provide true to type/ecotype and healthy planting materials, and the Plant Biotechnology Laboratory, to ensure the health status of local germplasm. This laboratory started screening the health status of the Afghan Germplasm National Collections in order to ensure the multiplication of not only the best-selected varieties or ecotype, but also to avoid production and distribution of virus-infected trees. Inspection for symptoms and sample collection for viral diseases was carried out in all the National Collection fields, including cherry, pear, peach, plum, apricot, almond, apple, grape and citrus plants, located in different areas of the country. Stone fruit plants infected by Apple chlorotic leaf spot virus or Prunus necrotic ringspot virus have been identified in the National Collection experimental farms located in different provinces of Afghanistan. Moreover, many grape plants included in the National Collection located in Herat and Kandahar resulted infected by Grapevine fanleaf virus, but only few imported plants by Grapevine leafroll associated virus 1, Grapevine leafroll associated virus 3 or Grapevine virus A. Finally, in Jalalabad (Nangarhar province) citrus plants showing vein flecking, yellowing and plant decline symptoms were found to be infected by Citrus tristeza virus. Some of the identified viral isolates have been characterized molecularly, amplifying a fragment corresponding to the coat protein gene from a selection of positive samples. The presence of those viruses in different accessions of the national collection is of concern for Afghan horticulture. Implementation of the certification schemes is therefore necessary to quarantine the production and for the employment of virus-free propagating material.