Epidemiology of Raspberry Bushy Dwarf Virus in the Czech Republic

Extensive monitoring of the raspberry bushy dwarf virus (RBDV) in cultivated raspberry, wild raspberry and blackberry was conducted in 1994‐99. RBDV was revealed by ELISA in 31.6% of field samples, 15.7% plants in germplasm collections and in 43.8% of propagated plants. Infected cultivars were Aborigen, Balzam, Brigantina, Bulharský Rubín, Canby, Comox, F‐103, Findus, Gatineau, Glen Moy, Granát, Heritage, Lloyd George, M‐101, Mája, Meeker, Norfolk Giant, Norna, NS?‐1D‐101, Skeena, Trent, Veten, ZamatoS? and Zeva. The virus was detected in 6.5 and 6.7% of wild raspberry and wild blackberry plants, respectively, at 22.8% and 11.4% of sampled locations. Vegetatively propagated plants seem to be the main source for virus spread in cultivated raspberry, rather than naturally infested wild Rubus populations.     

Association of raspberry bushy dwarf virus with raspberry yellows disease; reaction of Rubus species and cultivars, and the inheritance of resistance.

The agent of raspberry yellows disease is transmitted by grafting but not by aphids and is resistant to thermotherapy. Further studies showed that it is transmitted by inoculation of sap through seed; it is probably transmitted to plants by pollination. Raspberry bushy dwarf virus (RBDV) shares all these attributes and is known to infect all yellows-sensitive raspberry cultivars except Puyallup and Sumner; however, neither of these cultivars has been tested by graft inoculation with RBDV. RBDV commonly infects plants symptomiessly, even those of yellows-sensitive cultivars, but it induced yellows when inoculated either manually to Norfolk Giant raspberry or by grafting to a yellows-sensitive raspberry selection. The evidence suggests that RBDV is the causal agent of yellows disease but that symptom expression is greatiy dependent on genetic and environmental factors. Many red raspberry cultivars are resistant, probably immune, to the type culture of RBDV and this character was shown to be conferred by a single dominant gene designated Bu.     

Biological and biochemical properties of an isolate of cherry rasp leaf virus from red raspberry

A mechanically transmissible virus obtained from symptomless plants of a red raspberry selection imported into Scotland from Quebec, Canada was indistinguishable serologically from a cherry isolate of cherry rasp leaf virus (CRLV). The raspberry isolate, CRLV-R, was graft transmitted to several virus indicator species and cultivars of Rubus without inducing noticeable symptoms. In Chenopodium quinoa sap, CRLV-R lost infectivity after dilution to 10^-5 or heating for 10 min at 60°C but was infective after 16 days (the longest period tested) at 18°, 4° or - 15°C. The virus particles are isometric, c. 28 nm in diameter, and were purified with difficulty from infected C. murale and C. quinoa plants. The particles comprise two nucleoprotein components with sedimentation coefficients of 89 and 115 S and are prone to aggregate during purification. When centrifuged to equilibrium in CS₂SO₄ solution, purified virus preparations formed two major components with p= 1·28 and 1·36 g/cm³. Virus particles contained two RNA species which, when denatured in glyoxal and electrophoresed in agarose gels, had estimated mol. wt of 2·56 × 10⁶ (RNA-1) and 1·26 × 10⁶ (RNA–2). Infectivity of CRLV-R RNA was abolished by treatment with proteinase K, suggesting that the RNA is linked to protein necessary for infectivity; RNA molecules contained polyadenylate. In reticulocyte lysates, CRLV-R RNA stimulated the incorporation of ³H-leucine, mainly into two polypeptides of estimated mol. wt 200 000 and 102 000. When electrophoresed in polyacrylamide gels, protein obtained from CRLV-R particles purified by centrifugation to equilibrium in Cs₂SO₄ separated into three bands with estimated mol. wt 26 000 , 23 000 and 21 000.     

Further properties of wineberry latent virus and evidence for its possible involvement in calico disease

The flexuous filamentous particles of wineberry latent virus (WLV) were found to measure 620. 12 nm and not 510. 12 nm as previously reported. Analysis of dsRNA from infected plants detected a major species of c. 5.7. 10⁶ mol. wt and minor species of lower mol. wt. Purified virus particles formed a major and a minor buoyant density component in solutions of caesium salts with densities of 1.26 and 1.25 g cm^-3 in Cs₂SO₄ and 1.30 and 1.29 g cm^-3 in CsCl. The particles contained a single nucleic acid species, presumably single stranded RNA, and a single polypeptide of estimated mol. wt 2.78. 10⁶ and 31 000 respectively. In indirect ELISA, purified particles of WLV and particles in plant sap failed to react specifically with antiserum to nine carlaviruses, 12 potexviruses, three capilloviruses or apple chlorotic leafspot closterovirus, nor was WLV found to react with several of these antisera in immunosorbent electron microscopy or immunoblots. In Marion and Olallie blackberry, WLV in mixture with raspberry bushy dwarf virus (RBDV), but not RBDV alone, induced veinal line-pattern symptoms resembling those of calico disease reported from the USA.     

Isolates of raspberry bushy dwarf virus differing in Rubus host range

Isolates of raspberry bushy dwarf virus (RBDV) occurring in the field at East Mailing Research Station (EMRS), and an isolate from raspberry seed imported from the USSR, were found to differ from the Scottish type isolate (D200) of RBDV in that they infected red raspberry cultivars that are resistant, possibly immune, to isolate D200. Of several red raspberry, blackberry and hybrid berry cultivars and EMRS raspberry selections graft-inoculated with these recently discovered RBDV isolates only two raspberry cvs (Haida and Rannaya Sladkaya) and one EMRS selection did not become infected. Differences in the conclusions reached in two previous studies on the inheritance of resistance to RBDV in raspberry can be explained by the use of virus isolates that differed in Rubus host range.     

Natural infection with raspberry bushy dwarf virus (RBDV) of the putatively RBDV-resistant red raspberry cultivar Glen Moy, and the demonstration that it does not contain the RBDV resistance gene, Bu

When released to commerce in 1981, the red raspberry cv. Glen Moy was reported to be immune to the Scottish type isolate of raspberry bushy dwarf virus (RBDV-D200). Field observations of this cultivar in localities where RBDV was prevalent tended to support this claim of its resistance, but in the past 6–10 yr, RBDV infection has been reported in this cultivar in Australasia, USA and in several commercial crops in England. Therefore, experiments were made to investigate the reason(s) for this apparent anomaly using RBDV-infected material, putatively of cv. Glen Moy, from two locations in southern England and one each from Australia, New Zealand (NZ) and the USA. Genetic fingerprinting of genomic DNA from samples of these five RBDV-infected raspberry sources confirmed their identity as cv. Glen Moy. Comparisons of some serological and genomic properties of the five Glen Moy RBDV isolates indicated that, whilst they shared many properties with previously well characterised isolates of this virus, they were distinguishable from them. Characterisation of the isolate from NZ maintained in raspberry showed that it did not have a Rubus host range characteristic of resistance-breaking (RB) isolates, indicating that for this location, and probably also for those of Australia and the USA, RB isolates were not the cause of infection in cv. Glen Moy. When virus-tested plants of cv. Glen Moy and 45 progeny seedlings from the cross between cv. Glen Moy and the RBDV-susceptible cv. Autumn Bliss were graft inoculated with RBDV-D200, all grafted plants became infected indicating that cv. Glen Moy does not contain the RBDV resistance gene, Bu. Possible reasons for the previously reported resistance of cv. Glen Moy to RBDV are discussed.     

Spread of raspberry bushy dwarf virus by pollination, its association with crumbly fruit, and problems of control

Raspberry bushy dwarf virus (RBDV) was transmitted to raspberry seed both through the pollen and through the ovule and it infected plants pollinated with infected pollen. It did not infect plants prevented from flowering, and transmission through pollen seems to be the only method of spread in the field; in the proximity of infectors, most plants became infected during the first two or three flowering seasons. Plants containing RBDV showed no obvious symptoms, but healthy or infected flowers pollinated with infected pollen produced ‘crumbly’ fruit, containing a high proportion of aborted drupelets. RBDV was difficult to eliminate from infected raspberry by heat therapy. Raspberry cultivars that fail to become infected naturally were also immune to infection by grafting. Use of immune cultivars offers the only method of control and, because infected plants may produce crumbly fruit, future cultivars should if possible possess immunity to RBDV.     

The occurrence and distribution of isolates of raspberry bushy dwarf virus in England

The distribution of distinct isolates of raspberry bushy dwarf virus (RBDV) in Rubus in England was studied. Isolates similar in Rubus host range to the Scottish type isolate (D200) were largely confined to the old red raspberry (Rubus idaeus) cv. Norfolk Giant, but were also encountered in a single plant of an unidentified raspberry cultivar and in a clump of wild R. idaeus. Outside East Mailing Research Station (EMRS) RBDV isolates with wider Rubus host ranges than that of the type isolate were found only and exclusively in hybrid berries (Loganberry, clones LY59 and L654, and Tayberry) in which infection ranged from < 1% to 100%. The significance of these findings is discussed.     

Infectibility and sensitivity of UK raspberry, blackberry and hybrid berry cultivars to Rubus viruses

Six blackberry or hybrid berry cultivars and 19 raspberry cultivars were assessed for their infectibility with, and sensitivity to, graft inoculation with 10 distinct viruses found infecting Rubus in the UK. Cultivars were grafted with each of, two isolates of the pollen borne raspberry bushy dwarf virus (RBDV), five aphid borne viruses: black raspberry necrosis, raspberry leaf mottle (RLMV), raspberry leaf spot (RLSV), rubus yellow net and raspberry vein chlorosis (RVCV); and isolates of the nematode transmitted nepoviruses, arabis mosaic, raspberry ringspot, strawberry latent ringspot and tomato black ring. All tested cultivars were infectible with a resistance breaking isolate of RBDV but only about half of that number with the Scottish type isolate of the virus. The raspberry cvs Autumn Bliss, and occasionally Glen Garry and Glen Prosen, developed leaf yellowing symptoms following infection with RBDV, but none of the other infected cultivars showed obvious leaf symptoms when kept in a heated glasshouse during the growing season. All tested cultivars were infectible with each of the four viruses transmitted in nature by the aphid, Amphorophora idaei. Most were infected symptomlessly, but seven cultivars developed severe leaf spotting symptoms due to infection with RLMV or RLSV. All but one of the raspberry cultivars were infectible with RVCV, which is transmitted in nature by the aphid Aphis idaei, and almost all infected plants developed leaf symptoms; only one of the hybrid berry or blackberry cultivars tested was infected with RVCV. In tests with the four nepoviruses, all tested cultivars, except Tummelberry, were infectible with at least one or more of these viruses. However, cultivars responded differently to challenge inoculation with different isolates of individual nepoviruses. Several cultivars developed chlorotic leaf mottling following infection with some nepovirus isolates. The implications of these results for virus control are discussed in the light of the changing pattern of virus and virus vector incidence in the UK.     

Purification and properties of Australian lucerne latent virus, a seed-borne virus having affinities with nepoviruses

An isolate of Australian lucerne latent virus (ALLV) from lucerne in New Zealand was mechanically transmitted to a few herbaceous hosts. It induced diagnostic symptoms in several species of the Chenopodiaceae, but was symptomless in most other hosts including lucerne and Trifolium subterraneum. It was seed transmitted in lucerne. When assayed to Chenopodium quinoa, infective C. quinoa sap lost infectivity after diluting to 10^-4, heating for 10 min at 55°C and storage for 4 days at 4°C. ALLV was purified from infected C. quinoa or pea plants by extracting sap in 0.1 m borate buffer (pH 7) containing 0.2% 2-mercaptoethanol and clarifying with 15% bentonite suspension, high and low speed centrifugation and sucrose density gradient centrifugation. Purified virus preparations contained isometric particles about 25 nm in diameter and sedimented as three virus components with sedimentation coefficients (s_20-w⁰) of 56 S, 128 S and 133 S. The 56 S component appeared to consist of nucleic acid-free protein shells. Polyacrylamide gel electrophoresis of virus preparations showed that ALLV contained a single protein species of mol. wt 55 000 and two RNA species of mol. wt 2.1 × 10⁶ and 2.4 × 10⁶. An antiserum to ALLV had an homologous titre of 1/256 to purified virus but failed to detect ALLV in infective sap of C. quinoa, pea or lucerne. Purified ALLV failed to react to antisera to 28 distinct isometric plant viruses including those to 10 nepoviruses.     

Virus infections reduce in vitro multiplication of ‘Malling Landmark’ raspberry

Summary Virus-infected plants are often symptomless and may be inadvertently used as explant sources in tissue culture research. Our objective was to determine the effect of virus infection on micropropagation. We studied the effects of single and multiple infections of three common raspberry viruses on the in vitro culture of ‘Malling Landmark’ red raspberry (Rubus idaeus L.). Virus-infected reaspberry plants were produced by leaf-graft inoculation from known-infected plants onto virus-free ‘Malling Landmark’. Single-virus source plants were infected with either tobacco streak ilarvirus (TSV), tomato ringspot nepovirus (TomRSV), or raspberry bushy dwarf idaeovirus (RBDV) and were free of other viruses as determined by enzyme-linked immunosorbent assay (ELISA) and bioassay. Virus-free, single, and multiple virus-infected ‘malling Landmark’ explants were initiated into culture and multiplied on Anderson's medium with 8.9 μM N⁶-benzyladenine (BA). At the end of the multiplication tests, ELISA reconfirmed virus infections. In vitro multiplication of ‘Malling Landmark’ was significantly reduced by multiple infections, and multiplication of plants infected with all three viruses (RBDV+TomRSV+TSV) was less than half that of virus free cultures. Shoot height and morphology of in vitro cultures were not influenced by virus infection. The greenhouse stock plant with the three-virus infection was stunted and yellow compared to the control and the other infected plants. Part of a thesis submitted by C.-W.V.T. in partial fulfilment of the requirements for the MS degree. The use of trade names in this publication does not imply endorsement by the U.S. Department of Agriculture or Oregon State University.     

Chenopodium necrosis: a distinctive strain of tobacco necrosis virus isolated from river water

A distinctive strain of tobacco necrosis virus (TNV) of unknown source was repeatedly isolated from water of the River Avon (Warwickshire) and two of its tributaries (R. Swift and R. Alne) using a technique developed for the concentration and isolation of water-borne bacteriophages. The same strain was isolated from the rivers Cam and Thames and from Lake Esthwaite (Cumbria) together with tomato bushy stunt virus. The TNV strain, designated Chenopodium necrosis (TNV-CN) was mechanically transmissible to C. amaranticolor and C. quinoa in both of which it caused local lesions and systemic infection. TNV-CN caused no infection when inoculated to tobacco (Nicotiana tabacum cv. White Burley) plants. The virus was not adsorbed to soil, could be isolated from leachate of soil in which systemically infected C. quinoa were grown and C. quinoa plants became infected when grown in soil watered with suspensions of the virus. The virus was not transmitted by Myzus persicae but was vectored by the zoospores of a lettuce isolate of Olpidium brassicae. TNV-CN was infective after 10 min at 85 °C., 3 wk at 20 °C and when diluted to 10^-8 but not 10^-9. Purified virus preparations contained c. 26 nm isometric virus particles. TNV-CN contained single-stranded RNA (mol. wt 1·5 × 10⁶) and one protein (mol. wt c. 26·4 × 10³) which co-electrophoresed in polyacrylamide gels with the protein of the D strain of TNV (TNV-D). Analytical centrifugation of TNV-CN indicated a single component virus with the same sedimentation coefficient (s₂₀, w= 115S) and buoyant density (1·385) in a CsCl gradient as those of TNV-D. TNV-CN and TNV-D were indistinguishable serologically.     

Molecular detection and characterisation of black raspberry necrosis virus and raspberry bushy dwarf virus isolates in wild raspberries

Virus‐derived small interfering RNAs (siRNAs) were extracted from leaves of wild raspberries (Rubus idaeus) sampled from three different regions in Finland and subjected to deep sequencing. Assembly of the siRNA reads to contigs and their comparison to sequences in databases revealed the presence of the bipartite positive‐sense single‐stranded RNA viruses, raspberry bushy dwarf virus (RBDV, genus Idaeovirus), and black raspberry necrosis virus (BRNV, family Secoviridae) in 19 and 26 samples, respectively, including 15 plants coinfected with both viruses. Coverage with siRNA reads [21 and 22 nucleotides (nt)] was higher in BRNV‐FI (Finland) RNA1 (79%) than RNA2 (45%). In RBDV, the coverage of siRNA reads was 89% and 90% for RNA1 and RNA2, respectively. Average depth of coverage was 1.6–4.9 for BRNV and 16.5–36.5 for RBDV. PCR primers designed for RBDV and BRNV based on the contigs were used for screening wild raspberry and a few cultivated raspberry samples from different regions. Furthermore, the sequences of BRNV RNA1 and RNA2 were determined by amplification and sequencing of overlapping contigs (length 1000–1200 nt) except for the 3′ and 5′ ends of RNA1 and RNA2 covered by primers. RNA1 of the Finnish BRNV isolate (BRNV‐FI) was 80% and 86% identical to BRNV‐NA (USA) and BRNV‐Alyth (UK), respectively, whereas the identity of NA and Alyth was 79%. RNA2 of BRNV‐FI was 84% and 80% identical to BRNV‐NA and BRNV‐Alyth, respectively, whereas NA and Alyth were 82% identical. Hence, the strains detected in Finland differ from those reported in the UK and USA. Our results reveal the presence of BRNV in Finland for the first time. The virus is common in wild raspberries and nearly identical isolates are found in cultivated raspberries as well. The results show that wild raspberries in Finland are commonly infected with RBDV or BRNV or both viruses and thus are likely to serve as reservoirs of RBDV and BRNV for cultivated Rubus spp.     

Detection of Sap-Transmissible Viruses by ELISA in Tissue-Propagated Plants of Red Raspberry during in vitro Culture

Apple mosaic virus and raspberry bushy dwarf virus were detected by ELISA in plantlets of red raspberry still growing in vitro. The plantlets were derived from explants which were excised from plants infected by either of the viruses mentioned. Detection by ELISA of prune dwarf virus in 4-month-old in vitro cultures of sour cherry was reported earlier. Thus, application of ELISA to tissue cultured plants in vitro seems to be an appropriate method for early detection of virus-infected plant cultures.     

Purification and some properties of strawberry mottle virus

Strawberry mottle virus (SMoV) (three isolates: HJ, 3E and N) were transmitted to Chenopodium quinoa plants by sap inoculation. All three isolates induced very similar symptoms consisting of chlorotic spots and ringspots in inoculated leaves, and vein chlorosis, mottling, and dwarfing of the upper leaves. SMoV isolate HJ was purified from infected C. quinoa by homogenisation with 10 mM phosphate buffer, pH 7.2 containing 5% Triton X-100, followed by differential, sucrose density-gradient and CsCl equilibrium density-gradient centrifugations. A fraction with a buoyant density of 1.42g^- cm^-3 after CsCl density-gradient centrifugation was highly infectious to C. quinoa and contained many isometric virus-like particles c. 37 nm in diameter. These virus-like particles were never found in fractions from uninfected preparations. Electrophoretic analysis of a fraction containing virus-like particles revealed that these particles might have a single coat protein subunit with the apparent molecular mass of 26 K daltons and one nucleic acid of 6.6 kilobases. Double-stranded RNA analysis of isolate HJ-infected or uninfected C. quinoa and Fragaria vesca var. semperflorens seedling line ‘Alpine’ plants showed that both infected plants had two infection-specific dsRNA bands of mol. wts 4.5 and 3.9 × 10⁶.     

Purification and properties of elderberry latent virus, one of four sap-transmissible viruses obtained from American elder (Sambucus canadensis L.)

Cherry leaf roll, tomato black ring and two previously unrecorded viruses were transmitted to Chenopodium quinoa from Sambucus canadensis plants imported from the U.S.A. Of the two newly recognized viruses one, code-named elderberry virus A, has filamentous particles about 650 times 15 nm; the other, named elderberry latent virus (ELV), was transmitted to several herbaceous species but remained symptomless in elder and most other hosts. In C. quinoa sap ELV lost infectivity after dilution to 10^--⁵ to 10^-- ⁶ , 10 min at 85–90°C, and 7 days at 18°C. Infectivity of nucleic acid extracts was abolished by ribonuclease in 0.2 m sodium chloride. ELV was purified from C. quinoa leaf extracts that were clarified with chloroform, by precipitation at pH 5 and differential centrifugation. Purified preparations contained numerous isometric particles c. 30 nm in diameter and a few particles c. 17 nm in diameter. In 0.06 M phosphate buffer ELV sedimented as a major 112 S (calculated for infinite dilution) component and a 48 S minor component. ELV showed no serological relationship to twenty-seven other isometric plant viruses. Its present cryptogram is R/I: *I*:S/S:S/*.     

Purification and properties of blackberry chlorotic ringspot, a new virus species in subgroup 1 of the genus Ilarvirus found naturally infecting blackberry in the UK

A mechanically transmissible virus was isolated from Bedford Giant blackberry plants showing chlorotic mottling and ringspot symptoms growing in Scotland. It infected several herbaceous test plants, many of them symptomlessly. This virus was also transmitted to several Rubus species and cultivars by graft inoculation with scions from the field‐infected Bedford Giant plant. Most grafted plants were infected symptomlessly, but Himalaya Giant blackberry and the hybrid berry Tayberry developed symptoms similar to those in the infected Bedford Giant plant. In the sap of infected Chenopodium quinoa, the virus lost infectivity when diluted 10^?4 but not 10^?3, after 6 h and 48 h when kept at 20°C and 4°C, respectively, but was infective for more than 8 days when kept at ?15°C. Preparations of purified virus from infected C. quinoa or spinach sedimented as three major nucleoprotein components and consisted of quasi‐isometric particles that varied in size from 24 to 32 nm in diameter and that were not penetrated by negative stain. Such virus particle preparations contained a major polypeptide of ca 28 kDa and three single‐stranded RNA species of estimated size 3.2, 2.8 and 2.1 kb. The complete sequence of the largest RNA (RNA 1, 3478 nt) and the partial sequence of the other RNAs (1863 and 2102 nt long, respectively) were determined and compared with sequences in databases. These findings, together with the biological and biochemical properties of this virus, indicate that it should be regarded as a distinct species in subgroup 1 of the genus Ilarvirus even though it was serologically unrelated to existing members of this subgroup. The virus showed a very distant serological relationship with prune dwarf virus (PDV) but differed significantly from it in the amino acid sequence of its coat protein, experimental host range and symptomatology and was unrelated to PDV at the molecular level. The virus, tentatively named blackberry chlorotic ringspot virus, is therefore a newly described virus and the first ilarvirus found naturally infecting Rubus in the UK.     

Properties, relationships and transmission of a strain of raspberry ringspot virus infecting raspberry cultivars immune to the common Scottish strain*

Plants of Lloyd George and Seedling M raspberry (Rubus idaeus L.) were found in eastern Scotland infected with raspberry ringspot (RRV), a virus to which these varieties were previously considered immune. Most RRV isolates from affected plants caused milder symptoms in herbaceous test plants than did the type isolates of the common Scottish and English strains. In graft-transmission tests the Lloyd George strain of RRV infected all the raspberry cultivars tested, including those immune to the common Scottish strain. No consistent differences were found between isolates of the two strains in in vitro properties or serological behaviour. Both strains were transmitted in seed of Stellaria media and in soil containing Longidorus elongatus. Possible reasons why the new strain is uncommon in Scotland are discussed.     

Propagation of black raspberry necrosis virus (BRNV) in mixed culture with solanum nodiflorum mottle virus, and the production and use of BRNV antiserum

The concentration of particles of black raspberry necrosis virus (BRNV), which is normally extremely low in herbaceous plants, increased about 1000-fold when Nicotiana clevelandii plants were inoculated with a mixture of BRNV and an unrelated virus, solanum nodiflorum mottle (SNMV). In sap from N. clevelandii infected with the mixed culture, BRNV infectivity survived dilution to 10?⁴ but not 10?⁵, and storage for 6 but not 8 days at 20 ^oC, for 6 but usually not 10 days at 4 ^oC and for more than 13 days at – 15 ^oC. When plants were inoculated with the mixed culture, BRNV induced typical symptoms in several Chenopodium species and infected several previously unreported hosts. Purified preparations of particles of the mixed culture contained only a small proportion of BRNV particles, which sedimented in sucrose density gradients as two components, one, probably non-infective, of c. 505, and the other, infective, of 120-130S. An antiserum prepared to purified particles of the mixed culture was cross-absorbed with SNMV particles and used in indirect ELISA to detect BRNV in herbaceous plants infected with the mixed culture, and also in a wide range of Rubus species, cultivars and hybrids infected naturally, by grafting or by inoculation with the aphid Amphorophora idaei. The reliability of ELISA for detecting BRNV in raspberry leaves depended on the cultivar and time of year. Some cultivars, such as Glen Clova, had low concentrations of BRNV, which was detected reliably only in late spring/early summer, whereas other cultivars, such as Lloyd George and Mailing Enterprise, had greater BRNV concentrations. In small-scale surveys in eastern Scotland, BRNV was detected by ELISA in many raspberry cvs, including some that contain major gene resistance to the vector, A. idaei; in five of nine raspberry stocks entered for the Standard grade certificate but in none of five stocks entered for the Stock Cane certificate; and in 40% of wild raspberry and 14% of wild bramble plants growing near commercial raspberry crops. The significance of these findings for the control of BRNV is discussed.     

Incidence and genetic diversity of raspberry bushy dwarf virus (RBDV) in Rubus spp. in Turkey

Raspberry bushy dwarf virus (RBDV), recently renamed to Idaeovirus rubi, is one of the most common viruses infecting Rubus species worldwide but there is still a limited number of genome sequences available in the GenBank database and the majority of the sequences include partial sequences of RNA-1 and RNA-2. The distribution and incidence of RBDV in main raspberry and blackberry growing provinces in Turkey were monitored during 2015–2019 and 537 Rubus spp. samples were tested by both DAS-ELISA and RT-PCR. Among the tested samples, 36 samples tested positive for RBDV by DAS-ELISA and 67 samples by RT-PCR. There was relatively low nucleotide diversity among the Turkish isolates. Turkish isolates shared 93%–97.7%, 84.3%–98.9%, and 85%–99.2% nucleotide sequence identities with available sequences in the GenBank, in partial RNA-1, movement protein (MP) and coat protein (CP) genes, respectively. In the phylogenetic tree constructed for RNA-1, MP, and CP sequences, all Turkish raspberry isolates were clustered in a distinct clade. However, the blackberry isolates showed considerable variation in nucleotide sequences and were placed in three distinct groups. The divergent blackberry isolates showed high variability in MP (84.5%–89.3%) and CP (85.5%–89.7%) regions and were placed in a distinct group. The rest of blackberry isolates clustered together with sweet cherry RBDV isolates adjacent to the grapevine clade or together with raspberry isolates. The comparative analysis conducted on three RNA segments of RBDV highlighted the high sequence diversity of Turkish RBDV isolates. This study also emphasizes the importance of regular monitoring of RBDV infections in Turkey, with special regard to those Rubus spp. and grapevine accessions employed in conservation and selection programmes. In particular, the presence of new RBDV genetic variants and infection of Rubus species must be taken into account to choose a correct detection protocol and management strategy.