A. Teifion Jones

Transmission of Pigeon pea sterility mosaic virus by the Eriophyid Mite, Aceria cajani (Acari: Arthropoda)

The transmission characteristics of Pigeon pea sterility mosaic virus (PPSMV) to pigeon pea (Cajanus cajan) by its eriophyid mite vector, Aceria cajani, were studied. Nonviruliferous A. cajani colonies were established on detached healthy leaflets of a PPSMV-immune pigeon pea cultivar floating on water. The transmission efficiency of single A. cajani was up to 53% but was 100% when >5 mites per plant were used. A. cajani acquired PPSMV after a minimum acquisition access period (AAP) of 15 min and inoculated virus after a minimum inoculation access period (IAP) of 90 min. No latent period was observed. Starvation of A. cajani prior to, or following, PPSMV acquisition reduced the minimum AAP and IAP periods to 10 min and 60 min, respectively, and mites retained virus for up to 13 h. None of the mites that developed from eggs taken from PPSMV-infected leaves transmitted the virus, indicating that it is not transmitted transovarially. Taken together, these data suggest a semipersistent mode of transmission of PPSMV by A. cajani.

Black currant reversion disease — the probable causal agent, eriophyid mite vectors, epidemiology and prospects for control

Black currant reversion disease and the vector of its causal agent, the black currant gall mite Cecidophyopsis ribis, have been recognised for at least 100 years and are the two most damaging organisms of black currant crops world-wide. However, the molecular characterisation of these two organisms has begun to be determined in only the last few years. The probable causal agent of reversion disease, Black currant reversion associated virus (BRAV), belongs to the genus Nepovirus, has isometric particles c. 28 nm in diameter that contain a single major polypeptide of c. 55 KDa and two polyadenylated ssRNA species of 7700 nt and 6400 nt. Some particle preparations also contain a satellite ssRNA species of 1432 nt. Using immuno-capture RT-PCR and primers based on the genomic RNA of BRAV, this virus was shown to be closely associated with reversion disease. Analysis of Cecidophyopsis mite rDNA, identified rapidly and unambiguously the three known species on Ribes and distinguished four new ones. Resistance to the reversion agent and to the gall mite vector has been introduced into black currant and has given effective control of these respective organisms in the field. These findings and their significance for the ecology, epidemiology and control of variants of these two organisms are reviewed and discussed.

Sterility mosaic disease - the 'green plague' of pigeonpea: advances in understanding the etiology, Transmission and control of a major virus disease.

Sterility mosaic (SMD) is the most damaging disease of pigeonpea (Cajanus cajan (L.) Millsp.) in the Indian subcontinent. After seven decades of research, vital breakthroughs made on the identification, detection, and transmission of the causal agent of this major disease are enabling the development of broad-based durable resistant pigeonpea cultivars. These breakthroughs will contribute greatly to sustainable pigeonpea production and enhance the income and livelihood of poor farmers in the semiarid tropics of the Indian subcontinent. The Crop

A new badnavirus in Ribes species, its detection by PCR, and its close association with Gooseberry vein banding disease

Gooseberry vein banding disease (GVBD) affects Ribes species and cultivars worldwide. It is the second most important virus-like disease in these crops after black currant reversion disease. In this paper, we describe a bacilliform virus, Gooseberry vein banding associated virus (GVBAV), which is associated closely with GVBD, and provide evidence that GVBAV is a distinct species within the genus Badnavirus. Purified GVBAV particles were ca. 120 × 30 nm in size and contained dsDNA. The sequence of a 1.5-kb DNA fragment amplified from viral genomic DNA was similar to those of a wide range of badnaviruses and contained motifs characteristic of the RNase H domain of the badnavirus open reading frame (ORF) III polyprotein. Phylogenetic analyses suggest that GVBAV is most closely related to Spiraea yellow leaf spot virus. Using sequence derived from the polymerase chain reaction (PCR)-amplified DNA fragment, virus-specific primers were designed. These primers were used in PCR to assay for GVBAV in a range of Ribes germplasm affected with GVBD, with other unrelated virus-like diseases and viruses found in Ribes, and in healthy plants. GVBAV was detected in all of 58 GVBD-affected plants from diverse sources, but not from healthy Ribes plants nor from plants infected with other viruses.

Comparisons of some properties of two laboratory variants of Raspberry bushy dwarf virus (RBDV) with those of three previously characterised RBDV isolates

The properties of two laboratory variants of Raspberry bushy dwarf virus (RBDV), genus Idaeovirus, were compared with those of their parental sources and with two naturally occurring variants. Isolate RB is a natural variant able to overcome the resistance to RBDV present in some red raspberry cultivars. Isolate M is a serological variant from black raspberry. Laboratory variant D1, was derived from the Scottish type isolate (D200) by continuous sub-culture in Chenopodium quinoa. Laboratory variant Can-S was derived from an isolate infecting Canby red raspberry in Canada (Can) after passage through Nicotiana benthamiana. All isolates reacted with a polyclonal antiserum to isolate D200 in agarose gel double-diffusion tests but, whereas isolates D200, RB, Can and Can-S were serologically indistinguishable, the precipitin lines formed by these isolates each spurred over those formed by isolates D1 and M. All six isolates reacted strongly with the polyclonal antiserum in double antibody sandwich and plate-trapped antigen (PTA) forms of ELISA and in Western blotting (WB) and when each of four monoclonal antibodies (Mabs) to an unnamed red raspberry isolate from Canada was used to detect antigen trapped by the polyclonal antiserum. However, the virus isolates differed in their reactions to these four Mabs in PTA-ELISA and in WB. Isolates RB, Can and Can-S behaved similarly in these tests as did isolates D200 and D1, but isolate M was distinct. In herbaceous test plants, variants D1 and Can-S were readily distinguished from their parental sources and from the other two isolates by producing either no symptoms (D1) or very severe symptoms (Can-S) in hosts. Unlike all other isolates studied world-wide, Can-S failed to infect C. quinoa systemically but induced severe necrotic local lesions in this and other hosts.Reverse transcription-polymerase chain reaction was used to amplify the gene encoding the coat protein (CP) in RNA-2, and a region of the gene encoding the polymerase in RNA-1. The nucleotide sequences of the CP genes of the six isolates were > 96% identical but isolate Can-S was the most distinctive. However, the similarity between Can-S and its parent isolate (Can) was no greater than the similarity between Can-S and the other isolates, suggesting that Can-S may not have arisen as the result of a mutation from isolate Can. Sequence comparisons of parts of the polymerase gene of isolates R15, D1, D200 and Can-S showed that they were 95–98% identical.

Incidence and Distribution of Raspberry bushy dwarf virus in Commercial Red Raspberry (Rubus idaeus) Crops in Scotland

A survey was done in 1998 to determine whether Raspberry bushy dwarf virus (RBDV) was established in raspberry fruiting plantations in Scotland. Raspberry-producing holdings were selected according to geographical area and size. Samples (201), each comprising 60 shoots per stock, were obtained from 77 holdings and tested by enzyme-linked immunosorbent assay (ELISA). ELISA-positive shoots from each infected stock were grafted onto cultivar Glen Clova, which is resistant to the Scottish-type isolate of RBDV (RBDV-S), to establish whether the virus is a resistance-breaking (RB) isolate. RBDV was detected in 22% of the stocks sampled, with 2 to 80% incidence of infection. No RBDV was in any of the 40 plantations containing cultivars resistant to RBDV-S or in Glen Clova plants, which were grafted successfully with samples from 15 infected plantations, indicating that no RB isolates were detected. The percentage of infected plantations increased with time from the planting date. In order to investigate possible sources of infection, ELISA for RBDV was made in 1999 on samples of stocks of raspberry cultivars entered for the lowest certified grade (Standard Grade) in Scotland and, in 1994 to 1997, on certified stocks planted with material originating from outside Scotland. No RBDV was detected in any of the samples. RBDV was found only rarely in samples of wild raspberry in Angus and Perthshire.

Isolation and Analysis of Double-Stranded RNA in Plant Tissues to Detect Virus and Virus-Like Agents

It is an accepted premise of cell molecular biology that most, if not all, plant RNA is transcribed directly from DNA. As such, normal healthy plants should contain no double-stranded RNA (dsRNA) molecules. In practice, small amounts of dsRNA of low M r are sometimes detected in such plants but the reasons for this are not clear. However, the detection of dsRNA species of M r greater than about 1×106 usually indicates some form of abnormalitY., the most likely being the presence of an agent with an RNA genome. Most of the many plant viruses that have been described have single-stranded RNA (ssRNA) genomes and, during their replication cycle in plants, dsRNA is produced as a transitory product, although the amount of this dsRNA that accumulates at any point in time may often be very small. Replication occurs by the production of an RNA strand complimentary to that of the virus genome parts. The RNA then strands with complementary sequences to form a base-paired double-stranded template for transcription of genomic viral RNA. Complimentary strands should therefore be equal in size to the individual genomic component strand(s) from which they were made, and the dsRNA of these species will be twice that size. However, at any point in time during the replication process in plant cells, there will be various extents of double-strandedness. On disruption of plant cells for nucleic acid extraction, the single-stranded arms of these ‘intermediate’ dsRNA forms will be destroyed by ribonucleases, leaving less than full length sized dsRNA. These ‘incomplete’ dsRNA species are termed replicative intermediates (RI) in contrast to the full length replicative forms (RF).