Ringspot symptoms in European mountain ash (Sorbus aucuparia L.), fig mosaic, rose rosette, raspberry leaf blotch, pigeonpea sterility mosaic (Cajanus cajan) and High Plains disease of maize and wheat were found to be associated with viruses that share several characteristics. They all have single-stranded multipartite RNA genomes of negative orientation. In some cases, double membrane-bound virus-like particles of 80 to 200 nm in diameter were found in infected tissue. Furthermore, at least five of these viruses were shown to be vectored by eriophyid mites. Sequences of European mountain ash ringspot-associated virus (EMARaV), Fig mosaic virus (FMV), rose rosette virus (RRV), raspberry leaf blotch virus (RLBV), pigeonpea sterility mosaic virus and High Plains virus strongly support their potential phylogenetic relationship. Therefore, after characterization of EMARaV, the novel genus Emaravirus was established, and FMV was the second virus species assigned to this genus. The recently sequenced RRV and RLBV are supposed to be additional members of this new group of plant RNA viruses.

Emaravirus: A Novel Genus of Multipartite, Negative Strand RNA Plant Viruses

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Overcoming nitrogen fertilizer over-use through technical and advisory approaches: A case study from Shaanxi Province, northwest China

The wheat curl mite (WCM), Aceria tosichella, and the plant viruses it transmits represent an invasive mite-virus complex that has affected cereal crops worldwide. The main damage caused by WCM comes from its ability to transmit and spread multiple damaging viruses to cereal crops, with Wheat streak mosaic virus (WSMV) and Wheat mosaic virus (WMoV) being the most important. Although WCM and transmitted viruses have been of concern to cereal growers and researchers for at least six decades, they continue to represent a challenge. In older affected areas, for example in North America, this mite-virus complex still has significant economic impact. In Australia and South America, where this problem has only emerged in the last decade, it represents a new threat to winter cereal production. The difficulties encountered in making progress towards managing WCM and its transmitted viruses stem from the complexity of the pathosystem. The most effective methods for minimizing losses from WCM transmitted viruses in cereal crops have previously focused on cultural and plant resistance methods. This paper brings together information on biological and ecological aspects of WCM, including its taxonomic status, occurrence, host plant range, damage symptoms and economic impact. Information about the main viruses transmitted by WCM is also included and the epidemiological relationships involved in this vectored complex of viruses are also addressed. Management strategies that have been directed at this mite-virus complex are presented, including plant resistance, its history, difficulties and advances. Current research perspectives to address this invasive mite-virus complex and minimize cereal crop losses worldwide are also discussed.

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Wheat curl mite, Aceria tosichella , and transmitted viruses: an expanding pest complex affecting cereal crops

Soil-borne viruses affecting cereals: known for long but still a threat

The threat of long-term climate change has driven a number of international and national bodies to call for a re-direction of development pathways so that they are more resource efficient and use less carbon (C) in the form of fossil fuel per unit of economic growth and cause lower greenhouse gas emissions (GHGs). Agriculture is one of the largest anthropogenic sources of GHG emissions yet few authorities take account of this fact in their proposals and programmes for low C development. Hence this policy review examines the case for promoting strategies and policies for low C agricultural growth. Most of the policy and technological options that it considers have already been put forward by the Intergovernmental Panel on Climate Change (IPCC) and others in the context of climate change mitigation, but constraints to their implementation have often been underestimated. This review reassesses their potential contribution in the light of known bio-physical, socio-economic and institutional limitations. It concludes that there is a very strong case for greatly increasing the priority given to policies for low C growth which can be true win–win–win responses. Many of them are more cost-effective than the responses available to other sectors. They can be pro-poor and have other socio-economic benefits. They not only limit GHG emissions but also provide a range of other environmental and ecosystem benefits. However there can be significant barriers to implementation that must be overcome by national policies shaped to meet the needs of different farmer groups and agricultural systems.

Low carbon agriculture: Objectives and policy pathways

An initial investigation of Potato spindle tuber viroid (PSTVd) in capsicum revealed the presence of the viroid at two sites in the Auckland area. Subsequently, a delimiting survey of PSTVd was conducted in glasshouse capsicum and tomato crops in New Zealand from April to June 2002. The viroid was not detected in any of the 59 tomato sites surveyed. PSTVd was found at a further three of 41 capsicum sites surveyed in the Auckland region. Prior to the delimiting survey, three tomato sites where PSTVd was detected in April 2001 were visited and PSTVd was still present in tomato plants at one of these sites. Seeds and flesh from fruit of diseased capsicum and tomato plants tested PSTVd positive at two sites prior to the delimiting survey. The viroid was not detected in 8-, 16- and 27-week-old seedlings grown from seeds of infected capsicum and tomato crops. The PSTVd isolate from capsicum had 100% nucleotide identity to a tomato isolate from New Zealand (GenBank accession AF369530), 98.3% to a tomato isolate from the Netherlands (GenBank accession XI7268) and 96.3% to a Solanurn isolate from Australia (GenBank accession U51895). As PSTVd has never been reported in New Zealand before, capsicum and tomato seeds are considered to be the most likely source of PSTVd infection.

Distribution of Potato spindle tuber viroid in New Zealand glasshouse crops of capsicum and tomato

High Plains virus (HPV) causes a potentially serious economic disease of cereals and is of quarantine importance for New Zealand. HPV is transmitted by the wheat curl mite Aceria tosichella, and neither the virus nor its vector is present in New Zealand. Cereal seeds imported to New Zealand are required to be certified HPV-free, as the virus is a regulated pest. A procedure was developed for inspecting plants and testing cereal seedlings in quarantine using reverse transcriptase polymerase chain reaction (RT-PCR) as a detection method. A sample of 50,655 sweet corn seeds was taken from an imported commercial line and germinated in containment. Symptomatic seedlings were collected at 3 and 4 ½ weeks after sowing. Eight out of 27 symptomatic samples tested HPV positive by RT-PCR and were confirmed by enzyme-linked immunosorbent assay (ELISA). Sequence analysis revealed that the HPV isolates had a 99.3 to 100% nucleotide identity and 99.0 to 100% amino acid similarity with the HPV USA isolate (GenBank accession no. U60141). HPV variants were detected by single stranded conformational polymorphism (SSCP) analysis but not by restriction fragment length polymorphism (RFLP).

https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PD-89-1103

Development of an RT-PCR for High Plains virus Indexing Scheme in New Zealand Post-Entry Quarantine.

Soil-borne wheat mosaic virus (SBWMV) was identified using transmission electron microscopy, enzymelinked immunosorbent assay (ELISA) with SBWMV-specific antibodies and reverse transcription-polymerase chain reaction (RT-PCR) tests with SBWMV-specific primers and sequence comparison in two out of five samples collected from a wheat (Triticum aestivum) plant showing severe leaf mosaic. The plant was also infected with Barley stripe mosaic virus and Barley yellow dwarf virus-MAV and -PAV. A further 28 out of 200 wheat samples tested positive for SBWMV using ELISA. A comparison of 11 New Zealand SBWMV isolates indicated that they were all identical and had 98% nucleotide sequence identity with SBWMV isolates from the United States, subgroup New York-Illinois. At the location of the SBWMV outbreak the vector, Polymyxa graminis, was detected by PCR and the identity was confirmed by sequencing. This is the first report of SBWMV in New Zealand.

Investigation of an outbreak of Soil-borne wheat mosaic virus in New Zealand

Impatiens necrotic spot virus (INSV) was first detected in New Zealand in August 2003 in Freesia refracta plants growing in a nursery on the South Island of New Zealand. Surveys were conducted to determine the extent of spread of the virus within the nursery and to other sites around the country. INSV was confirmed by a newly developed reverse transcription-polymerase chain reaction (RT-PCR) in impatiens (Impatiens walleriana), primula (Primula obconica) and Ranunculus sp. at the original site and in impatiens (I. walleriana) at two additional North Island sites. Infected material was destroyed and a management program established with the industry. However, in June 2006 a begonia (Begonia × tuberhybrida) specimen from a fourth North Island nursery was received which was found to be infected with INSV. Other species confirmed by RT-PCR to be infected at this site include cyclamen (Cyclamen persicum), gardenia (Gardenia jasminoides), gerbera (Gerbera jamesonii), as well as hibiscus (Hibiscus rosa-sinensis), which is a new host for INSV. Partial nucleotide sequences obtained by RT-PCR were found to be closely related to published sequences.

Investigation of Impatiens necrotic spot virus outbreaks in New Zealand

Ornamental flower bulbs are an increasingly important crop in New Zealand. In general, production is dependent on overseas breeding programmes and regular imports of propagation material, in particular from The Netherlands. Toenable the implementation of appropriate phytosanitary controls, a targeted survey was done in 2005–2006 to determine the presence of viruses in the most important bulb genera. Using serological and molecular methods, 10 viruses (Alstroemeria mosaic virus, Freesia sneak virus [syn. Freesia leaf necrosis-associated ophiovirus], Hippeastrum mosaic virus, Hyacinth mosaic virus, Nerine latent virus, Nerine yellow stripe virus, Ornithogalum virus 3, Tulip mosaic virus, Veltheimia mosaic virus and Vallota mosaic virus) were identified for the first time in New Zealand. In addition eleven new hosts of viruses reported previously in New Zealand were detected; these new associations include one not reported previously overseas (Tomato spotted wilt virus in Ornithogalum). None of the newly reported viruses cause significant diseases and it is unlikely that they will affect bulb production significantly.

B. S. M. Lebas

Papers

Distribution of Potato spindle tuber viroid in New Zealand glasshouse crops of capsicum and tomato

Development of an RT-PCR for High Plains virus Indexing Scheme in New Zealand Post-Entry Quarantine.

Investigation of an outbreak of Soil-borne wheat mosaic virus in New Zealand

Investigation of Impatiens necrotic spot virus outbreaks in New Zealand

A survey of viruses of flower bulbs in New Zealand