Plant Viruses Transmitted by Thrips

All thrips (order Thysanoptera) that are known to be vectors of plant viruses are identified and described. Thrips transmit plant viruses in the Tospovirus, Ilarvirus, Carmovirus, Sobemovirus and Machlomovirus genera. Tospoviruses are the cause of a number of significant emerging diseases, such as capsicum chlorosis and scape blight of onion. They infect thrips as well as plant hosts and the relationship between pathogen and vector is intimate. Once infected at the larval stage, adult thrips usually transmit tospovirsuses for life. Transmission to plant hosts occurs when thrips feed. Information on the distribution and hosts of all recognised thrips vectors is provided. Fourteen tospovirus species are described with information provided on other tospoviruses that have not yet been designated as species. The history of the research that has led to present knowledge is reviewed in chronological order for each tospovirus. The possible origin of tospoviruses is discussed. Information is presented on viruses, which are thrips-transmitted by mechanical processes, in other genera. Pathways of spread of thrips vectors in relation to the threat of tospoviruses to European agriculture are discussed.     

The role of weeds in the epidemiology of pospiviroids

Many weeds that are closely associated with horticultural activities are known as natural reservoirs of plant viruses. However, whether these weeds can also serve as hosts of pospiviroids is not well known. Pospiviroids are naked, non‐coding RNA pathogens that cause severe economic damage in many solanaceous crops. In this study, we examined the overall risk of pospiviroid spreading from weeds to economically important crops, by combining the results from previous inoculation studies with new results coming from a survey, a contact experiment and an inoculation experiment. A survey of commercial ornamental glasshouses revealed that ornamental plants mainly belonging to the Solanaceae harbour pospiviroids, in contrast to weed species sampled in the same places. No new weed hosts could be identified after testing weeds that grew in contact with Tomato apical stunt viroid (TASVd)‐infected plants of tomato (Solanum lycopersicum) and jasmine nightshade (Solanum jasminoides) in an experimental glasshouse. Finally, in mechanical inoculation experiments with TASVd, none of the six tested weed species were determined to be a host at 6 weeks after inoculation. Commonly occurring weed species therefore do not appear to play a significant role as reservoir hosts for pospiviroids. This does not rule out other potential weed hosts that have not yet been tested. Inoculation studies should include rigorous experimental protocols with a sufficient number of replicated as well as adequate positive controls. The information gained through this study may prove useful in future risk assessments for the pospiviroid group.     

Plant Viruses Transmitted by Whiteflies

One-hundred and fourteen virus species are transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia transmit three species each. B. tabaci and T. vaporariorum are present in the European–Mediterranean region, though the former is restricted in its distribution. Of the whitefly-transmitted virus species, 90% belong to the Begomovirus genus, 6% to the Crinivirus genus and the remaining 4% are in the Closterovirus, Ipomovirus or Carlavirus genera. Other named, whitefly-transmitted viruses that have not yet been ranked as species are also documented. The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution. Entries are also annotated with references. Whitefly-transmitted viruses affecting plants in the European–Mediterranean region have been highlighted in the text.     

PM 8/5 (1) Quercus

Specific scope

The purpose of the EPPO Standard on Quercus is to recommend to EPPO Member Governments the phytosanitary measures which they should use or require for Quercus plants and plant products moving in international trade to prevent the introduction and spread of quarantine pests. Some of these recommendations are addressed to all EPPO Member Governments, others are addressed only to countries considered to face a certain level of risk from the introduction and spread of the regulated pests concerned. All these recommendations were derived from:

• EPPO Standards PM 1/2 (EPPO A1 and A2 lists) and the former EPPO Standards PM 2 (pest‐specific phytosanitary measures), or
• Pest Risk Analysis (PRA) carried out or reviewed by EPPO, or
• the Working Party on Phytosanitary Regulations.

For wood packaging material, recommendations are based on ISPM 15 Regulation of wood packaging material in international trade.

Specific approval and amendment

First approved in 2010‐09 as PM 8/3 Quercus and Castanea. Revised and approved as a separate Standard PM 8/5 in 2017‐09     

Investigation of wheat as a trap crop for control of Orobanche minor

Orobanche minor is a parasitic weed that attaches to the roots of red clover (Trifolium pratense) and a number of other broad‐leaved plant species in the Pacific Northwest USA. Orobanche minor seed must be stimulated by host plant exudates for germination and attachment to occur. However, plant species called false‐hosts can stimulate parasitic seed germination without attachment. These species could be utilized as trap crops to reduce the amount of parasitic seed in infested soil. Wheat (Triticum aestivum), was found to be a false‐host of O. minor; therefore, growth chamber, glasshouse and field soil experiments were conducted to evaluate the effect of six soft white winter wheats (T. aestivum), one durum wheat (Triticum turgidum), and one triticale (Triticale hexaploide) on O. minor germination. In growth chamber experiments, wheat and triticale induced 20–70% of O. minor seeds to germinate. In glasshouse studies, O. minor attachment was minimal on red clover plants grown in pots previously planted to wheat or triticale. In pots that did not receive a false‐host treatment, red clover plants averaged 4.2 O. minor attachments per plant. Red clover plants also had fewer O. minor attachments when grown in field soil taken from the plots where wheat or triticale were grown compared with plants grown in soil where no wheat or triticale were previously grown. Our results demonstrate that wheat may have the potential to be effectively integrated into an O. minor management system.     

Diversity and detections of Phytophthora species from trade and non‐trade environments in Ireland

The genus Phytophthora is one of the genera of organisms that poses the most threat to plant health worldwide. Statutory monitoring for Phytophthora species focuses on the species regulated in the European Union and recommended for regulation by EPPO (Plant Health Directive 2000/29 EC and the EPPO A2 List). This research provides details of the Phytophthora species detected from trade and non‐trade environments in Ireland between 2013 and 2015. The results of statutory surveys for the regulated species Phytophthora ramorum, Phytophthora kernoviae and Phytophthora lateralis from 2003 to 2015 are also presented. Testing of more than 11 000 samples was carried out using morphological and/or DNA identification with specifically designed Phytophthora conserved primers. This led to the detection of 19 species and 3 informally designated taxa of Phytophthora, including 8 new records for Ireland. Eight species were found in both trade and non‐trade locations, and three informally designated taxa were also detected. Phytophthora ramorum was found on the most hosts (30 hosts), followed by Phytophthora syringae (6 hosts) and Phytophthora kernoviae (3 hosts). Rhododendron was the host on which Phytophthora species were most frequently detected (12 Phytophthora species). The role of the plant trade in spreading invasive Phytophthora species is discussed.     

Whiteflies on tomato crops in Portugal*

In Portugal during the 1960/1980s, there was intensive development of vegetable crop production, in particular protected crops, of which tomato was the most important. The main producing regions now are Ribatejo e Oeste, Alentejo and Algarve. Tomato presents extensive phytosanitary problems, being host to a wide range of pests, including the whiteflies Trialeurodes vaporariorum, in protected crops, and Bemisia tabaci, in protected and field crops. Portugal has applied for the status of an EU ‘protected zone’ for this latter pest. As B. tabaci is an important vector of a large number of viruses, including tomato yellow leaf curl viruses (TYLCV), a monitoring programme of the tomato crop was implemented in Portugal. Preliminary data are presented concerning B. tabaci in the three main tomato‐growing regions of the country.     

昆虫与弹状病毒互作的研究进展

近年来宏基因组学研究的普及大大丰富了人们对RNA病毒多样性的认识,但对这些新发现病毒的生物学特性却所知甚少。本文围绕RNA病毒中一类重要的负单链RNA病毒--弹状病毒与其昆虫寄主互作的研究进行综述,总结已发现的弹状病毒及其昆虫寄主类型,共有20个属144种弹状病毒可以感染14个属的昆虫;根据已有的系统进化研究对弹状病毒的寄主起源进行推测;并以感染黑腹果蝇Drosophila melanogaster的sigma病毒(Drosophila melanogaster sigma virus,DMelSV)为主要对象,就弹状病毒引起的CO2麻痹致死症状以及昆虫寄主对其的免疫反应研究进行总结,而在对黑腹果蝇的研究中发现很多非经典免疫通路中的新抗病毒基因,暗示存在新的抗病毒免疫通路;通过飞虱、叶蝉与其传播的植物弹状病毒以及长须罗蛉Lutzomyia longipalpis与其传播的脊椎动物病毒的互作研究,发现Toll、IMD信号通路、细胞自噬及小RNA干扰(small interfering RNA,siRNA)通路等可能与昆虫对弹状病毒的免疫反应相关。昆虫是弹状病毒主要的寄主和媒介,也是病毒遗传多样性的储主,因此更好地研究和了解昆虫寄主与弹状病毒的相互关系,有助于病毒致病和传播机制以及昆虫抗病毒免疫机理的深入研究。     

New experimental hosts of Barley yellow dwarf virus among wild grasses,with implications for grassland habitats

Barley yellow dwarf virus (BYDV), an economically important virus, infects small grain cereal crops and over 150 other Poaceae species. BYDV infection plays an important role in competition among grasses in non‐managed systems, but many grasses remain unexamined as potential BYDV hosts. This study examined grass species that have not been reported as BYDV hosts but are commonly encountered in non‐managed grasslands throughout the United States and Canada. Laboratory inoculations with BYDV‐PAV using the aphid vector Rhopalosiphum padi were performed to examine the ability of 13 grass species and barley to be infected with the virus; eight of the grass species were not documented previously as virus hosts. Serological and molecular assays were used to confirm BYDV‐PAV infection. Plant height, number of leaves, number of tillers and weight were recorded to evaluate susceptibility or sensitivity to BYDV. Infection with BYDV was experimentally achieved for the first time on Achnatherum lettermanii, Achnatherum occidentale, Achnatherum thurberianum, Danthonia intermedia, Poa fendleriana, Sporobolus airoides and Sporobolus cryptandrus, but not on Alopecurus pratensis and Elymus wawawaiensis. Infection was confirmed in Bromus inermis, Elymus elymoides, Poa bulbosa, Poa secunda and Hordeum vulgare, which served as controls. BYDV infection caused reductions in plant height on P. bulbosa and P. fendleriana. BYDV‐infected P. secunda had more leaves per plant compared to healthy plants of the same species. BYDV‐infected A. lettermanii exhibited reduced dry weight in both below‐ground and above‐ground tissue. These findings have implications for the management and conservation of grassland habitats.     

Mycelial compatibility groups and pathogenic diversity in Sclerotium rolfsii populations from sugar beet crops in Mediterranean‐type climate regions

The population structure of Sclerotium rolfsii from autumn‐sown sugar beet crops in Mediterranean‐type climate regions of Chile, Italy, Portugal and Spain was determined by analyses of mycelial compatibility groups (MCGs) and pathogenicity to 11 economically important plant species. Twelve MCGs (i–xii) were identified among 459 S. rolfsii isolates. MCG iii was the most prevalent group in all countries except Italy. MCG i, the most abundant group (64·7% of isolates) was identified in Portugal and Spain. The remaining MCGs were restricted to various regions within one country (ii, vi, ix) or different countries (v), or to specific localities (iv, vii, viii, x, xi, xii). MCGs iv, vii and x each comprised one isolate. Fields extensively sampled in southern Spain were infected with one to three MCGs. Plant species differed in susceptibility to MCG tester isolates with a MCG by species interaction. Cluster analyses allowed selection into five MCG groupings and grouped plant species into species‐groups 1 (broccoli, chickpea, sunflower, tomato) and 2 (cotton, pepper, sugar beet, watermelon). MCG groupings 1 (i, ix), 2 (ii, iii, vi, viii) and 5 (x, xii) were moderately virulent to species‐group 1 and mildly virulent to species‐group 2. MCG groupings 3 (iv, v, xi) and 4 (vii) were mildly virulent to both species‐groups. Across MCG groups, species were rated highly susceptible (chickpea, sunflower), susceptible (cotton, pepper, tomato, watermelon), moderately resistant (broccoli, melon, sugar beet) and resistant (corn, wheat). Establishing the MCG population structure and virulence variability among S. rolfsii isolates should help in the management of sclerotium root rot diseases.     

ICTV最新十五级分类阶元病毒分类系统中的植物病毒

本文报告了国际病毒分类委员会(ICTV)于2020年3月批准的最新2019病毒分类系统,全面采用了十五级分类阶元,分别为:域、亚域、界、亚界、门、亚门、纲、亚纲、目、亚目、科、亚科、属、亚属、种.寄主为植物的病毒包括了植物病毒和亚病毒感染因子(类病毒、卫星病毒和卫星核酸).植物病毒共有1 608种,涉及2个域、3个界、...     

Molecular characterization and diagnostics of stubby root and virus vector nematodes of the family Trichodoridae (Nematoda: Triplonchida) using ribosomal RNA genes

Plant parasitic nematodes of the family Trichodoridae cause substantial yield losses in many agricultural crops. Rapid and accurate identification of trichodorids to the species level is critical for selection of appropriate measures for control. This study analysed 99 sequences of the D2–D3 expansion segments of the 28S rRNA gene and 131 sequences of the 18S rRNA gene from the stubby nematodes belonging to the genera Nanidorus, Paratrichodorus and Trichodorus. Species delimiting was based on the integration of morphological identification, which is not provided in the present article, and molecular‐based phylogenetic inference and sequence analysis. Twenty‐two valid species and several species complexes were identified among nematodes included in the analysis. PCR‐RFLPs of the partial 18S rDNA and the D2–D3 expansion segments of the 28S rDNA were tested and proposed for identification of these nematodes. Gel PCR‐RFLP profiles and tables with restriction fragment lengths for several diagnostic enzymes are provided for identification. Some problems of taxonomy and phylogeny of nematodes of the family Trichodoridae are also discussed.     

Development of a real‐time PCR method for the detection of the dagger nematodes Xiphinema index,X. diversicaudatum,X. vuittenezi and X. italiae,and for the quantification of X. index numbers

The ectoparasitic dagger nematodes Xiphinema index and Xiphinema diversicaudatum, often at low numbers in the soil, are vectors of grapevine nepoviruses, which cause huge agronomical problems for the vineyard industry. This study reports a method, based on real‐time PCR, for the specific detection of these species and of the closely related non‐vector species Xiphinema vuittenezi and Xiphinema italiae. Specific primers and TaqMan probes were designed from the ribosomal DNA internal transcribed spacer 1 (ITS1), enabling the specific detection of single individuals of each of the X. index, X. diversicaudatum, X. italiae and X. vuittenezi species whatever the nematode population. The specificity of detection and absence of false positive reaction were confirmed in samples of each species mixed with the three other Xiphinema species or mixed with nematodes representative from other genera (non‐plant‐parasitic Dorylaimida, Longidorus sp., Meloidogyne spp., Globodera spp. and Pratylenchus sp.). The method was shown to be valid for the relative quantification of X. index numbers through its use, from crude nematode extracts of soil samples, in a greenhouse assay of grapevine accessions ranging from highly susceptible to resistant. As an alternative to time‐consuming microscopic identification and counting, this real‐time PCR method will provide a fast, sensitive and reliable diagnostic and relative quantification technique for X. index nematodes extracted from fields or controlled conditions.     

Plant community diversity influences vector behaviour and Barley yellow dwarf virus population structure

The species composition of a plant community can affect the distribution and abundance of other organisms including plant pathogens. The goal of this study was to understand the role of host diversity in the transmission of two Barley yellow dwarf virus (BYDV) species that share insect vectors and hosts. Greenhouse experiments measured the transmission rate of BYDV species PAV and PAS from infected oat plants to healthy agricultural and wild grasses and from these species back to healthy oat seedlings. In the field component of the study, the rate of spread of PAV and PAS was measured in monoculture plots planted with agricultural grasses. In greenhouse experiments, the aphid vector more readily transmitted PAV from agricultural grasses and more readily inoculated PAS to the wild grass species assayed. In the field experiment, disease prevalence was greater in wheat, but there was no difference in the rate of spread of PAV and PAS. These results indicate an interaction between vector and host genotype that selects for greater PAV transmission in grain crops, contributes to differences in disease prevalence between grass types, and maintains pathogen diversity within the larger plant community (i.e. agricultural and non‐agricultural hosts).     

PM 8/4 (1) Castanea

Specific scope

The purpose of the EPPO Standard on Castanea is to recommend to EPPO Member Governments the phytosanitary measures which they should use or require for Castanea plants and plant products moving in international trade to prevent the introduction and spread of quarantine pests. Some of these recommendations are addressed to all EPPO Member Governments, others are addressed only to countries considered to face a certain level of risk from the introduction and spread of the regulated pests concerned. All these recommendations were derived from:

• EPPO Standards PM 1/2 (EPPO A1 and A2 Lists) and the former EPPO Standards PM 2 (pest‐specific phytosanitary measures), or
• Pest Risk Analysis (PRA) carried out or reviewed by EPPO, or
• the Working Party on Phytosanitary Regulations.

For wood packaging material, recommendations are based on ISPM 15 Regulation of wood packaging material in international trade.

Specific approval and amendment

First approved in 2010‐09 as PM 8/3 Quercus and Castanea. Revised and approved as a separate Standard PM 8/4 in 2017‐09     

Molecular characterization,comparison of screening methods,and evaluation of cross‐pathogenicity of black rot (Xanthomonas campestris pv. campestris) strains from cabbage,choy sum,leafy mustard and pak choi from Taiwan

Choy sum (Brassica rapa var. parachinensis), leafy mustard (Brassica juncea) and pak choi (B. rapa var. chinensis) are highly nutritious components of diets in Taiwan and other Asian countries, and bacterial black rot caused by Xanthomonas campestris pv. campestris (Xcc) is a major biotic constraint in these crops. As very little was known about the Xcc strains from these crops in these regions, including their cross‐pathogenicity and aggressiveness on different hosts, Xcc strains were obtained from cabbage (Brassica oleracea var. capitata), choy sum, leafy mustard and pak choi crops in Taiwan. Two previously published PCR‐based assays reliably distinguished the Xcc strains from other Xanthomonas species and subspecies. Phylogenetic analysis based on repetitive sequence‐based PCR assays placed the Xcc strains in a clade distinct from other Xanthomonas species, and also showed host specificity. Although all of the Xcc strains from the different host species were pathogenic on all five Brassica test species in both a detached leaf assay and an intact plant assay, in the intact plant assay they showed differences in virulence or aggression on the different test hosts. The Xcc strains from leafy mustard and pak choi were consistently highly aggressive on all the test host genotypes, but the strains from choy sum and cabbage were less aggressive on leafy mustard and choy sum. The intact plant assay proved more discriminating and reliable than the detached leaf assay for comparing the aggressiveness of Xcc strains on different host genotypes, and so, with the new Xcc strains isolated in this study, will be useful for screening leafy brassica germplasm accessions for resistance to black rot.