Identification of vectors of rice yellow mottle virus in Tanzania

Rice yellow mottle virus (RYMV) is specific to Africa and has been reported in some countries in East Africa and almost all the countries in West Africa. At present, it is undoubtedly the most important disease of rice in Tanzania. It was first reported in the 1980's. It has spread fast and is now found in almost all the rice growing areas. In view of the increasing incidence and importance of RYMV on rice production in Tanzania, studies on the epidemiology of the disease were initiated in order to find ways of controlling the disease. Transmission studies were carried out on seventy‐seven species of beetles and grasshoppers collected from different rice growing locations to determine vector identity. Four vectors have been identified (three chrysomelids; Dactylispa sp., Chaetocnema sp. and Chaetocnema pulla) and one tetrigid grasshopper. The wide distribution of Chaetocnema spp. in the RYMV endemic areas suggests that the species are the most important vectors responsible for infections in these areas.     

Evidence and population diversity of the rice yellow mottle virus (RYMV) insect vectors and some of their natural antagonists in paddy fields in the north of Cameroon

From 2002 to 2004 two sampling methods were combined to assess the population of insects known as vectors of rice yellow mottle virus (RYMV) in the three major irrigated rice ecosystems in the north of Cameroon (Lagdo, Maga, Yagoua) and in lowland rice fields. Samplings were conducted by means of sweep net and D-Vac (the sucking trap) fortnightly in 2002 and 2003 until mid-October in lowland rice fields while in the irrigated fields, samplings occurred between December and April. Simultaneously, rearing on death concerned insects was conducted in the laboratory to identify the parasitoid insect species. From samples obtained at the different sites: (1) the dominant structure of the RYMV insect vectors was analysed according to the rice phenology; (2) the diversity and the occurrence of potential major groups of predators and parasitoids were assessed. Among the RYMV insect vectors sampled: Chaetocnema pulla Chapuis (Coleoptera: Chrysomelidae), Chnootriba similis Mulsant (Coleoptera: Coccinellidae), Trichispa sericea Guerin-Meneville (Coleoptera: Chrysomelidae), Locris rubra Fabricius (Hemiptera: Cicadellidae), Oxya hyla Stål (Orthoptera: Acrididae) and Conocephalus longipennis (de Haan) (Orthoptera: Tettigoniidae) were the most encountered insect species during the rice growing seasons. When investigating the arthropods acting in the rice fields as predators, spiders (Araneae) came at the top position with a high concurrency of Pardosa spp. (>42%) at all sites. At the sites Maga and Yagoua, the carabid beetles species Abacetus crenulatus Dejean and Abacetus foveolatus Chaudoir were the most numerous whereas the Lagdo site was highly colonised by Clivina erythropyga Putzeys, Paederus sabaeus Erichson and Stenus ravus Puthz were the most abundant staphylinid beetles. The rearing of dead RYMV insect vectors gave results on the emergence of the following parasitoids: Eurytoma spp., Pediobius spp., Tetrastichus spp., Telenomus spp.     

云南30个水稻品种对水稻白叶枯病的抗性评价

【目的】水稻白叶枯病是一种严重危害水稻的细菌性病害,培育抗性品种是治理该病害的重要途径。因此,明确云南水稻材料对检疫性病害水稻白叶枯病的抗性,可以为该病害的防治与监测、水稻栽培的合理布局和良好抗性资源的获取提供依据。【方法】采用剪叶接种法测定云南稻区30个品种对7个不同致病型白叶枯病菌的抗性。【结果】在供试的30个云南水稻品种中,2个品种(玉粳16和JS42糯稻)对7个不同致病型菌株均表现为抗性;15个品种对7个致病型菌株均表现感病;对HEN11、SCYC-6、YN7、YN11、FUJ、YN241和PX099等7个致病型菌株表现抗性的水稻品种分别占26.67%、16.67%、23.33%、13.33%、6.67%、10.00%和20.00%。此外,区试材料的抗性比例高于主栽品种,地方稻未发现抗性品种。【结论】现在生产上的大部分水稻品种对优势致病型病原菌入侵的抵抗能力降低甚至丧失。针对云南地区的优势致病小种FUJ筛选得到2个抗性品种:玉粳16和JS42糯稻。     

Ectopic expression of the spike protein of Rice Ragged Stunt Oryzavirus in transgenic rice plants inhibits transmission of the virus to insects

Rice ragged stunt oryzavirus (RRSV) replicates in both its insect vector, Nilaparvata lugens, and its plant host, rice, and has a complex multi-component particle bearing spikes on its outer surface. Transgenic rice lines expressing the 39 kDa spike protein showed good resistance to infection by RRSV. Furthermore, N. lugens fed on these plants prior to feeding on RRSV-infected plants were significantly protected against RRSV infection. The viral titre in insects initially fed on transgenic plants and then on RRSV-infected plants was inversely proportional to the levels of the 39 kDa protein expressed in the transgenic plants. This suggests that the 39 kDa protein interferes with the interaction between the intact virus particles and insect cell receptors and that the spike protein of RRSV contributes to vector specificity. This approach would probably be a more environment-friendly and sustainable method of virus control than by actual eradication of insect vectors.     

Pea aphid biotypes differing in bean yellow mosaic virus transmission

Two pea aphid (Acyrthosiphon pisum (Harris)) biotypes were isolated which differed greatly in efficiency of bean yellow mosaic virus transmission. The two biotypes ranked differently in efficiency of bean yellow mosaic virus transmission among eight other aphid species, including three species not previously reported as vectors of bean yellow mosaic virus. These new vectors are Brachycaudus helichrysi (Kltb.), Cavariella aegopodii (Scop.), and Therioaphis riehmi (Börner). These biotypes also differed consistently in body size and in fecundity on pea cultivars.

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Zusammenfassung Es wùrden 2 Erbsenlaus-Biotypen (Acyrthosiphon pisum (Harris)) isoliert, deren Wirksamkeit als Überträger des Gelbmosaikvirus der Buschbohnen auf Erbsen sehr verschieden ist. Die beiden Biotypen ordnen sich dabei an verschiedene Stellen in einer Reihe von acht anderen Blattlausarten ein, die drei bisher nicht als Vektoren des Bohnenhelbmosaiks nachgewiesene Arten umfaßt. Diese neuen Vektoren sind Brachycaudus helichrysi (Kltb.), Cavariella aegopodii (Scop.) und Therioaphis riehmi (Börner). Die Biotypen unterscheiden sich durchweg auch in Körpergröße und Fruchtbarkeit auf verschiedenen Erbsensorten.

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Approved for publication as technical paper number 1725, Oregon Agricultural Experiment Station.     

Rice Ragged Stunt Oryzavirus: role of the viral spike protein in transmission by the insect vector

A 39 kDa protein, known as the viral spike protein or one of the protein components forming the viral spike, encoded by genomic segment 9 (S9) of Rice Ragged Stunt Oryzavirus (RRSV) was obtained by enzymatic cleavage of a fusion protein expressed by S9 cDNA in bacteria with proteinase factor Xa. The feeding of an insect vector — the rice brown planthopper (Nilaparvata lugens) on purified expressed 39 kDa protein before the inoculation of the insects on diseased rice plants could completely inhibit the vector transmission ability of the insect. The presence of a 32 kDa insect cell membrane protein which could bind to 39 kDa viral spike protein indicated that the inhibition might be resulted from the competition in the interactions of 39 kDa protein and intact virus with the virus receptors on the insect cells. These results suggest that the spike proteins of the plant reoviruses are essential for the virus infection in the interactions of virus, insect vectors and host plants. These results are also useful in the practical applications.     

Genome‐wide association study identifies an NLR gene that confers partial resistance to Magnaporthe oryzae in rice

Because of the frequent breakdown of major resistance (R) genes, identification of new partial R genes against rice blast disease is an important goal of rice breeding. In this study, we used a core collection of the Rice Diversity Panel II (C‐RDP‐II), which contains 584 rice accessions and are genotyped with 700 000 single‐nucleotide polymorphism (SNP) markers. The C‐RDP‐II accessions were inoculated with three blast strains collected from different rice‐growing regions in China. Genome‐wide association study identified 27 loci associated with rice blast resistance (LABRs). Among them, 22 LABRs were not associated with any known blast R genes or QTLs. Interestingly, a nucleotide‐binding site leucine‐rich repeat (NLR) gene cluster exists in the LABR12 region on chromosome 4. One of the NLR genes is highly conserved in multiple partially resistant rice cultivars, and its expression is significantly up‐regulated at the early stages of rice blast infection. Knockout of this gene via CRISPR‐Cas9 in transgenic plants partially reduced blast resistance to four blast strains. The identification of this new non‐strain specific partial R gene, tentatively named rice blast Partial Resistance gene 1 (PiPR1), provides genetic material that will be useful for understanding the partial resistance mechanism and for breeding durably resistant cultivars against blast disease of rice.     

Transgenic rice expressing <Emphasis Type="Italic">Allium sativum</Emphasis>leaf agglutinin (ASAL) exhibits high-level resistance against major sap-sucking pests

Background  

Rice (Oryza sativa) productivity is adversely impacted by numerous biotic and abiotic factors. An approximate 52% of the global production of rice is lost annually owing to the damage caused by biotic factors, of which ~21% is attributed to the attack of insect pests. In this paper we report the isolation, cloning and characterization of Allium sativum leaf agglutinin (asal) gene, and its expression in elite indica rice cultivars using Agrobacterium-mediated genetic transformation method. The stable transgenic lines, expressing ASAL, showed explicit resistance against major sap-sucking pests.     

Influence of soil factors and cultural practice on biological control of sheath blight of rice with antagonistic bacteria

Fluorescent and nonfluorescent strains of bacteria isolated from rice rhizospheres on the International Rice Research Institute (IRRI) farm were evaluated for in vitro antibiosis towards the sheath blight (ShB) pathogen Rhizoctonia solani, and for suppression of ShB in detached rice leaves. Efficient strains were located on the basis of consistent performance in two laboratory tests. Among nine efficient strains, 3 strains were identified as Pseudomonas fluorescens, 5 strains were tentatively identified as Bacillus spp. and one strain was identified as Enterobacter. In three greenhouse tests lowland rice soils with optimum pH for rice growth (pH 5.5–6.5), acidic pH (pH 5.0) and boron toxicity were found more suitable for biological control of ShB and, less frequently, also yield increases than were alkaline (pH 6.9) and zinc-deficient soils. Bacterial treatments afforded significant ShB reductions in 3 field experiments, but no significant yield increases resulted. In direct-seeded rice best performances by bacterial treatments in terms of ShB suppression were 66 and 98% during DS 1988 and WS 1988, respectively, which were comparable to or better than the performance of validamycin (a fungicide routinely used for ShB control) which afforded 42 and 63% disease suppression, respectively, in the same experiments. Although bacterial treatments caused ShB reductions both in direct-seeded and transplanted rice crops, disease control was more pronounced in direct-seeded than in transplanted crops. These results indicate that carefully selected strains of bacterial antagonists have the potential for ShB suppression in rice at least in areas where direct-seeding is practised.     

Laodelphax striatellus Atg8 facilitates Rice stripe virus infection in an autophagy-independent manner

Rice stripe virus(RSV)is the causative agent of rice stripe disease and is completely dependent on insect vectors for its plant-to-plant transmission.Laodelphax striatellus is the major insect vector for RSV.In this study,we explored the interactions be-tween RSV infection and L.striatellus autophagy,a potential intrinsic antiviral mechanism in insects.We found that L.striatellus autophagic activity did not affect RSV infection;however,the autophagy related-8(Atg8)gene significantly enhanced virus infection.Dur-ing RSV initial infection within the L.striatellus midgut,silencing of Atg8 expression significantly decreased the phosphorylation of c-Jun N-terminal kinase(p-JNK);however,when RSV infection is absent,silencing of Atg8 did not alter p-JNK levels.Thesc results indicated that Atg8 might activate the JNK machinery by allowing more virus infection into cells.We further revealed that Atg8-deficiency significantly decreased RSV accumu-lation on the surface of the insect midgut epithelial cells,suggesting a receptor trafficking function of the y-aminobutyric acid receptor-associated protein family.Using the RSV ovary entry as a model,in which vitellogenin receptor(V gR)mediates RSV cell entry,we clarified that Atg8-deficiency decreased the abundance of V gR localizing on the cytomem-brane and disturbed the attachment of RSV in the germarium zones.Collectively,these results revealed an autophagy-independent function of L.striatellus Atg8 that enhances RSV initial infection by increasing virus attachment on the infection sites.     

Genotypic and Pathotypic Diversity of Xanthomonas oryzae pv. oryzae Strains in Taiwan

Rice bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae [(Ishiyama) Swings et al. 1990] (Xoo), is a major rice disease of the second crop season in Taiwan. A total of 88 Xoo strains collected from 10 major rice cultivating areas in Taiwan from 1986, 1997, 2000, 2004, and 2011 were characterized by repetitive‐element PCR (REP‐PCR) fingerprinting and virulence analyses. Among the five genetic clusters identified by the pJEL1/pJEL2 (IS1112‐based) and REP1R‐Dt/REP2‐D [repetitive extragenic palindromic (REP)‐based] primer sets, clusters A, C and D contained Xoo strains from geographically distant regions, which suggests a high frequency of Xoo dispersal in Taiwan. The 88 Xoo strains were evaluated by inoculations on IRBB near‐isogenic lines and five Taiwan rice cultivars. A subset of 45 moderately or highly virulent strains were classified into 15 pathotypes by their compatible or incompatible reactions on IR24 and 12 IRBB near‐isogenic lines, each containing a single resistance gene. Analysis of molecular haplotypes and pathotypes revealed a partial relationship. IRBB5, IRBB21 and IRBB4 were incompatible with 96%, 96% and 73% of the strains, so xa5, Xa21 and Xa4 can recognize most of the Xoo strains in Taiwan and elicit resistance. In contrast, IRBB3 (Xa3), IRBB8 (xa8), IRBB10 (Xa10), IRBB11 (Xa11), IRBB13 (xa13) and IRBB14 (Xa14) were susceptible to almost all of the 45 Xoo strains. Inoculation trials revealed significant differences in the susceptibility of five Taiwan cultivars to Xoo (from high to low susceptibility: Taichung Sen 10 >  IR24, Taichung Native 1 >  Taichung 192, Taikeng 9, Tainan 11). This study provides useful information for resistance breeding and the development of disease management strategies against bacterial blight disease of rice.     

Isolation and evaluation of the biocontrol potential of Talaromyces spp. against rice sheath blight guided by soil microbiome

Rice sheath blight caused by Rhizoctonia solani is the major disease of rice that seriously threatens food security worldwide. Efficient and eco-friendly biological approaches are urgently needed since no resistant cultivars are available. In this study, fallow and paddy soils were initially subjected to microbiome analyses, and the results showed that Talaromyces spp. were significantly more abundant in the paddy soil, while Trichoderma spp. were more abundant in the fallow soil, suggesting that Talaromyces spp. could live and survive better in the paddy soil. Five Talaromyces isolates, namely, TF-04, TF-03, TF-02, TF-01 and TA-02, were isolated from the paddy soil using sclerotia of R. solani as baits and were further evaluated for their activity against rice sheath blight. These isolates efficiently parasitized the hyphae and rotted the sclerotia even at higher water contents in the sterilized sand and the soil. Isolate TF-04 significantly promoted rice growth, reduced the severity of rice sheath blight and increased the rice yield under outdoor conditions. Defence-related genes were upregulated and enzyme activities were enhanced in rice treated with isolate TF-04. Our research supplies a microbiome-guided approach to screen biological control agents and provides Talaromyces isolates to biologically control rice sheath blight.     

Genetic engineering of rice to resist rice tungro disease

Rice tungro disease (RTD), caused by the co-infection of rice tungro bacilliform virus (RTBV) and rice tungro spherical virus, is one of the most important viral diseases of rice in South and Southeast Asia. The disease remains one of the major threats to sustainable rice production in many countries. The lack of resistance genes to RTBV—the causal agent of tungro disease—makes it even more difficult to manage RTD. In this review, we summarize previous and current research efforts to genetically engineer rice in order to increase the crop’s resistance to tungro disease, including the use of pathogen-derived resistance and of host genes that confer RTD resistance and/or that restrict feeding by the insect vector. The prospects of developing rice cultivars with durable resistance to RTD are also discussed.     

Assessment of mycoflora and infestation of insects,vector of <Emphasis Type="Italic">Aspergillus</Emphasis> section <Emphasis Type="Italic">Flavi</Emphasis>, in stored peanut from Argentina

The occurrence of spoilage fungi and Aspergillus section Flavi populations, the aflatoxins incidence, the role of insects as vectors of mycotoxin-producing fungi and the AFs-producing ability of the isolated species throughout the peanut (Arachis hypogaea L.) storage period were evaluated. Analyses of fungal populations from 95 peanut seed samples did not demonstrate significant differences between the incidences in each sampling period. Aspergillus section Flavi were isolated during all incubation periods. Cryptolestes spp. (Coleoptera: Cucujidae) were collected in August, September and October with 18, 16 and 28% of peanut samples contaminated, respectively. Insects isolated during August showed 69% of Aspergillus section Flavi contamination. A. flavus was the most frequently isolated (79%) from peanut seeds and from insect (59%). The greater levels of AFB₁ were detected in September and October with a mean of 68.86 μg/kg and 69.12 μg/kg respectively. The highest proportion of A. flavus toxigenic strains (87.5%) was obtained in June. The presence of Aspergillus section Flavi and insect vectors of aflatoxigenic fungi presented a potential risk for aflatoxin production during the peanut storage period. Integrated management of fungi and insect vectors is in progress.     

Field inoculation of sorghum and rice withAzospirillum spp. andHerbaspirillum seropedicae

Two field experiments were carried out at the UAPNPBS experimental station, Seropédica, with two sorghum and one rice cultivars. The establishment, and inoculation effects, ofAzospirillum spp. andHerbaspirillum strains marked with antibiotic resistance were investigated. One grain sorghum (BR 300) and one sugar sorghum (Br 505) cultivar were used.Azospirillum lipoferum strain S82 (isolated from surface sterilized roots of sorghum) established in both cultivars and comprised 40 to 80% of theAzospirillum spp. population in roots and stems 60 days after plant emergence (DAE).Azospirillum amazonense strain AmS91 (isolated from surface-sterilized roots of sorghum) reached only 50%. At 90 DAE, S82 almost disappeared (less than 30% of establishment) while the establishment of AmS91 remained constant in roots and stems. No establishment ofH. seropedicae strain H25 (isolated from surface-sterilized roots of sorghum) orA. lipoferum strain S65 (isolated from the root surface of sorghum) could be observed on inoculated roots. Inoculation with S82, AmS91 or S65 but not withH. seropedicae H25, increased plant dry weight of both cultivars and total N in grain of the grain sorghum. In rice,A. lipoferum Al 121 andA. brasilense Sp 245 (isolated from surface sterilized rice and wheat roots respectively) established in the roots but there was no increase inAzospirillum spp. numbers due to inoculation. None of the strains affected plant growth or rice grain yield.Azospirillum amazonense, A82 andH. seropedicae Z95, which did not establish in roots, significantly enhanced seed germination.     

Deciphering the multiplication behaviour of Rice tungro bacilliform virus by absolute quantitation through real-time PCR

Rice tungro virus disease is one of the most destructive diseases that cause extensive damage to the rice crop. To elucidate the multiplication behaviour of Rice tungro bacilliform virus (RTBV), real-time Polymerase chain reaction (PCR) experiments were performed on rice and insect vector green leafhopper (GLH). SYBR green chemistry-based real-time PCR assay for the quantification of RTBV was developed. A standard curve using plasmid DNA was constructed to determine the absolute quantity of RTBV genome copies in different plant tissues and GLH vector. Here, 6.309?×?10⁴, 7.943?×?10⁵, 3.162?×?10⁶ and 3.162?×?10³ RTBV genome copies per ng of total DNA were estimated in root, shoot, leaf and panicles, respectively, on virus-infected rice cultivar TN1. In addition, 5.011?×?10³ copies of virus in an individual GLH were quantified. Also, RTBV was quantified at different time interval after inoculation. The real-time assay was performed with five different RTBV isolates that showed differential accumulation pattern of virus isolates in a same host. These results provide new insight into the biology of the economically important interaction between rice, GLH and RTBV.     

Biochemical defence responses of resistant and susceptible rice genotypes against blast pathogen Magnaporthe oryzae

Abstract

Rice blast is the leading fungal disease which is caused by Magnaporthe oryzae that contributes for the significant decline in the rice yield throughout the globe. There is a need for the understanding of biochemical changes in rice plant during blast infection for the development of novel disease control strategies. In the present study, we isolated M. oryzae from the local paddy fields and the fungal isolates (VCF and PON) were identified by ITS-PCR using genomic DNA samples. Further, we inoculated resistant (BR2655 and TUNGA) and susceptible (INTAN and HR12) rice cultivars with PON and VCF isolates. PON isolate showed relatively high virulence compared to VCF and standard MTCC fungal strains. Therefore, we evaluated the effect of PON on the total protein content and plant defence-related key enzymes (peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, β-glucosidase, chitinase and lipoxygenase) activities between 24- and 120-hour post-inoculation (hpi). The results demonstrated the decrease in total protein content in all the inoculated cultivars. In addition, we observed the variation in the activity of peroxidase, polyphenol oxidase, β-glucosidase, chitinase and lipoxygenase at different time points in all the tested rice plants compared to respective controls. However, no significant difference was observed in the phenylalanine ammonia lyase activity relative to its control. Taken together, this study emphasizes on the variation in the activities of plant defence enzymes in different plant cultivars against the tested fungal pathogen and also implementation of defence enzymes as biochemical markers for resistant breeding.     

Expression of multiple insecticidal genes confers broad resistance against a range of different rice pests

We report the simultaneous introduction of three insecticidal genes (the Bt genes cry1Ac and cry2A, and the snowdrop lectin gene gna) into commercially important indica rice varieties M7 and Basmati 370, by particle bombardment. Transgenic plants expressed Cry1Ac, Cry2A and GNA at different levels, either singly or in combination at 0.03–1%, 0.01–0.5% and 0.01–2.5% of total soluble protein, respectively. The transgenes showed stable transmission and expression, and R₁ transgenic plants provided significant (p<0.01) protection against three of the most important insect pests of rice: rice leaf folder (Cnaphalocrocis medinalis), yellow stemborer (Scirpophaga incertulas) and brown planthopper (Nilaparvata lugens). The triple transformants showed significantly (p<0.05) higher resistance to these insects than plants expressing single transgenes. Bioassays using the triple-transgenic plants showed 100% eradication of the rice leaf folder and yellow stem borer, and 25% reduction in the survival of the brown planthopper. The greatest reduction in insect survival, and the greatest reduction in plant damage, occurred in plants expressing all three transgenes. This approach maximises the utility of gene transfer technology to introduce combinations of genes whose products disrupt different biochemical or physiological processes in the same insect, providing a multi-mechanism defence.     

A novel approach for developing resistance in rice against phloem limited viruses by antagonizing the phloem feeding hemipteran vectors

Rice production is known to be severely affected by virus transmitting rice pests, brown planthopper (BPH) and green leafhopper (GLH) of the order hemiptera, feeding by phloem abstraction. ASAL, a novel lectin from leaves of garlic (Allium sativum) was previously demonstrated to be toxic towards hemipteran pests when administered in artificial diet as well as in ASAL expressing transgenic plants. In this report ASAL was targeted under the control of phloem-specific Agrobacterium rolC and rice sucrose synthase-1 (RSs1) promoters at the insect feeding site into popular rice cultivar, susceptible to hemipteran pests. PCR, Southern blot and C-PRINS analyses of transgenic plants have confirmed stable T-DNA integration and the transgenes were co-segregated among self-fertilized progenies. The T₀ and T₁ plants, harbouring single copy of intact T-DNA expression cassette, exhibit stable expression of ASAL in northern and western blot analyses. ELISA showed that the level of expressed ASAL was as high as 1.01% of total soluble protein. Immunohistofluorescence localization of ASAL depicted the expected expression patterns regulated by each promoter type. In-planta bioassay studies revealed that transgenic ASAL adversely affect survival, growth and population of BPH and GLH. GLH resistant T₁ plants were further evaluated for the incidence of tungro disease, caused by co-infection of GLH vectored Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV), which appeared to be dramatically reduced. The result presented here is the first report of such GLH mediated resistance to infection by RTBV/RTSV in ASAL expressing transgenic rice plant.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .