Strains Of Turnip Mosaic Virus Research Articles

High-throughput RNA sequencing and genetic structure studies of turnip mosaic virus infecting black and yellow mustard revealing emergence of world-B3 pathotype in India.

To study the evolution and host expansion of a TuMV for the first time in India using molecular population genetic framework. Here, we decipher the complete genome sequences of two TuMV world-B3 strains infecting yellow and black mustard in India through high-throughput RNA sequencing subjecting ribosomal RNA depleted mRNA isolated from leaves exhibiting puckering and mosaic symptoms with 100% incidence and high severity in the experimental field. The viral genomes of the two isolates were 9817 and 9829 nucleotides long. They featured two open reading frames (ORFs), one of which encoded a polyprotein comprised of 3164 amino acids and the other of which encoded a PIPO protein of 62 amino acids. The two TuMV strains from New Delhi region shared identity with the world-B pathotype and subpathotype world B3 showcasing its emergence first time in South Asia. In contrast, other isolates reported previously from South Asia were all Asian-BR pathotypes. According to our knowledge, this is the first instance of TuMV association with black mustard naturally. Their geographical prevalence justifies a lower degree of genetic differentiation and higher rate of gene flow calculated between the world-B and Asian-BR pathotypes. This study provides insights on population structuring, expansions and evolution, level of genetic heterogeneity and variability of worldwide prevalent isolates of TuMV which will further aid in understanding virus epidemiology and help prevent losses.

Association between flower stalk elongation, an Arabidopsis developmental trait, and the subcellular location and movement dynamics of the nonstructural protein P3 of Turnip mosaic virus.

Virus infections affect plant developmental traits but this aspect of the interaction has not been extensively studied so far. Two strains of Turnip mosaic virus differentially affect Arabidopsis development, especially flower stalk elongation, which allowed phenotypical, cellular, and molecular characterization of the viral determinant, the P3 protein. Transiently expressed wild‐type green fluorescent protein‐tagged P3 proteins of both strains and selected mutants of them revealed important differences in their behaviour as endoplasmic reticulum (ER)‐associated peripheral proteins flowing along the reticulum, forming punctate accumulations. Three‐dimensional (3D) model structures of all expressed P3 proteins were computationally constructed through I‐TASSER protein structure predictions, which were used to compute protein surfaces and map electrostatic potentials to characterize the effect of amino acid changes on features related to protein interactions and to phenotypical and subcellular results. The amino acid at position 279 was the main determinant affecting stalk development. It also determined the speed of ER‐flow of the expressed proteins and their final location. A marked change in the protein surface electrostatic potential correlated with changes in subcellular location. One single amino acid in the P3 viral protein determines all the analysed differential characteristics between strains differentially affecting flower stalk development. A model proposing a role of the protein in the intracellular movement of the viral replication complex, in association with the viral 6K2 protein, is proposed. The type of association between both viral proteins could differ between the strains.

Biological and Molecular Properties of a Turnip mosaic virus (TuMV) Strain that Breaks TuMV Resistances in Brassica napus.

A new resistance-breaking strain of Turnip mosaic virus (TuMV) overcomes TuMV resistance genes that currently suppress spread of this virus in Brassica napus crops in the Liverpool Plains region of eastern Australia. Isolates 12.1 and 12.5 of this strain and three other isolates in TuMV pathotypes 1 (NSW-2), 7 (NSW-1), and 8 (WA-Ap1) were inoculated to plants of 19 B. napus cultivars and one breeding line. All plants of these cultivars and the breeding line proved susceptible to 12.1 and 12.5 but developed only resistance phenotypes with WA-Ap1 or mostly resistance phenotypes with NSW-1 and NSW-2. Five different TuMV resistance phenotypes occurred either alone or segregating in different combinations. When these five isolates were inoculated to plants of nine other crop or wild Brassicaceae spp. and four indicator hosts in other families, 12.1 and 12.5 resembled the other three in inducing TuMV resistance phenotypes in some Brassicaceae spp. but not others, and by inducing extreme resistance phenotypes in all inoculated plants of B. oleracea var. botrytis and Raphanus sativus. Therefore, the overall resistance-breaking properties of 12.1 and 12.5 were restricted to B. napus. When isolates 12.1, 12.5, and WA-Ap1 and additional Australian isolate WA-EP1 were sequenced and complete genomes of each compared, 12.1 and 12.5 grouped separately from the other 2 and from all 23 Australian isolates with complete genomes sequenced previously. In addition, there was evidence for at least six separate TuMV introductions to Australia. Spread of this B. napus resistance-breaking strain poses a significant threat to the B. napus oilseed industry. Breeding B. napus cultivars with resistance to this strain constitutes a critical priority for B. napus breeding programs in Australia and elsewhere.

An infectious cDNA clone of a radish-infecting Turnip mosaic virus strain

Turnip Mosaic Virus (TuMV) is an economically important potyvirus for which hundreds of hosts have been reported, thus making it a rather exceptional case in the genus. Several viral infectious clones have been generated over the years, which have been useful in deciphering the viral elements involved in the interactions of this virus with the host plant, such as different forms of resistance, gene silencing suppression, host range or host developmental alterations. However, all infectious clones obtained so far correspond to viral isolates within the same phylogenetic cluster, a circumstance biasing our understanding of the peculiarities of this potyvirus. In particular, members of one viral cluster of radish-infecting isolates have been especially reluctant to be copied into infectious clones. This paper reports the construction of an infectious clone of the TuMV isolate JPN 1, belonging to this cluster. The infectious clone maintains all the distinctive biological properties previously described for this viral isolate. The availability of this infectious clone opens the door to many additional studies on the virus, which should allow a deeper understanding of the differential responses to different strains of TuMV in several different hosts.

First Report of White clover mosaic virus and Turnip mosaic virus Mixed Infection on Garlic Mustard in Pennsylvania

HomePlant DiseaseVol. 100, No. 4First Report of White clover mosaic virus and Turnip mosaic virus Mixed Infection on Garlic Mustard in Pennsylvania PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of White clover mosaic virus and Turnip mosaic virus Mixed Infection on Garlic Mustard in PennsylvaniaK. Zhao, P. Margaria, and C. RosaK. ZhaoSearch for more papers by this author, P. MargariaSearch for more papers by this author, and C. RosaSearch for more papers by this authorAffiliationsAuthors and Affiliations K. Zhao P. Margaria C. Rosa , Pennsylvania State University, University Park, PA 16802. Published Online:10 Feb 2016https://doi.org/10.1094/PDIS-09-15-1083-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In spring 2015, 12 weedy garlic mustard (Alliaria petiolata) plants with mosaic symptoms were found in a garden in State College, PA. The same symptoms are seen on many weedy garlic mustards in the area each spring, as they were in previous years at this location. Incidence was ∼10% in the garden, with 2 of ∼20 groups of 4 to 6 plants infected. Quality of RNA extracted from garlic mustard was poor, so symptomatic leaves were used for mechanical transmission to Nicotiana benthamiana. Seven days after mechanical inoculation, plants showed necrotic spots and leaf deformation on the systemic leaves. Double-stranded RNA was extracted from symptomatic N. benthamiana leaves and electrophoresis was performed on 6% polyacrylamide gel to detect dsRNA, produced in plants infected with RNA viruses (Valverde et al. 1990). A band of high molecular weight confirmed the presence of dsRNA. Total RNA was then extracted from the N. benthamiana plants using Spectrum Plant Total RNA Kit (Sigma-Aldrich). A tobravirus or a potyvirus were suspected as possible causal agents, based on literature search for the potyvirus and on the presence a tobravirus infected ornamental plant in the same garden. Two pairs of degenerate primers (Chen et al. 2001; Jones et al. 2008) were used separately in one tube reverse-transcription PCR (RT-PCR) and 835-bp and 654-bp amplicons were cloned into pGEM-T Easy Vector (Promega) and sequenced by Sanger sequencing. The sequences were deposited as GenBank Accession Nos. KT799530 and KT799528, respectively. BLAST results showed that the first sequence had 96% nucleotide identity with the RNA dependent RNA polymerase (RdRp) of a previously reported White clover mosaic virus (WClMV) sequence (AB669182). The second sequence had 95% nucleotide identity to a Turnip mosaic virus (TuMV) sequence across the NIb and coat protein genes (AB252117). Two newly designed primer pairs W_1F (5′-CAGAACGAGCCATCCGCAGAA), W_1500R (5′-TCAGTGCAGTCAGCATTATGAG) and TuMV_F (5′-TCTTGGACGAAGCATGGAGC), TuMV_R (5′-TCGGACTGCCTCTTTGCCTG) were used to further confirm the presence in N. benthamiana of WClMV and TuMV, respectively. A 1,457-bp amplicon was obtained by using W_1F and W_1500R and sequenced. This sequence (KT799531) had 95 to 96% nucleotide identity with several WClMV RdRp sequences (AB056720, AB669182, and X16636). A 577-bp amplicon was obtained by using the primer pair specific to TuMV sequence. The sequenced amplicon (KT788529) showed 97% nucleotide identity to a TuMV sequence spanning the P3 and 6K1 protein (AB701705). Due to the poor quality of RNA we could not test the original or other garlic mustard plants for the presence of the two viruses, but all weeds had uniform symptoms appearance and severity. To our knowledge, White clover mosaic virus and Turnip mosaic virus have not been previously reported in garlic mustard plants in Pennsylvania. Other potyviruses including TuMV have been reported in garlic mustard and Brassicaceae while WClMV to our knowledge was never reported in Brassicaceae or in garlic mustard before. TuMV is a member of the Potyviridae family, is transmitted by aphids in a nonpersistent manner, and causes a variety of symptoms in many Brassica spp.(Tomlinson and Ward 1978) The presence on garlic mustard of a strain of TuMV very similar to a strain already reported in Europe on arugula (Eruca or Brassica vesicaria subsp. sativa) could indicate that this virus can be transmitted between cultivated and not cultivated Brassicaceae and that wild Brassicaceae can potentially serve as virus reservoir (Lockhart 2012). The mode of transmission of WClMV is not known and reports of its transmission by contact or by dodder (Cuscuta spp.) (probably under experimental conditions) have been controversial; therefore, it is hard to speculate if this virus can move from crops to natural environment and vice versa. This is the first report of infection of garlic mustard with TuMV and WClMV, which have the potential to reduce the fitness of this plant species that is considered invasive in North America.

Viral Strain-Specific Differential Alterations in Arabidopsis Developmental Patterns.

Turnip mosaic virus (TuMV) infections affect many Arabidopsis developmental traits. This paper analyzes, at different levels, the development-related differential alterations induced by different strains of TuMV, represented by isolates UK 1 and JPN 1. The genomic sequence of JPN 1 TuMV isolate revealed highest divergence in the P1 and P3 viral cistrons, upon comparison with the UK 1 sequence. Infectious viral chimeras covering the whole viral genome uncovered the P3 cistron as a major viral determinant of development alterations, excluding the involvement of the PIPO open reading frame. However, constitutive transgenic expression of P3 in Arabidopsis did not induce developmental alterations nor modulate the strong effects induced by the transgenic RNA silencing suppressor HC-Pro from either strain. This highlights the importance of studying viral determinants within the context of actual viral infections. Transcriptomic and interactomic analyses at different stages of plant development revealed large differences in the number of genes affected by the different infections at medium infection times but no significant differences at very early times. Biological functions affected by UK 1 (the most severe strain) included mainly stress response and transport. Most cellular components affected cell-wall transport or metabolism. Hubs in the interactome were affected upon infection.

Genetic analyses of the FRNK motif function of Turnip mosaic virus uncover multiple and potentially interactive pathways of cross-protection.

Cross-protection triggered by a mild strain of virus acts as a prophylaxis to prevent subsequent infections by related viruses in plants; however, the underling mechanisms are not fully understood. Through mutagenesis, we isolated a mutant strain of Turnip mosaic virus (TuMV), named Tu-GK, that contains an Arg182Lys substitution in helper component-proteinase (HC-Pro(K)) that confers complete cross-protection against infection by a severe strain of TuMV in Nicotiana benthamiana, Arabidopsis thaliana Col-0, and the Arabidopsis dcl2-4/dcl4-1 double mutant defective in DICER-like ribonuclease (DCL)2/DCL4-mediated silencing. Our analyses showed that HC-Pro(K) loses the ability to interfere with microRNA pathways, although it retains a partial capability for RNA silencing suppression triggered by DCL. We further showed that Tu-GK infection triggers strong salicylic acid (SA)-dependent and SA-independent innate immunity responses. Our data suggest that DCL2/4-dependent and -independent RNA silencing pathways are involved, and may crosstalk with basal innate immunity pathways, in host defense and in cross-protection.

Turnip mosaic virus: potential for crop losses in the grain belt of New South Wales, Australia

The potential of Turnip mosaic virus (TuMV) to infect and damage cool season crops in the grain belt of New South Wales, Australia, was investigated by serological tests on 24,689 dicot weed, grain, and forage specimens from 1999 to 2007 and infectivity/pathogenicity tests with six isolates. Natural infection by TuMV was common in Brassicaceae weeds. Infected grain crops included mustard (Brassica juncea), field pea (Pisum sativum), chickpea (Cicer arietinum), and coriander (Coriandrum sativum). Forage (turnip, Brassica rapa) was also infected. None of 9,816 canola (Brassica napus, at least 19 cultivars) or 1,967 faba bean (Vicia faba, three cultivars) plants were infected. Six isolates from weeds, mustard, and chickpea were inoculated on a range of weed and crop species including four B. napus pathotype differential lines. Inoculated Brassicaceae weeds, mustard, field pea cv. ‘Cressy Blue’, coriander, Chinese cabbage (B. rapa), and forage turnip (B. rapa) were usually infected. Field pea cv. Dundale and radishes (Raphanus sativus) were infected infrequently. Symptoms were severe in mustard, forage turnip, chickpea, and field pea. The reportedly susceptible canola cv. ‘Outback’ displayed only variable infectivity and mild symptoms for five isolates and no infectivity for one isolate. Faba bean, field pea cv. ‘Excell’, and two B. napus differentials appeared to be non-hosts. The results suggest that TuMV strains naturalised in Brassicaceae weeds in NSW in 1999–2007 could damage mustard, field pea, and forage turnip, but not canola or faba bean. These NSW strains appeared to be distinct from strains that damage canola in Europe, North America, and Asia.

Salicylic Acid Determines Differential Senescence Produced by TwoTurnip mosaic virusStrains Involving Reactive Oxygen Species and Early Transcriptomic Changes

Losses produced by virus diseases depend mostly on symptom severity. Turnip mosaic virus (TuMV) is one of the most damaging and widespread potyvirus infecting members of the family Brassicaceae, including Arabidopsis thaliana. We used JPN1 and UK1 TuMV strains to characterize viral infections regarding symptom development, senescence progression, antioxidant response, reactive oxygen species (ROS) accumulation, and transcriptional profiling. Both isolates, despite accumulating similar viral titers, induced different symptomatology and strong differences in oxidative status. Early differences in several senescence-associated genes linked to the ORE1 and ORS1 regulatory networks as well as persistent divergence in key ROS production and scavenging systems of the plant were detected. However, at a later stage, both strains induced nutrient competition, indicating that senescence rates are influenced by different mechanisms upon viral infections. Analyses of ORE1 and ORS1 levels in infected Brassica juncea plants showed a similar pattern, suggesting a conserved differential response to both strains in Brassicaceae spp. Transcriptional analysis of the ORE1 and ORS1 regulons showed similarities between salicylic acid (SA) response and the early induction triggered by UK1, the most severe strain. By means of SA-defective NahG transgenic plants, we found that differential senescence progression and ROS accumulation between strains rely on an intact SA pathway.

Inheritance and development of EST-SSR marker associated with turnip mosaic virus resistance in Chinese cabbage

Li, Q., Tong, H., Zhang, Z., Zhao, Z. and Song, X. 2011. Inheritance and development of EST-SSR marker associated with turnip mosaic virus resistance in Chinese cabbage. Can. J. Plant Sci. 91: 707–715. Turnip mosaic virus (TuMV) is one of the major pathogens infecting Brassica crops (including Chinese cabbage), and often causes serious reductions in yield and quality. Breeding for resistant cultivars is complicated by the existence of numerous TuMV strains and isolates. The objective of this research was to determine the mode of inheritance and to develop molecular markers associated with TuMV resistance in Chinese cabbage. F1and F2populations were developed from the cross between 71-36-2 (susceptible) and 73 (resistant) lines and mechanically inoculated with TuMV-C4. Inheritance analysis by visual scoring and enzyme-linked immunosorbent assay (ELISA) indicated that resistance to TuMV-C4 in this cross was controlled by one recessive gene. A total of 132 EST-SSR primers were designed from EST sequences available in public databases. Seven primers detected polymorphism between parental genotypes. Marker HCC259 was associated with the TuMV resistance Ph-retr02. The distance between the marker and the TuMV resistance gene retr02 was 3.8 cM. This is the first co-dominant marker linked to the TuMV resistance gene with a distance less than 5.0 cM in Chinese cabbage. This marker was suitable for TuMV-C4 resistance screening in progenies from the cross between lines 73 (resistant) and susceptible line, 71-36-2. The usefulness of this marker was validated in 21 additional resistant and susceptible lines. This marker has the potential to simplify and accelerate breeding Chinese cabbage cultivars resistant to TuMV-C4.

Inheritance and development of EST-SSR marker associated with turnip mosaic virus resistance in Chinese cabbage

Li, Q., Tong, H., Zhang, Z., Zhao, Z. and Song, X. 2011. Inheritance and development of EST-SSR marker associated with turnip mosaic virus resistance in Chinese cabbage. Can. J. Plant Sci. 91: 707-715. Turnip mosaic virus (TuMV) is one of the major pathogens infecting Brassica crops (including Chinese cabbage), and often causes serious reductions in yield and quality. Breeding for resistant cultivars is complicated by the existence of numerous TuMV strains and isolates. The objective of this research was to determine the mode of inheritance and to develop molecular markers associated with TuMV resistance in Chinese cabbage. F1 and F2 populations were developed from the cross between 71-36-2 (susceptible) and 73 (resistant) lines and mechanically inoculated with TuMV-C4. Inheritance analysis by visual scoring and enzyme-linked immunosorbent assay (ELISA) indicated that resistance to TuMV-C4 in this cross was controlled by one recessive gene. A total of 132 EST-SSR primers were designed from EST sequences available in public databases. Seven primers detected polymorphism between parental genotypes. Marker HCC259 was associated with the TuMV resistance Ph-retr02. The distance between the marker and the TuMV resistance gene retr02 was 3.8 cM. This is the first co-dominant marker linked to the TuMV resistance gene with a distance less than 5.0 cM in Chinese cabbage. This marker was suitable for TuMV-C4 resistance screening in progenies from the cross between lines 73 (resistant) and susceptible line, 71-36-2. The usefulness of this marker was validated in 21 additional resistant and susceptible lines. This marker has the potential to simplify and accelerate breeding Chinese cabbage cultivars resistant to TuMV-C4.

Identification and sequence analysis of turnip mosaic virus infection on cruciferous crops in southwest of China

Eleven samples were randomly collected from cruciferous plants with green or yellow mosaic symptoms in different areas of the Sichuan province (southwest China). The virus recovered from all samples was recognized as a possible potyvirus by electron microscope observations (negative staining and ultrathin sections) and identified as Turnip mosaic virus (TuMV) by RT-PCR. The coat protein (CP) gene of these isolates was cloned and sequenced. Sequence comparisons showed that these isolates shared 97-100% identity among themselves at the nucleotide level, whereas the identity level with TuMV strains isolated from other parts of China was 89-99.2%. Phylogenetic analysis of the CP sequences revealed that Sichuan isolates clustered in the world-B group. The results also showed that TuMV is a common pathogen of various cruciferous crops in the Sichuan province.

Fusarium Yellows and Turnip Mosaic Virus Resistance in Brassica rapa and B. juncea

Thirty-seven Brassica rapa L. and B. juncea L. lines from nine subspecies were tested for their reaction to two pathotypes of Fusarium yellows (Fusarium oxysporum Schlecht. f. sp. conglutinans (Wr.) Snyd. & Hans. race 1 and F.o. f. sp. raphani Kend. & Snyd. A subset of 16 lines from these same vegetable types were tested for their reaction to four strains of turnip mosaic virus (TuMV-C1, C2, C3, and C4). Resistance to both Fusarium pathotypes was widespread in these Brassica subspecies, whereas resistance to any strain of TuMV was uncommon. The broad availability of resistance to Fusarium yellows and scarcity of resistance to TuMV necessitate different approaches to obtain disease-resistant cultivars.

A viral disease of broad bean caused by a non-aphid-transmissible strain of turnip mosaic virus

A viral disease of broad bean (Vicia faba) was observed in Jiangsu, Zhejiang and Sichuan Province, the People's Republic of China. Its typical symptom on infected leaves was a white mottle, and, rarely, red necrotic lesions on several broad bean cultivars. A non-aphid-transmissible strain of turnip mosaic virus (TuMV) was identified as the causal agent of the disease on the basis of biological properties, particle morphology, seed and aphid transmission and serological tests. The virus could not be transmitted by aphids in the non-persistent manner.

Genetics of resistance to five strains of turnip mosaic virus in Chinese cabbage

Inheritance of resistance to turnip mosaic virus (TuMV) strains C1, C2, C3, C4, and C5 in Chinese cabbage (Brassica campestris subsp. pekinensis) was evaluated using monoclonal antibodies. Crosses were made between a resistant line, ‘0–2’, and four susceptible line. ‘Seoul’ (SE),‘SSD31’ (SS), ‘Cheongbang’ (CH), and ‘Yaki 1 ho’ (YA), to determine the inheritance of resistance of ‘0–2’ in different genetic backgrounds. Resistance to TuMV was controlled by a single dominant gene or double dominant genes depending on the strain and cross. The resistance genes of ‘0–2’ were modified by susceptible parents such that a single dominant gene was involved in the ‘SS×0–2’ combination, but double dominant genes in the ‘SE×0–2’ against TuMV-C3 or TuMV-C5. ELISA tests using inoculated and noninoculated leaves in the same plant suggested that the dominant resistance genes inhibit virus movement rather than virus multiplication.

Biological, Serological and Coat Protein Properties of a Strain of Turnip Mosaic Virus Causing a Mosaic Disease of Brassica campestris and B. juncea in India

Biological, serological and coat protein properties of a potyvirus (Poty‐Rape) causing a mosaic disease of Brassica campestris and B. juncea in India were investigated. The virus readily infected 4 of the 5 plant species in the family Brassicaceae in which it induced severe systemic mosaic symptoms; it also induced chlorotic and necrotic local lesions in Chenopodium amaranticolor, but failed to infect 4 other species of Chenopodiaceae or 20 species of Amaranthaceae, Apiaceae, Canabinaceae, Compositae, Cucurbitaceae, Euphorbiaceae, Leguminosae and Solanaceae. The virus was transmitted in a non‐persistant manner by Myzus persicae, Brevicoryne brassicae and Aphis gossypii. The Average size, of the virus particles in a purified preparation was 740 nm × 12 nm. SDS‐PAGE analysis of the viral coat protein showed two major bands of approximately 37 kDa and 31 kDa, a pattern very similar to that of a reference isolate of turnip mosaic virus (TuMV) from the U.S. In Western‐blot immunoassay, an antiserum to TuMV reacted with both the coat protein bands of the Poty‐Rape islate and the reference TuMV, but not with the coat proteins of four other potyviruses. The high performance liquid chromatographic profile of tryptic peptides from the coat protein of Poty‐Rape was found to be very similar to that of the reference TuMV, but differed substantially from those of four other potyviruses. The Poty‐Rape isolate is considered to be a distinct strain of, TuMV.

Characterization of epitopes recognized by monoclonal antibodies to aphid transmissible and non-transmissible strains of turnip mosaic virus.

Fourteen monoclonal antibodies (MAbs) were prepared against two strains of turnip mosaic virus (TuMV) differing in aphid transmissibility. Serological specificity of fourteen MAbs against the two strains was tested by indirect ELISA. Three MAbs were able to distinguish aphid transmissible TuMV strain 1 from non-aphid transmissible strain 31 while four MAbs reacted only with strain 31. No cross-reactivity between the two strains was found using these specific MAbs. Based upon the ability of Mab to inhibit the reaction of other MAbs, antibody competition test indicated that fourteen MAbs recognized six different epitopes on the virus particle; MAbs specific to strain 1 recognized two epitopes while MAbs specific to strain 31 also recognized two epitopes. The remaining two epitopes are common. Since the six amino acid differences between the coat proteins of the two strains were found at the N-terminal regions, MAbs specific to strain 1 or 31 bound to the different epitopes on the N-terminal regions in coat proteins of the two strains.

Turnip Mosaic Virus Strains in Southern Ontario, Canada

Turnip Mosaic Virus Strains in Southern Ontario, Canada

Reactions of white cabbage (Brassica oleracea var. capitata) to four different strains of turnip mosaic virus

SUMMARYTuMV strains isolated in the UK, Germany, Denmark and Greece have been shown to be biologically distinct by host range studies. The effects of the four strains on symptoms, yield and storage performance of four cultivars of white cabbage were assessed in gauze house experiments. Three of the cultivars, Decema Extra, Vitala and Winter White III, were known to have high levels of resistance to the UK strain and the fourth, cv. Polinius, is known to be highly susceptible. The resistance to the UK strain previously observed in the three ‘resistant cultivars’ was generally effective against the other three strains; however, the level of resistance was virus strain dependent and variable for the symptoms of external necrosis, internal necrosis and yield depression. The UK strain caused the highest level of external necrosis and the German strain the highest internal necrosis. These two strains generally caused greater yield reductions than the Danish or Greek strains. Virus infection had no effect upon the incidence of the pepper‐spot necrosis disorder. Breeding strategies for handling the observed resistance are discussed.

Cell-free Translation of Turnip Mosaic Virus RNA

Summary RNA from the type strain of turnip mosaic virus (TuMV), a member of the poty virus group, was translated in vitro in either rabbit reticulocyte lysate or wheat germ extract. We found no evidence for encapsidated, subgenomic TuMV RNA species. A broad size range of l-[3SS]methionine-labelled polypeptides with molecular weights up to 200000 (200K) was observed in TuMV RNA-programmed reticulocyte lysates. In contrast, a single polypeptide of 44K predominated in the much narrower spectrum of labelled products, of 55K or less, seen in wheat germ extracts containing TuMV RNA. Time course experiments revealed that, in rabbit reticulocyte incubations, many of the low molecular weight TuMV RNA-encoded polypeptides accumulated only after synthesis of the largest polypeptides (i.e. those ⩾100K). When the amino acid analogues p-fluorophenylalanine, l-canavanine and N-tosyl-lysyl-chloromethane were substituted for phenylalanine, arginine and lysine respectively, the major 44K product detected in wheat germ extracts diminished, to be replaced by a product of 92K which co-migrated with the major polypeptide normally observed in reticulocyte incubations. A rapid processing event may occur in standard wheat germ incubations to release the 44K polypeptide from a nascent, elongating precursor. The 44K product did not arise because of limiting amounts of a particular tRNA species. Reticulocyte incubations with or without additional reducing agent showed comparable levels of all the processed TuMV RNA-specific products. We could detect no serological crossreaction between any of the TuMV RNA-encoded products and antiserum raised against HPLC-purified helper component of tobacco vein mottling virus, another potyvirus.