Beet Necrotic Yellow Vein Virus Research Articles

Suppression of Resistance-Breaking Beet necrotic yellow vein virus Isolates by Beet oak-leaf virus in Sugar Beet.

Rhizomania, a serious disease of sugar beet (Beta vulgaris), is caused by Beet necrotic yellow vein virus (BNYVV). Resistance allele Rz1 has been widely incorporated into commercial cultivars. Recently, resistance-breaking isolates of BNYVV (RB-BNYVV) were identified and characterized. When the occurrence of RB-BNYVV was surveyed throughout the sugar-beet-growing areas in the United States, most soil samples contained Beet oak-leaf virus (BOLV) as well. BNYVV and BOLV often occurred in the same field and sometimes in the same sugar beet plant. The possibility of interactions between these two Polymyxa betae-transmitted sugar beet viruses was tested. Plants grown in soils infested with aviruliferous P. betae or carrying RB-BNYVV and BOLV, alone and in combination, were compared with plants grown in noninfested soil for differences in plant fresh weight and virus content as measured by enzyme-linked immunosorbent assay (ELISA). Rz1 and Rz2 resistance genes that condition resistance to BNYVV did not confer resistance to BOLV. BNYVV ELISA values were significantly higher in single infections than in mixed infections with BOLV in both the rhizomania-resistant and -susceptible cultivars. In contrast, ELISA values of BOLV were not significantly different between single and mixed infections in both the rhizomania-resistant and -susceptible cultivars. Results indicate that BOLV may suppress BNYVV in mixed infections. Soils infested with P. betae significantly reduced fresh weight of sugar beet seedlings regardless of whether they were with or without one or both viruses or resistance genes.

Molecular and serological characterization of an Iranian isolate of Beet black scorch virus

An isolate of Beet black scorch virus (BBSV) was obtained from Iranian sugar beet roots. Its genome organization closely resembles that of the previously described Chinese and North American isolates, but the nucleotide sequences of the three isolates differ considerably. Most of the nucleotide exchanges, however, are silent, and the Iranian and the Chinese isolates were serologically indistinguishable. Beets infected by the Iranian BBSV did not show black scorch symptoms, but severe root beardedness. This might have been caused by BBSV or the simultaneously present beet necrotic yellow vein virus, or both together.

Identification of amino acids of the beet necrotic yellow vein virus p25 protein required for induction of the resistance response in leaves of Beta vulgaris plants

The RNA3-encoded p25 protein of beet necrotic yellow vein virus (BNYVV) is responsible for the production of rhizomania symptoms of sugar beet roots (Beta vulgaris subsp. vulgaris). Here, it was found that the presence of the p25 protein is also associated with the resistance response in rub-inoculated leaves of sugar beet and wild beet (Beta vulgaris subsp. maritima) plants. The resistance phenotype displayed a range of symptoms from no visible lesions to necrotic or greyish lesions at the inoculation site, and only very low levels of virus and viral RNA accumulated. The susceptible phenotype showed large, bright yellow lesions and developed high levels of virus accumulation. In roots after Polymyxa betae vector inoculation, however, no drastic differences in virus and viral RNA accumulation levels were found between plants with susceptible and resistant phenotypes, except at an early stage of infection. There was a genotype-specific interaction between BNYVV strains and two selected wild beet lines (MR1 and MR2) and sugar beet cultivars. Sequence analysis of natural BNYVV isolates and site-directed mutagenesis of the p25 protein revealed that 3 aa residues at positions 68, 70 and 179 are important in determining the resistance phenotype, and that host-genotype specificity is controlled by single amino acid changes at position 68. The mechanism of the occurrence of resistance-breaking BNYVV strains is discussed.

Breeding for Multiple Disease Resistance in Sugarbeet: Registration of FC220 and FC221

FC220 (Reg. No. GP‐263, PI 651015) and FC221 (Reg. No. GP‐264, PI 651016) sugarbeet (Beta vulgaris L.) germplasm were released from 05‐FC1030‐15 (Sp) and 05‐FC1030‐16 (Sp) seed lots, respectively, and tested under those designations and as 03‐FC1030‐15 and 03‐FC1030‐16, respectively. They were developed by the USDA–ARS, at Fort Collins, CO, and at Salinas, CA, in cooperation with the Beet Sugar Development Foundation, Denver, CO. FC220 and FC221 are multigerm sugarbeet germplasm in fertile cytoplasm, segregating for self‐fertility and hypocotyl color. Both have resistance to root‐rotting strains (AG‐2‐2) of Rhizoctonia solani Kühn and are segregating for the Rz1 gene, which confers resistance to some strains of Beet necrotic yellow vein virus, the causal agent of rhizomania. These germplasm have moderate resistance to Aphanomyces cochlioides Drechs., which causes aphanomyces root rot (aphanomyces black root). FC221 is moderately resistant to curly top caused by Beet severe curly top virus. FC220 is resistant to the sugarbeet root aphid (Pemphigus sp.). Both germplasm are moderately susceptible to cercospora leaf spot, caused by Cercospora beticola Sacc. FC220 and FC221 have favorable yield characteristics when evaluated as lines or in experimental hybrids under rhizomania conditions at Salinas, CA. Under these conditions, FC220, as a line and in hybrid combinations, had a slight to significantly higher sucrose concentration than FC221.

Changes in the intraisolate genetic structure of Beet necrotic yellow vein virus populations associated with plant resistance breakdown

The causal agent of rhizomania disease, Beet necrotic yellow vein virus (BNYVV), typically produces asymptomatic root-limited infections in sugar beets ( Beta vulgaris) carrying the Rz1-allele. Unfortunately, this dominant resistance has been recently overcome. Multiple cDNA clones of the viral pathogenic determinant p25, derived from populations infecting susceptible or resistant plants, were sequenced to identify host effects on the viral population structure. Populations isolated from compatible plant–virus interactions (susceptible plant–wild type virus and resistant plant–resistant breaking variants) were large and relatively homogeneous, whereas those from the incompatible interaction (resistant plant–avirulent type virus) were small and highly heterogeneous. All populations from susceptible plants had the same dominant haplotype, whereas those from resistant cultivars had a different haplotype surrounded by a spectrum of mutants. Selection and diversification analyses suggest an evolutionary trajectory of BNYVV with positive selection for changes required to overcome resistance, followed by elimination of hitchhiking mutations through purifying selection.

Influence of Beet necrotic yellow vein virus on Sugar Beet Storability.

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) and storage losses are serious sugar beet production problems. To investigate the influence of BNYVV on storability, six sugar beet cultivars varying for resistance to BNYVV were grown in 2005 and 2006 in southern Idaho fields with and without BNYVV-infested soil. At harvest, samples from each cultivar were placed in an outdoor ventilated pile in Twin Falls, ID and were removed at 40-day intervals starting at the end of October. After 144 and 142 days in storage, sugar reduction across cultivars averaged 20 and 13% without and 68 and 21% with BNYVV for the 2005 and 2006 roots, respectively. In the December samplings, frozen root area was 1 and 2% without and 25 and 41% with BNYVV for the 2005 and 2006 roots, respectively. Root rot was always worse with stored roots from BYNVV-infested soil in December, January, and February samplings. Root weight loss was variable in 2005; however, in 2006, an increase in weight reduction always was associated with BNYVV-infested roots. In order to prevent losses in rhizomania-infested areas, cultivars should be selected for storability as well as rhizomania resistance.

Postharvest Storage Losses Associated with Rhizomania in Sugar Beet.

During storage of sugar beet, respiration and rots consume sucrose and produce invert sugar. Diseases that occur in the field can affect the magnitude of these losses. This research examines the storage of roots with rhizomania (caused by Beet necrotic yellow vein virus) and the effectiveness of rhizomania-resistant hybrids in reducing postharvest losses. Roots of susceptible hybrids from sites with rhizomania had respiration rates 30 days after harvest (DAH) that ranged from 0.68 to 2.79 mg of CO2 kg-1 h-1 higher than roots of the resistant hybrids. This difference ranged from 2.60 to 13.88 mg of CO2 kg-1 h-1 120 DAH. Roots of resistant hybrids from sites with rhizomania had 18 kg more sucrose per ton than roots from susceptible hybrids 30 DAH, with this difference increasing to 55 kg Mg-1 120 DAH. The invert sugar concentration of susceptible hybrids from sites with rhizomania ranged from 8.38 to 287 g per 100 g of sucrose higher than that for resistant hybrids 120 DAH. In contrast, differences between susceptible and resistant hybrids in respiration rate, sucrose loss, and invert sugar concentration in the absence of rhizomania were relatively small. Storage losses due to rhizomania can be minimized by planting resistant hybrids and processing roots from fields with rhizomania soon after harvest.

First report of Beet soil-borne virus on sugar beet in China

Beet soil-borne virus (BSBV) and Beet virus Q (BVQ) are two members of the genus Pomovirus that are transmitted by Polymyxa betae. BVQ and BSBV are commonly found in fields where Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania disease, is present (Henry & Jones, 1986; Koenig et al., 1998; Meunier et al., 2003). During the growing season of 2006, 26 roots of sugar beet exhibiting moderate to severe symptoms of rhizomania were collected from three fields located in Inner Mongolia and Xinjiang Provinces for a survey to determine whether BSBV and BVQ were present in China. Viral RNA was extracted from partially purified viruses of beet roots as described by Han et al. (2000) and tested by RT-PCR using three specific primer sets (BSBV: 5′-ATG GTT GAT CCG CGG TAT GAA G-3′ and 5′-CTA TTC AAC CCA GCG CAA ACC AAC-3′; BVQ: 5′-ATG GTT GAT CCA AGA TAT GAG C-3′ and 5′-CTA TGA GCC GGT CCA CTT CAA TCC-3′; and BNYVV: 5′-GCG GAT CCA TGT CGA GTG AA G GTA GA-3′ and 5′-CGA AGC TTG CTA TTG TCC GGG TGG-3′, based on Accession Nos NC003518, NC003511 and S71490 respectively) and designed to amplify coat protein genes for BSBV, BVQ and BNYVV respectively. Fifteen of the 26 beet samples gave positive reactions for BSBV, 21 for BNYVV and 14 for both BSBV and BNYVV. BVQ was not detected in any sugar beet sample tested. Subsequently, three RT-PCR products amplified in sugar beet samples collected from different locations with the primers specific to BSBV were cloned and sequenced (GenBank Accession Nos EF113300, EF210553 and EF210552). Sequence analysis revealed that these submitted sequences shared nucleotide identity of 98–99% with the German BSBV isolate (Accession No. NC003518). The partially purified viruses from infected sugar beet root were used for mechanical inoculation of Chenopodium quinoa and C. amaranticolor, and local lesions were observed on inoculated leaves. Furthermore, BSBV was also confirmed by RT-PCR (as described above) in the local lesions that appeared approximately 5 days after mechanical inoculation. Combined, the RT-PCR detection, nucleotide sequences and symptoms on inoculated host plants confirm the presence and first occurrence of BSBV in Inner Mongolia and Xinjiang. This work was partially supported by the National Natural Science Foundation of China (30471136 and 30671359).

Colicin N Binds to the Periphery of Its Receptor and Translocator, Outer Membrane Protein F

SummaryColicins kill Escherichia coli after translocation across the outer membrane. Colicin N displays an unusually simple translocation pathway, using the outer membrane protein F (OmpF) as both receptor and translocator. Studies of this binary complex may therefore reveal a significant component of the translocation pathway. Here we show that, in 2D crystals, colicin is found outside the porin trimer, suggesting that translocation may occur at the protein-lipid interface. The major lipid of the outer leaflet interface is lipopolysaccharide (LPS). It is further shown that colicin N binding displaces OmpF-bound LPS. The N-terminal helix of the pore-forming domain, which is not required for pore formation, rearranges and binds to OmpF. Colicin N also binds artificial OmpF dimers, indicating that trimeric symmetry plays no part in the interaction. The data indicate that colicin is closely associated with the OmpF-lipid interface, providing evidence that this peripheral pathway may play a role in colicin transmembrane transport.

Phylogenetic analysis of Beet necrotic yellow vein virus isolates from China

A survey detected Beet necrotic yellow vein virus (BNYVV) infection in six Chinese sugar-beet-growing regions. To study the diversity of virus isolates among the regions, nucleotide sequences of four proteins, namely CP, p25, p31, and p26, were determined and the amino acid sequences thus deduced were analyzed using sequence alignments and the phylogenetic method, respectively. Amino acid sequence analysis of CP revealed A-type isolates in Harbin, Hohhot, Baotou, Wuwei, and Jiuquan and B-type isolates in Hohhot and Changji; no Chinese isolate was found to cluster with European P-type isolates. Chinese p25 proteins clustered into three groups with seven tetrad motifs (positions 67-70). Of the seven, the tetrad ASHG has not been reported previously. Most Chinese p31 proteins clustered in p31-2 group, diverging from European p31 proteins. Isolates containing RNA 5 occurred in most of the investigated regions and were associated with both A-and B-types. Phylogenetic analyses of these four proteins showed complex patterns of genetic diversity among these Chinese isolates and indicated that the isolates of China and Japan were more closely related and may have a common origin.

Proteome changes in sugar beet in response to Beet necrotic yellow vein virus

Beet necrotic yellow vein virus (BNYVV) is a devastating sugar beet pathogen. Resistance is limited and resistance-breaking isolates are becoming problematic. Effective disease control strategies will come from a better understanding of disease and resistance. BNYVV-induced differential sugar beet protein expression was evaluated with multidimensional liquid chromatography. Of more than 1000 protein peaks detected in root extracts, 7.4 and 11% were affected by BNYVV in the resistant and susceptible genotypes, respectively. Using tandem MALDI-TOF-MS, 65 proteins were identified; differential expression of some was verified using RT-PCR. Proteomic data suggest involvement of systemic resistance components in Rz1-mediated resistance and phytohormones in symptom development.

Etiology of the sugar beet rhizomania

Beet necrotic yellow vein virus is responsible for sugar beet rhizomania. Root proliferation is characteristic of the viral infection and lead to sugar losses. Pathogenicity is particularly linked to the expression of RNA-3-encoded p25. The extensive use of viral tolerant crops allows maintenance of sugar yields but also permits viruliferous vector to be maintained and therefore the appearance of resistance breaking isolates. The resistance breaking isolates present some amino acid variations within the p25 protein sequence, a key determinant in BNYVV pathogenicity. Here, we will review the molecular biology of BNYVV, of its vector and the antiviral strategies that may be used against rhizomania.

Distribution and Molecular Characterization of Resistance-Breaking Isolates of Beet necrotic yellow vein virus in the United States.

Beet necrotic yellow vein virus (BNYVV) is the causal agent of rhizomania in sugar beet (Beta vulgaris). The virus is transmitted by the plasmodiophorid Polymyxa betae. The disease is controlled primarily by the use of partially resistant cultivars. During 2003 and 2004 in the Imperial Valley of California, partially resistant sugar beet cultivars with Rz1 allele seemed to be compromised. Field trials at Salinas, CA have confirmed that Rz1 has been defeated by resistance-breaking isolates. Distinct BNYVV isolates have been identified from these plants. Rhizomania-infested sugar beet fields throughout the United States were surveyed in 2004-05. Soil surveys indicated that the resistance-breaking isolates not only existed in the Imperial Valley and San Joaquin Valley of California but also in Colorado, Idaho, Minnesota, Nebraska, and Oregon. Of the soil samples tested by baited plant technique, 92.5% produced infection with BNYVV in 'Beta 6600' (rz1rz1rz1), 77.5% in 'Beta 4430R' (Rz1rz1), 45.0% in 'Beta G017R' (Rz2rz2), and 15.0% in 'KWS Angelina' (Rz1rz1+Rz2rz2). Analyses of the deduced amino acid sequence of coat protein and P-25 protein of resistance-breaking BNYVV isolates revealed the high percentage of identity with non-resistance-breaking BNYVV isolates (99.9 and >98.0%, respectively). The variable amino acids in P-25 proteins were located at the residues of 67 and 68. In the United States, the two amino acids found in the non-resistance-breaking isolates were conserved (AC). The resistance-breaking isolates were variable including, AF, AL, SY, VC, VL, and AC. The change of these two amino acids cannot be depended upon to differentiate resistance-breaking and non-resistance-breaking isolates of BNYVV.

SURVEYS OF BEET NECROTIC YELLOW VEIN VIRUS, BEET SOIL-BORNE VIRUS, BEET VIRUS Q AND POLYMYXA BETAE IN SUGAR BEET FIELDS IN IRAN

The main Iranian sugar beet (Beta vulgaris) growing areas were surveyed for the occurrence and incidence of Beet necrotic yellow vein virus (BNYVV), Beet soil-borne virus (BSBV) and Beet virus Q (BVQ). Root samples from 3,486 plants were collected from 184 commercial sugar beet fields of 14 provinces from randomly selected and symptomatic plants and analysed by tissue-blot immunoassay (TBIA). Serological diagnoses were confirmed by reverse transcription-polymerase chain reaction tests (RT-PCR) using specific primers. Based on TBIA data, BNYVV was prevalent (overall incidence of 52.4%), followed by BSBV (9.8%) and BVQ (1.4%). High levels of virus infections (more than 70%) were found in Ardabil, Esfahan, Fars, Khorasan and Zanjan provinces, whereas Khuzestan was apparently “virus-free”. The putative vector of the soil-borne viruses, Polymyxa betae, was also detected by RT-PCR in 179 fields surveyed.

Eradication of Polymyxa betae by Thermal and Anaerobic Conditions and in the Presence of Compost Leachate

AbstractThe abiotic conditions required for eradication of Polymyxa betae, the vector of Beet necrotic yellow vein virus in sugar beet, were investigated. Survival of resting spores of P. betae was determined under aerobic (30 min, 4 days and 21 days) and anaerobic (4 days) conditions under several temperature regimes in a water suspension and in leachate extracted from an aerobic compost heap. In water under aerobic conditions the lethal temperature was 60, 55 and 40°C for exposure times of 30 min, 4 days and 21 days, respectively. The effect of compost leachate and/or anaerobic conditions on survival of P. betae depended on temperature. After incubation for 4 days at 20°C, no significant effects of anaerobic conditions or leachate on the survival of P. betae were found. However, at 40°C for 4 days under anaerobic conditions, survival of P. betae was significantly lower than survival under aerobic conditions in water as well as in leachate. In leachate taken from an aerobic compost heap, aerobically incubated at 40°C for 4 days, survival of P. betae was significantly lower than survival in water at the same temperature. As anaerobic spots are prevalent in aerobic compost heaps, especially during the thermophilic phase, actual inactivation temperatures under composting conditions are likely to be lower than the temperatures we found for eradication in water under aerobic conditions.

RNA4-encoded p31 of beet necrotic yellow vein virus is involved in efficient vector transmission, symptom severity and silencing suppression in roots

RNA3 and RNA4 of beet necrotic yellow vein virus (BNYVV) are not essential for virus multiplication, but are associated with vector-mediated infection and disease development in sugar beet roots. Here, a unique role for RNA4 in virus transmission, virulence and RNA silencing suppression was demonstrated. Mutagenic analysis revealed that the RNA4-encoded p31 open reading frame (ORF) was involved in efficient vector transmission and slight enhancement of symptom expression in some Beta species. No effects of RNA4 on virus accumulation in infected tissue were observed. Furthermore, the p31 ORF was involved in the induction of severe symptoms by BNYVV in Nicotiana benthamiana plants without affecting viral RNA accumulation. In contrast, RNA3-encoded p25, previously identified as a major contributor to symptom induction in sugar beet, had no such effect on N. benthamiana. In two different silencing suppression assays, neither p31 nor p25 was able to suppress RNA silencing in leaves, but the presence of p31 enhanced a silencing suppressor activity in roots without alteration in viral RNA accumulation. Thus, BNYVV p31 plays a multifunctional role in efficient vector transmission, enhanced symptom expression and root-specific silencing suppression.

Efficient dsRNA-mediated transgenic resistance to Beet necrotic yellow vein virus in sugar beets is not affected by other soilborne and aphid-transmitted viruses

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is one of the most devastating sugar beet diseases. Sugar beet plants engineered to express a 0.4 kb inverted repeat construct based on the BNYVV replicase gene accumulated the transgene mRNA to similar levels in leaves and roots, whereas accumulation of the transgene-homologous siRNA was more pronounced in roots. The roots expressed high levels of resistance to BNYVV transmitted by the vector, Polymyxa betae. Resistance to BNYVV was not decreased following co-infection of the plants with Beet soil borne virus and Beet virus Q that share the same vector with BNYVV. Similarly, co-infection with the aphid-transmitted Beet mild yellowing virus, Beet yellows virus (BYV), or with all of the aforementioned viruses did not affect the resistance to BNYVV, while they accumulated in roots. These viruses are common in most of the sugar beet growing areas in Europe and world wide. However, there was a competitive interaction between BYV and BMYV in sugar beet leaves, as infection with BYV decreased the titres of BMYV. Other interactions between the viruses studied were not observed. The results suggest that the engineered resistance to BNYVV expressed in the sugar beets of this study is efficient in roots and not readily compromised following infection of the plants with heterologous viruses.

Partial nucleotide sequence analysis of Turkish isolates of Beet necrotic yellow vein virus (BNYVV) RNA‐3

A survey was carried out to detect Beet necrotic yellow vein virus (BNYVV) in soil samples using RT‐PCR and bait plant techniques from the sugar beet production area of Tokat, Turkey in 2001. More than 80% of the soil samples analyzed were found to be contaminated with the virus. The partial nucleotide sequence of cDNA corresponding to RNA‐3 of BNYVV isolates were analyzed for six different regions of Tokat province. All isolates were assigned to type A strains based on RFLP analysis and DNA sequences. Sequence comparison revealed differences at amino acid positions 35, 68, 71 and 179 of the P25 coding region amongst Turkish isolates. Additionally, all Turkish isolates were compared with Japanese, French, Kazakh, Italian and Belgian isolates.

Sequence variation within Beet necrotic yellow vein virus p25 protein influences its oligomerization and isolate pathogenicity on Tetragonia expansa

The p25 protein encoded by Beet necrotic yellow vein virus (BNYVV) RNA-3 is a pathogenicity determinant that has been implicated in symptom exacerbation on Chenopodiaceae hosts. Several p25 variants exist within natural isolates and p25 sequence variation may influence the degree of pathogenicity of such BNYVV isolates. Expression of p25 from natural A- and P-type isolates in the background of B-type BNYVV cDNA clones gave symptom discrepancies when compared to B-type p25 expression. Such pathogenicity fluctuation was not due to a different subcellular localization of p25 but was correlated with the nature of the tetrad motif present between amino acid residues 67–70, as well as with the capacity of p25 to self-associate and to activate transcription in a yeast one-hybrid system. Our data suggest that the complete sequence of p25 is required for its functions and the identified sequence variations may contribute to correct folding of the protein.

Mutations Associated with Resistance-Breaking Isolates of Beet necrotic yellow vein virus and Their Allelic Discrimination Using TaqMan Technology

ABSTRACT Genetic resistance in sugar beet (Beta vulgaris) to Beet necrotic yellow vein virus (BNYVV), which causes the disease rhizomania, is conferred by the single dominant gene Rz1. However, since 2002, Rz1 cultivars grown in the Imperial Valley of California have been increasingly damaged by a new strain of BNYVV. Viral RNA 3 was extracted from asymptomatic and symptomatic sugar beets and, after amplification and sequencing of a region including the p25 cistron, two polymorphic sites, A67V and D135E, associated with the capability of the virus to overcome resistance were identified. Using the real-time reverse transcription-polymerase chain reaction allelic discrimination technique, TaqMan probes designed to detect the responsible nucleotide substitutions permitted the differentiation between wild type (WT) and resistance-breaking (RB) isolates. This method also allowed easy detection of mixed infections by giving a heterozygous call, which was verified by DNA sequencing of individual clones. The capability of this technology to typify numerous isolates facilitated the analysis of the spatial distribution of virus haplotypes in the field. Thus, RB variants were mostly baited from yellow strips with high incidence of rhizomania, whereas WT variants predominated in the surrounding green areas. Mixed infections were found mainly in green areas and transitional zones. The predominance of the RB isolates in yellow strips suggests that they have gained fitness in Rz1 cultivars and will eventually become the dominant haplotype.