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Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is a yield-limiting sugar beet disease that was observed to influence root resistance to freezing in storage. Thus, studies were conducted to gain a better understanding of the influence of BNYVV and freezing on sugar beet roots to improve pile management decisions. Roots from five commercial sugar beet cultivars (one susceptible and four resistant to BNYVV) were produced in fields under high and trace levels of rhizomania pressure and subjected to storage using five temperature regimes ranging from 0 to −4.4°C for 24 h. After cold treatment, eight-root samples were stored in a commercial indoor storage building (set point 1.1°C) for 50 days in 2014 and 57 days in 2015. Internal root temperature, frozen and discolored tissue, and moisture and sucrose loss were evaluated. The air temperature at 0, −1.1, and −2.2°C matched internal root temperature but internal root remained near −2.2°C when air temperature was dropped to −3.3 and −4.4°C. In a susceptible cultivar produced under high rhizomania pressure, the percentage of frozen tissue increased (P < 0.0001) from an average of 0 to 7% at 0, −1.1, and −2.2°C up to 16 to 63% at −3.3°C and 63 to 90% at −4.4°C, depending on year. Roots from the susceptible cultivar produced under low rhizomania pressure and those from the resistant cultivars from both fields only had elevated (P ≤ 0.05) frozen tissue at −4.4°C in 15 of 18 cultivar–year combinations. Frozen tissue was related to discolored tissue (r2 = 0.91), weight loss (r2 = 0.12 to 0.28), and sucrose reduction (r2 = 0.69 to 0.74). Consequently, BNYVV will not only lead to yield and sucrose loss in susceptible sugar beet cultivars but also to more frozen root tissue as temperatures drop below −2.2°C. Based on these observations, the air used to cool roots in nonfrozen sugar beet piles throughout the winter should not drop below −2.2°C to maximize sucrose retention.

The RNA silencing-suppression properties of Beet necrotic yellow vein virus (BNYVV) and Beet soil-borne mosaic virus (BSBMV) cysteine-rich p14 proteins have been investigated. Suppression of RNA silencing activities were made evident using viral infection of silenced Nicotiana benthamiana 16C, N. benthamiana agroinfiltrated with green fluorescent protein (GFP), and GF-FG hairpin triggers supplemented with viral suppressor of RNA silencing (VSR) constructs or using complementation of a silencing-suppressor-defective BNYVV virus in Chenopodium quinoa. Northern blot analyses of small-interfering RNAs (siRNAs) in agroinfiltration tests revealed reduced amounts of siRNA, especially secondary siRNA, suggesting that benyvirus VSR act downstream of the siRNA production. Using confocal laser-scanning microscopy imaging of infected protoplasts expressing functional p14 protein fused to an enhanced GFP reporter, we showed that benyvirus p14 accumulated in the nucleolus and the cytoplasm independently of other viral factors. Site-directed mutagenesis showed the importance of the nucleolar localization signal embedded in a C4 zinc-finger domain in the VSR function and intrinsic stability of the p14 protein. Conversely, RNA silencing suppression appeared independent of the nucleolar localization of the protein, and a correlation between BNYVV VSR expression and long-distance movement was established.

Beet necrotic yellow vein virus (BNYVV) causes one of the most economically destructive diseases of sugar beet (Beta vulgaris), rhizomania, which may reduce sugar yield by 80%. This field investigation was conducted to evaluate the interactions between spinach genotypes and different BNYVV strains, and to determine whether BNYVV is transmitted through spinach seeds. Eight commercial spinach cultivars were planted in two BNYVV-infested fields and two control fields in Salinas, CA in 2009. Spinach plants in the BNYVV-infested fields showed disease symptoms of yellow-green or light-green vein clearing, mottling, or yellow-green chlorotic lesions on younger leaves as early as 28 days after planting (four- to six-true leaf stage). Leaves may also become stiff, more crinkled, and necrotic. There was an increase of lateral roots and leaf number but a decrease in leaf weight compared to healthy plants. Infected plants often became stunted, deformed, wilted, and dead. Symptomatic leaves and roots from plants with or without leaf symptoms in BNYVV-infested fields all tested positive for BNYVV by enzyme-linked immunosorbent assay. A more aggressive (resistance-breaking) strain of BNYVV led to higher disease incidence in spinach than in the wild type. BNYVV was not transmitted through spinach seeds. There were significant differences in disease development among cultivars, with disease incidence ranging from 8 to 44%, suggesting that genetic improvement of BNYVV resistance through spinach breeding should be feasible.

The genome of most Beet necrotic yellow vein virus (BNYVV) isolates is comprised of four RNAs. The ability of certain isolates to overcome Rz1-mediated resistance in sugar beet grown in the United States and Europe is associated with point mutations in the pathogenicity factor P25. When the virus is inoculated mechanically into sugar beet roots at high density, the ability depends on an alanine to valine substitution at P25 position 67. Increased aggressiveness is shown by BNYVV P type isolates, which carry an additional RNA species that encodes a second pathogenicity factor, P26. Direct comparison of aggressive isolates transmitted by the vector, Polymyxa betae, has been impossible due to varying population densities of the vector and other soilborne pathogens that interfere with BNYVV infection. Mechanical root inoculation and subsequent cultivation in soil that carried a virus-free P. betae population was used to load P. betae with three BNYVV isolates: a European A type isolate, an American A type isolate, and a P type isolate. Resistance tests demonstrated that changes in viral aggressiveness towards Rz1 cultivars were independent of the vector population. This method can be applied to the study of the synergism of BNYVV with other P. betae-transmitted viruses.

Theoretical models predict that, under restrictive host conditions, virus populations will exhibit greater genetic variability. This virus response has been experimentally demonstrated in a few cases but its relation with a virus's capability to overcome plant resistance is unknown. To explore the genetic host effects on Beet necrotic yellow vein virus (BNYVV) populations that might be related to resistance durability, a wild-type virus isolate was vector inoculated into partially resistant Rz1, Rz2, and susceptible sugar beet cultivars during a serial planting experiment. Cloning and sequencing a region of the viral RNA-3, involving the pathogenic determinant p25, revealed that virus diversity significantly increased in direct proportion to the strength of host resistance. Thus, whereas virus titers were highest, intermediate, and lowest in susceptible, Rz1, and Rz2 plants, respectively; the average number of nucleotide differences among single-plant populations was 0.8 (±0.1) in susceptible, 1.4 (±0.1) in Rz1, and 2.4 (±0.2) in Rz2 genotypes. A similar relationship between host restriction to BNYVV root accumulation and virus genetic variability was detected in fields of sugar beet where these specific Rz1- and Rz2-mediated resistances have been defeated.

Breakdown of sugar beet Rz1-mediated resistance against Beet necrotic yellow vein virus (BNYVV) infection was previously found, by reverse genetics, to be caused by a single mutation in its p25 gene. The possibility of alternative breaking mutations, however, has not been discarded. To explore the natural diversity of BNYVV in the field and its effects on overcoming Rz1, wild-type (WT) and resistance-breaking (RB) p25 genes from diverse production regions of North America were characterized. The relative titer of WT p25 was inversely correlated with disease expression in Rz1 plants from Minnesota and California. In Minnesota, the predominant WT p25 encoded the A67C68 amino acid signature whereas, in California, it encoded A67L68. In both locations, these WT signatures were associated with asymptomatic BNYVV infections of Rz1 cultivars. Further analyses of symptomatic resistant plants revealed that, in Minnesota, WT A67C68 was replaced by V67C68 whereas, in California, WT A67L68 was replaced by V67L68. Therefore, V67 was apparently critical in overcoming Rz1 in both pathosystems. The greater genetic distances between isolates from different geographic regions rather than between WT and RB from the same location indicate that the underlying C to U transition originated independently in both BNYVV lineages.

Beet necrotic yellow vein virus (BNYVV) induces the most important disease threatening sugar beet. The growth of partially resistant hybrids carrying monogenic dominant resistance genes stabilize yield but are unable to entirely prevent virus infection and replication. P25 is responsible for symptom development and previous studies have shown that recently occurring resistance-breaking isolates possess increased P25 variability. To better understand the viral pathogenicity factor's interplay with plant proteins and to possibly unravel the molecular basis of sugar beet antivirus resistance, P25 was applied in a yeast two-hybrid screen of a resistant sugar beet cDNA library. This screen identified candidate proteins recognized as orthologues from other plant species which are known to be expressed following pathogen infection and involved in plant defense response. Most of the candidates potentially related to host-pathogen interactions were involved in the ubiquitylation process and plants response to stress, and were part of cell and metabolism components. The interaction of several candidate genes with P25 was confirmed in Nicotiana benthamiana leaf cells by transient agrobacterium-mediated expression applying bimolecular fluorescence complementation assay. The putative functions of several of the candidates identified support previous findings and present first targets for understanding the BNYVV pathogenicity and antivirus resistance mechanism.

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.

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.

Historically, Beet necrotic yellow vein virus (BNYVV), which causes the disease rhizomania of sugar beet, has caused major reductions in root yield and quality wherever it occurred. In the United States, the disease was first identified in California in 1984 (12), but it now occurs in every major sugar beet production region in the country. Fortunately, strong genetic tolerance to BNYVV, conferred by the Rz1 gene, was identified soon after rhizomania was discovered in the United States, and it has been incorporated into regionally adapted cultivars that allow profitable sugar beet production in areas infested with the pathogen. Plants possessing Rz1 are susceptible to infection by P. betae and BNYVV, but virus titers remain low, and typically, infected plants exhibit normal, asymptomatic growth. However, in the Imperial Valley of California in 2002, plants in a field planted to a rhizomaniatolerant cultivar began to express symptoms of rhizomania (47). Large strips of diseased plants occurred across the field, and it was soon verified that certain isolates of BNYVV from the California Imperial Valley (CIV-BNYVV) had overcome genetic resistance. In other regions of the United States, individual plants, or clusters of plants, in fields planted to rhizomaniatolerant cultivars have also become infected by BNYVV and developed diagnostic symptoms of severe rhizomania. Although patterns of disease development have varied between California fields and those in other production regions in the United States, the breakdown of genetic resistance has caused considerable concern among those involved in sugar beet production. The purpose of this article is to provide an update on rhizomania and the activities that are currently underway to manage this continuing threat to the U.S. sugar beet industry. A review on the detection and distribution of rhizomania and soilborne viruses associated with sugar beet production in the United States (61), and a second more in-depth review on BNYVV and its vector, Polymyxa betae (Keskin) (60), have been published.

In plants, RNA silencing is part of a defense mechanism against virus infection but there is little information as to whether RNA silencing-mediated resistance functions similarly in roots and leaves. We have obtained transgenic Nicotiana benthamiana plants encoding the coat protein readthrough domain open reading frame (54 kDa) of Beet necrotic yellow vein virus (BNYVV), which either showed a highly resistant or a recovery phenotype following foliar rub-inoculation with BNYVV. These phenotypes were associated with an RNA silencing mechanism. Roots of the resistant plants that were immune to foliar rub-inoculation with BNYVV could be infected by viruliferous zoospores of the vector fungus Polymyxa betae, although virus multiplication was greatly limited. In addition, virus titer was reduced in symptomless leaves of the plants showing the recovery phenotype, but it was high in roots of the same plants. Compared with leaves of silenced plants, higher levels of transgene mRNAs and lower levels of transgene-derived small interfering RNAs (siRNAs) accumulated in roots. Similarly, in nontransgenic plants inoculated with BNYVV, accumulation level of viral RNA-derived siRNAs in roots was lower than in leaves. These results indicate that the RNA silencing-mediated resistance to BNYVV is less effective in roots than in leaves.

Soils naturally infested with cultures of aviruliferous Polymyxa betae and viruliferous P. betae carrying two sugar beet benyviruses, Beet necrotic yellow vein virus (BNYVV) and Beet soilborne mosaic virus (BSBMV), alone and in combination, were compared with noninfested soil for their effects on seedling emergence, plant fresh weight, and virus content as measured by enzyme-linked immunosorbent assay (ELISA). Studies examined sugar beet with and without resistance to the disease rhizomania, caused by BNYVV. The Rz gene, conferring resistance to BNYVV, did not confer resistance to BSBMV. BSBMV ELISA values were significantly higher in single infections than in mixed infections with BNYVV, in both the rhizomania-resistant and -susceptible cultivars. In contrast, ELISA values of BNYVV were high (8 to 14 times the healthy mean) in single and mixed infections in the rhizomania-susceptible cultivar, but were low (approximately three times the healthy mean) in the rhizomania-resistant cultivar. Results indicate BNYVV may suppress BSBMV in mixed infections, even in rhizomania-resistant cultivars in which ELISA values for BNYVV are extremely low. Soils infested with P. betae, and with one or both viruses, showed significantly reduced fresh weight of seedlings, and aviruliferous P. betae significantly decreased sugar beet growth in assays.

Beet necrotic yellow vein virus (BNYVV) causes rhizomania of sugar beet (Beta vulgaris), which is characterized by stunting, leaf necrosis, constriction of the taproot, and extensive lateral- and feeder-root proliferation. Beet soilborne mosaic virus (BSBMV) causes similar but typically less severe symptoms than those of BNYVV. Both viruses are widely distributed in sugar beet-growing regions of the United States. Both viruses are vectored by the soilborne plasmodiophorid Polymyxa betae Keskin and are very similar in morphology and biology, sharing many characteristics in common. In 1999, soil samples were collected from sugar beet fields in Colorado, Minnesota, North Dakota, and Texas to determine the spatial association and covariation of the viruses in sugar beet fields. In 2000, additional samples were collected from fields in Minnesota and North Dakota. Over the 2-year period, soil samples were collected from 11 fields in various quadrat sizes. The viruses were assayed by growing sugar beet (cv. Beta 1395) in the soil samples and their incidence was determined using the double-antibody sandwich enzyme-linked immunosorbent assay. Both viruses were detected in samples from all fields but were in greater frequencies singly than in association. Association of the two viruses (where both viruses were detected in the same sample or bait plant) varied among fields, ranging from 1 to 42%. Geostatistical analysis revealed that both viruses, in large part, exhibited similar spatial patterns. In all but two fields, there was no spatial dependence among the sampling locations at sampled grid sizes. Their semivariances were constant at all separation distances in all directions indicating random spatial patterns. Overall, the spatial pattern of BNYVV appeared to be a little more structured than that of BSBMV. Even though both viruses are transmitted by the same vector and also exhibited similar distribution patterns, the incidence of one virus may not be estimated from that of the other due to lack of strong association and spatial dependence. However, similarity in spatial patterns of the two suggests that a similar sampling method can be employed for both viruses.

A field experiment was conducted to quantify the effects of different irrigation frequencies on sugar beet yield in pathogen-infested soils. Four irrigation regimes (every 2, 3, 4, and 5 weeks) and four inoculation treatments (beet necrotic yellow vein virus [BNYVV], beet soilborne mosaic virus [BSBMV], BNYVV+BSBMV, and a noninoculated control) were arranged in a split-plot design and replicated four times. Irrigation frequency and virus infection affected disease severity and yield. Sugar beets irrigated every 4 weeks had the lowest disease severity, and yield was not significantly different from the every 2 weeks frequency. Sucrose content was higher for beets in the 4-week irrigation treatment compared with the 2- and 3-week frequencies. Beets inoculated with BNYVV had higher disease severity and lower root yield than beets inoculated with BSBMV and BNYVV+BSBMV. A greenhouse experiment was conducted to evaluate the effect of water level on disease severity and water use in sugar beet. Four treatments (BNYVV, BSBMV, BNYVV+BSBMV, and a noninoculated control) and three water levels (pot capacity [PC], 75% PC, and 50% PC) were arranged in a split-plot design and replicated five times. Pots of each treatment were weighed every other day to determine evapotranspiration. Evaporation was determined from unplanted pots, and plant transpiration was calculated by the difference. Beets irrigated at 75% pot capacity showed minimal disease incidence and a root weight comparable to the fully irrigated healthy control. Plants in the BNYVV treatment had a significantly higher disease severity than beets infected by BSBMV or BNYVV+BSBMV. Root weights and plant water use were significantly affected by virus infection. Beets in the BNYVV+BSBMV treatment had a significantly higher root dry weight and water use than beets in the BNYVV treatment, suggesting that BSBMV reduced the impact of disease caused by BNYVV.

Levels of beet necrotic yellow vein virus (BNYVV), as measured by triple-antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), were compared with biological evaluations in representative commercial and experimental sugar beet cultivars developed for production in the United States and ranging in their reactions to rhizomania from uniformly susceptible to highly resistant. TAS-ELISA was specific for BNYVV and did not react with related soilborne sugar beet viruses. Differences in absorbance (A405nm) values measured in eight cultivars closely correlated with the dosage and frequency of the Rz allele, which conditions resistance to BNYVV. A diploid (Rzrz) hybrid had a significantly lower absorbance value (less virus) than a similar triploid (Rzrzrz) hybrid. Cultivars that segregated (Rzrz:rzrz) had higher absorbance values than uniformly resistant (Rzrz) hybrids, as was expected. For all cultivars, absorbance values decreased as the season progressed. Absorbance value was significantly positively correlated with rhizomania disease index score and negatively correlated with individual root weight, plot root weight, and sugar yield. This information should be useful in resistance-breeding and -evaluation programs and in the sugar industry when considering cultivar choice, inoculum production, and future crop rotations.

Cell-to-cell movement of beet necrotic yellow vein furovirus is controlled by three slightly overlapping genes on RNA 2 called the triple gene block (TGB) encoding, in order, P42, P13, and P15. Synthesis of P42 is directed by subgenomic RNA 2suba while synthesis of both P13 and P15 is probably directed by a dicistronic subgenomic RNA, 2subb. For complementation experiments, each TGB protein gene was inserted into a “replicon” derived from viral RNA 3. In mixed infections, the replicons expressing P42 and P13 complemented RNA 2 mutants defective in the corresponding gene. A P15-containing replicon did not complement a P15-defective RNA 2 but complementation was observed with a dicistronic replicon containing the P15 gene placed behind the P13 gene. In mixed infections with wild-type viral RNAs, the P15-containing replicon did not inhibit viral RNA replication in protoplasts but blocked local lesion formation on leaves. Infection of leaves was also inhibited by an RNA3-derived replicon containing the third TGB gene from another furovirus, peanut clump virus. The results are consistent with a model in which viral cell-to-cell movement requires production of appropriate relative amounts of P13 and P15, and their expression from a dicistronic subgenomic RNA provides a mechanism for coordinating their synthesis.

Sugar beet (Beta vulgaris var. saccharifera L.) is the main crop used for the production of sugar in Croatia. Beet yellows virus (BYV), type member of the genus Closterovirus, is characterized by flexuous, filamentous particles which are transmitted by several aphid species in a semipersistent manner (Agranovsky and Lesemann 2000). This widely spread virus is reported from most of the sugar beet-growing areas of the world, including Europe. In the geographic region that was once the former Yugoslavia, the presence of BYV was suspected based on field symptoms reported from Serbia (Nikolić 1951) and Croatia (Panjan 1951). During the 2013 and 2014 growing season, the presence of sugar beet plants with symptoms of yellowing was sporadically observed in commercial fields located in eastern Croatia (i.e., Tovarnik, Bošnjaci, and Virovitica). In late July 2014, a significant number of sugar beet plants, located mainly on the field edges, with the aforementioned symptoms were noticed in experimental fields of various sugar beet cultivars located at the University of Zagreb, Faculty of Agriculture. In total, 102 plants collected from commercial fields and 12 plants from the university experimental fields with cvs. Torda and Libero were selected and screened using ELISA for the presence of Beet necrotic yellow vein virus (BNYVV), Beet mosaic virus (BtMV), Beet mild yellowing virus (BMYV), Beet western yellows virus (BWYV), and BYV. To conduct the diagnostic assays, commercial ELISA kits from Loewe Biochemica GmbH (BNYVV, BtMV, and BYV) and Sediag (BMYV and BWYV) were used. BYV was confirmed in five plants from commercial fields and in all the plants from Zagreb. Due to the presence of single infections in plants from Zagreb, and in order to determine the detrimental effects of BYV, all plants from the study field control plots (104 of Torda and 103 of Libero) were tested by ELISA. Tests revealed the presence of BYV in 18 (17.3%) plants of Torda and in 34 (33%) plants of Libero. BYV infections averaged a 9 to 10% reduction of pure root yield and sugar content in both cultivars compared with BYV-free plants. One ELISA-positive plant per cultivar was chosen for the extraction of total RNA using the QIAGEN RNeasy plant mini kit according to manufacturer’s instructions. In both plants, the presence of BYV was confirmed by RT-PCR using four set of diagnostic primers (Kundu and Ryšánek 2004). PCR products from both samples, named BYV- CRO-T from Torda and BYV-CRO-L from Libero, were purified and sequenced in both directions (Genbank Accession Nos. KP704263 to KP704268). Nucleotide sequence alignment of the DNA fragments for both Croatian isolates, including the C-terminal part of L-Pro and N-terminal part of MET and HSP70, showed 99.2, 99.7 and 100% similarity, respectively. Nucleotide comparisons of Croatian isolates with Californian (Genbank Accession No. AF056575) showed a 97% similarity for L-Pro and HSP70 and a 99% for MET. To our knowledge, this is the first report of Beet yellows virus in Croatia and its detrimental effect on actual sugar beet cultivars grown under Croatian environmental conditions.

The objective of this work was to determine whether Beet virus Q (BVQ), a member of the genus Pomovirus, is present in Poland. BVQ, like Beet necrotic yellow vein virus (BNYVV), is transmitted by Polymyxa betae Keskin. Earlier, BVQ was described as the Wierthe serotype of Beet soilborne virus (BSBV). Now, on the basis of its genomic properties (2), BVQ is recognized as a distinct virus species. BVQ is often found in fields where BSBV and BNYVV are present (4). During the fall of 2005, five plants of a cultivar susceptible to rhizomania (cv. Alyssa) and five resistant to rhizomania (cv. Henrietta) were collected from a field in the Wielkopolska Region of Poland, where BSBV and BNYVV had been previously identified, and tested for BVQ (1). All samples were analyzed by a double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) with antiserum against BNYVV (Bio-Rad, Hercules, CA). Rhizomania was identified only in sugar beet samples of the susceptible variety. The same samples were then tested using a triple antibody sandwich (TAS)-ELISA with commercial antisera against BSBV/BVQ (As-0576.2) and BSBV (As-0576.1) (DSMZ, Braunschweig, Germany). Nine sugar beet plants gave positive reactions with antiserum against BSBV/BVQ and negative reactions with antiserum specific to BSBV. Total RNA extracted from roots of 10 beet samples was then tested using a multiplex reverse transcription-polymerase chain reaction (mRT-PCR) and specific primers designed to amplify a fragment of the RNA2 for BNYVV and BVQ (3). The primers specifically amplified fragments of 545 bp and 291 bp of the BNYVV and BVQ, respectively. BNYVV was detected in all five samples from susceptible sugar beet plants. The presence of BVQ was confirmed in nine of the sugar beer plants, and the RT-PCR products were sequenced. Sequence analysis of the 206-nt amplicon sequence of the Polish isolate of BVQ (GenBank Accession No. DQ309444) indicated 97% nucleotide and 94% amino acid sequence identity with the previously published sequence of BVQ (GenBank Accession No. AJ223596) (2). To my knowledge, this is the first report of the natural occurrence of BVQ on sugar beet in Poland. In Europe, it has been previously reported in Belgium, Bulgaria, France, Germany, Hungary, Italy, the Netherlands, Spain, and Sweden (3,4). References: (1) N. Borodynko et al. Plant Dis. 90:112, 2006. (2) R. Koenig et al. J. Gen. Virol. 79:2027, 1998. (3) A. Meunier et al. Appl. Environ. Microbiol. 69:2356, 2003. (4) C. Rubies Autonell et al. Plant Dis. 90:110, 2006.

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV) and vectored by the soilborne fungus, Polymyxa betae Keskin, is one of the most economically damaging diseases affecting sugar beet (Beta vulgaris L.) worldwide and has been found in most sugar beet-growing areas of the United States (2). During harvest in October 2000, sugar beet plants exhibiting typical symptoms of rhizomania (1) were found in a field near Paterson, WA. Sugar beet had been planted in the field in 1999 and 2000, but prior to this, the field had not been planted with sugar beet for approximately 20 years. Symptomatic roots from the field exhibited stunting, vascular discoloration, and proliferation of lateral rootlets. Leaves of affected plants were chlorotic. Four soil samples were taken from symptomatic areas of the field and diluted with an equal amount of sterile sand. Seeds of rhizomania-susceptible sugar beet cv. Beta 8422 were planted in the soil and sand mix and maintained in a controlled environment at 24°C and 12 h of daylight at one location and in the greenhouse at another. After 8 weeks, enzyme-linked immunosorbent assay (ELISA) was performed on roots of plants grown at each location. Triple-antibody sandwich (TAS) ELISA (Agdia, Inc., Elkhart, IN) was conducted at the University of Idaho, Twin Falls, ID and double-antibody sandwich (DAS) ELISA was performed at USDA-ARS, Salinas, CA, with antiserum specific for BNYVV (2). Two of four samples were positive for BNYVV in the ELISA tests at both locations based on absorbance values at least three times those of healthy controls. TAS-ELISA tests were conducted on roots collected in July 2001 from a field in Washington, 12.9 km from the first field, as well as from a field across the Columbia River near Boardman, OR. Samples from both fields tested positive for BNYVV. All three fields are within 24 km of one another. Four additional fields have subsequently been confirmed to be infected with BNYVV in this region, based on symptomology and ELISA. There are approximately 3,240 ha of sugar beet grown in the region, and growers have been advised as a result of this confirmation to plant resistant cultivars and increase the sugar beet rotation interval with nonhost crops to a minimum of 4 years. References: (1) J. E. Duffus. Rhizomania. Pages 29–30 in: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus, eds. The American Phytopathological Society, St. Paul, MN, 1986. (2) G. C. Wisler et al. Plant Dis. 83:864, 1999.

Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania disease on sugar beet, has been reported in Belgium for more than 16 years. Other soilborne viruses belonging to the genus Pomovirus, such as Beet soilborne virus (BSBV) (3) and Beet virus Q (BVQ) (1), are suspected pathogens of sugar beets grown in Belgium. During the 2000 growing season, more than 20 fields showing rhizomania-like and yellowing symptoms on sugar beet leaves were investigated for the presence of BVQ, BNYVV, and BSBV. All samples were checked by enzyme-linked immunosorbent assay (ELISA) using commercial BNYVV (Sanofi Diagnostics Pasteur, Marnes-La-Coquette, France) and BSBV/BVQ (DSMZ, Braunschweig, Germany - AS-0576 polyclonal, AS-0576/2 MAb) antisera. RNA was extracted from sugar beet rootlets using an RNeasy extraction kit (Qiagen, Hilden, Germany), before performing a reverse transcription-polymerase chain reaction (RT-PCR) using primers (5′-GCTGGAGTATATCACCGATGAC-3′ and 5′-AAAATC TCGGATAGCATCCAAC-3′) designed to specifically amplify a 510-bp region of BVQ RNA-1. The presence of BSBV and BNYVV was also checked by RT-PCR using previously described primers (1,2). The BVQ-derived PCR product was sequenced and proved to be more than 99% identical to the Wierthe BVQ isolate nucleotide sequence. Soil transmission of BVQ was demonstrated through a bioassay using soil dilutions with quartz and sugar beet cv. Cadyx as bait. After 6 weeks, BVQ was detected by RT-PCR in bait plants. The putative vector, Polymyxa betae, was identified by lactophenol-cotton blue staining of the roots followed by microscopic examination. BVQ produces irregularly shaped local lesions that appear ≈5 days after mechanical inoculation and tend to spread along veins. BVQ was detected in six fields located in the Polders Region and Brabant Province of Belgium. BVQ was always found in sugar beet samples coinfected with BNYVV and BSBV. The economic significance of BVQ and its interaction with other viruses is not known. References: (1) R. Koenig et al. J. Gen. Virol. 79:2027, 1998. (2) M. Saito et al. Arch. Virol. 141:2163, 1996. (3) M. Verhoyen and M. Van den Bossche. Parasitica. 44:71, 1987.

A 3-year study was initiated in 1992 to map the spread of beet necrotic yellow vein virus (BNYVV) from known point sources of inoculum by irrigation and tillage practices. The experiment each year consisted of four plots, each containing 12 30-m rows, on 76-cm centers. Sugar beet seeds (cv. HH39) coated with BNYVV-infested Polymyxa betae were planted in the first 3 m of the two outside rows of each plot and constituted the point sources of inoculum. The remaining plot area was planted with uninfested seeds. Plots were furrow irrigated every 2 weeks. Plant and soil samples were collected from the point source areas and other predetermined locations in each plot before tillage operations. Plant roots were assayed by indirect double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) for BNYVV incidence. Soil samples were planted with sugar beet seeds in the greenhouse, and after 10 to 12 weeks, roots of bait plants were assayed for BNYVV. To further evaluate movement, soil samples were collected from the previous locations after tillage events and after a second sugar beet crop before being bioassayed. All plant samples taken from point sources exhibited typical symptoms of rhizomania, and both plant and soil samples tested positive for BNYVV in DAS-ELISA tests. Out of 336 plants collected in the field from non-point-source areas, only 1 tested positive. Before tillage events, 2% of the soil samples were positive for BNYVV for the first experiment and 0.9% tested positive the second, suggesting negligible movement of viruliferous P. betae by irrigation. After tillage and harvest operations, 9 and 6% of the soil samples were infested for the first and second experiments, respectively. After a successive sugar beet crop, 15% of the soil samples were positive for BNYVV in the first experiment and 12% in the second. Our results show that physical movement of soil during tillage and harvest operations exert a much greater influence on spread of BNYVV than furrow irrigation, which contradicts the generally accepted concept that viruliferous P betae is rapidly disseminated by irrigation.

Field studies were conducted in 1991 and 1993 to evaluate the effectiveness of Tolene II fumigation and rhizomania-tolerant cultivars to control a complex of soilborne pathogens (Rhizoctonia solani, Aphanomyces cochlioides, Fusarium oxysporum f. sp. betae, and beet necrotic yellow vein virus). Fifteen cultivars (13 rhizoimania-tolerant and two rhizomania-susceptible) were included in a randomized complete block split-plot design with six replications in which main plots were fumigated or nonfumigated and cultivars were subplots

The Texas sugar beet-growing area was surveyed to determine the incidence of beet necrotic yellow vein virus (BNYVV), beet distortion mosaic virus (BDMV), and an unnamed soilborne sugar beet virus designated as Texas 7 (Tx7). In late 1990, 302 soil samples were collected from seven Texas counties and one New Mexico county from fields scheduled for 1991 production. Sugar beet seed was planted in the soil samples, and root tissue was later harvested and tested by ELISA. Of 174 soil samples screened for BNYVV, 19 were positive. Of 128 samples tested for BNYVV and Tx7, 12 were positive for Tx7, three were positive for BNYVV, and 23 were positive for both BNYVV and Tx7 [...]

Oligonucleotide primers based on published sequence data for beet necrotic yellow vein virus (BNYVV) were synthesized for use in the reverse transcriptase polymerase chain reaction (RT-PCR) to differentiate beet soilborne mosaic virus (BSBMV) from BNYVV. Primers designed for the 3' end of BNYVV RNA 1 were effective in PCR amplification of a product of the predicted size, approximately 1,056 bp, from extracts of plants infected by BNYVV. The same primer pair also directed the amplification of a PCR product of approximately 1,000 bp from extracts of plants infected by BSBMV. If extracts from plants infected with BNYVV were mixed with those from plants infected with BSBMV, the primer pair allowed the amplification of only BNYVV

An experiment was initiated to determine how sugar beets are affected by Aphanomyces cochlioides and beet necrotic yellow vein virus (BNYVV), the causal agents of Aphanomyces root rot and rhizomania, respectively. The experiment was conducted in a controlled temperature box maintained at 27±2 C. Treatments consisted of soil infested with Aphanomyces, BNYVV, both pathogens combined, and an untreated control. At 8 and 12 wk after planting, leaf and petiole weights and leaf areas were taken. At harvest, tops were removed, and the soil cores were divided into three 15-cm segments and washed. After 8 wk, leaf weights and leaf areas for the control treatment were significantly higher than those for the pathogen treatments [...]

A method of inoculating sugar beet with viruliferous Polymyxa betae for use in field and greenhouse studies was evaluated for two years (1991-1992). Seeds of sugar beet cultivar HH39 were coated with powdered sugar beet roots containing beet necrotic yellow vein virus (BNYVV)-infested P. betae cystosori. Two percent methyl cellulose was used as the carrier at rates of 1:20:20 and 1:10:10 (w/v/w) inoculum/methyl cellulose/seed. Seeds were planted in field plots and maintained by conventional agronomic practices. During 1991, plots were sampled and tested for BNYVV incidence twice between planting and harvest. The second year, plots were sampled once [...]