Occurrence and Relative Incidence of Viruses Infecting Soybeans in Iran

Occurrence, distribution, and genetic diversity of faba bean viruses in China

With worldwide cultivation, the faba bean (Vicia faba L.) stands as one of the most vital cool-season legume crops, serving as a major component of food security. China leads global faba bean production in terms of both total planting area and yield, with major production hubs in Yunnan, Sichuan, Jiangsu, and Gansu provinces. The faba bean viruses have caused serious yield losses in these production areas, but previous researches have not comprehensively investigated this issue. In this study, we collected 287 faba bean samples over three consecutive years from eight provinces/municipalities of China. We employed small RNA sequencing, RT-PCR, DNA sequencing, and phylogenetic analysis to detect the presence of viruses and examine their incidence, distribution, and genetic diversity. We identified a total of nine distinct viruses: bean yellow mosaic virus (BYMV, Potyvirus), milk vetch dwarf virus (MDV, Nanovirus), vicia cryptic virus (VCV, Alphapartitivirus), bean common mosaic virus (BCMV, Potyvirus), beet western yellows virus (BWYV, Polerovirus), broad bean wilt virus (BBWV, Fabavirus), soybean mosaic virus (SMV, Potyvirus), pea seed-borne mosaic virus (PSbMV, Potyvirus), and cucumber mosaic virus (CMV, Cucumovirus). BYMV was the predominant virus found during our sampling, followed by MDV and VCV. This study marks the first reported detection of BCMV in Chinese faba bean fields. Except for several isolates from Gansu and Yunnan provinces, our sequence analysis revealed that the majority of BYMV isolates contain highly conserved nucleotide sequences of coat protein (CP). Amino acid sequence alignment indicates that there is a conserved NAG motif at the N-terminal region of BYMV CP, which is considered important for aphid transmission. Our findings not only highlight the presence and diversity of pathogenic viruses in Chinese faba bean production, but also provide target pathogens for future antiviral resource screening and a basis for antiviral breeding.

Replacement of P1 of soybean mosaic virus with P1 of clover yellow vein virus has no impact on virus viability and host specificity

Potyvirus genomes are expressed as polyproteins that are autocatalytically cleaved to produce 10 to 12 multifunctional proteins, among which P1 is the most variable. It has long been hypothesized that P1 plays role(s) in host adaptation and host specificity. We tested this hypothesis using two phylogenetically distinct potyviruses: soybean mosaic virus (SMV), with a narrow host range, and clover yellow vein virus (ClYVV), with a broader host range. When the full-length P1 cistron of SMV-N was replaced with P1 from ClYVV-No.30, the chimera systemically infected only SMV-N-permissive hosts. Hence, there were no changes in the host range or host specificity of the chimeric viruses. Despite sharing only 20.3% amino acid sequence identity, predicted molecular models of P1 proteins from SMV-N and ClYVV-No.30 showed analogous topologies. These observations suggest that P1 of ClYVV-No.30 can functionally replace P1 of SMV-N. However, the P1 proteins of these two potyviruses are not determinants of host specificity and host range.

Whole-Genome Characterization of Alfalfa Mosaic Virus Obtained from Metagenomic Analysis of Vinca minor and Wisteria sinensis in Iran: with Implications for the Genetic Structure of the Virus

Alfalfa mosaic virus (AMV), an economically important pathogen, is present worldwide with a very wide host range. This work reports for the first time the infection of Vinca minor and Wisteria sinensis with AMV using RNA sequencing and reverse transcription polymerase chain reaction confirmation. De novo assembly and annotating of contigs revealed that RNA1, RNA2, and RNA3 genomic fragments consist of 3,690, 2,636, and 2,057 nucleotides (nt) for IR-VM and 3,690, 2,594, and 2,057 nt for IR-WS. RNA1 and RNA3 segments of IR-VM and IR-WS closely resembled those of the Chinese isolate HZ, with 99.23-99.26% and 98.04-98.09% nt identity, respectively. Their RNA2 resembled that of Canadian isolate CaM and American isolate OH-2-2017, with 97.96-98.07% nt identity. The P2 gene revealed more nucleotide diversity compared with other genes. Genes in the AMV genome were under dominant negative selection during evolution, and the P1 and coat protein (CP) proteins were subject to the strongest and weakest purifying selection, respectively. In the population genetic analysis based on the CP gene sequences, all 107 AMV isolates fell into two main clades (A, B) and isolates of clade A were further divided into three groups with significant subpopulation differentiation. The results indicated moderate genetic variation within and no clear geographic or genetic structure between the studied populations, implying moderate gene flow can play an important role in differentiation and distribution of genetic diversity among populations. Several factors have shaped the genetic structure and diversity of AMV: selection, recombination/reassortment, gene flow, and random processes such as founder effects.

Wisteria Vein Mosaic Virus Detected for the First Time in Iran from an Unknown Host by Analysis of Aphid Vectors

The development of reverse transcription-polymerase chain reaction using degenerate primers against conserved regions of most potyviral genomes enabled sampling of the potyvirome. However, these assays usually involve sampling potential host plants, but identifying infected plants when they are asymptomatic is challenging, and many plants, especially wild ones, contain inhibitors to DNA amplification. We used an alternative approach which utilized aphid vectors and indicator plants to identify potyviruses capable of infecting common bean (Phaseolus vulgaris). Aphids were collected from a range of asymptomatic leguminous weeds and trees in Iran, and transferred to bean seedlings under controlled conditions. Bean plants were tested serologically for potyvirus infections four-weeks post-inoculation. The serological assay and symptomatology together indicated the presence of one potyvirus, and symptomology alone implied the presence of an unidentified virus. The partial genome of the potyvirus, encompassing the complete coat protein gene, was amplified using generic potyvirus primers. Sequence analysis of the amplicon confirmed the presence of an isolate of Wisteria vein mosaic virus (WVMV), a virus species not previously identified from Western Asia. Phylogenetic analyses of available WVMV sequences categorized them into five groups: East Asian-1 to 3, North American and World. The Iranian isolate clustered with those in the World group. Multiple sequence alignment indicated the presence of some genogroup-specific amino acid substitutions among the isolates studied. Chinese isolates were sister groups of other isolates and showed higher nucleotide distances as compared with the others, suggesting a possible Eastern-Asian origin of WVMV, the main region where Wisteria might have originated.

Precise Exchange of the Helper-Component Proteinase Cistron Between Soybean mosaic virus and Clover yellow vein virus: Impact on Virus Viability and Host Range Specificity

Soybean mosaic virus and Clover yellow vein virus are two definite species of the genus Potyvirus within the family Potyviridae. Soybean mosaic virus-N (SMV-N) is well adapted to cultivated soybean (Glycine max) genotypes and wild soybean (G. soja), whereas it remains undetectable in inoculated broad bean (Vicia faba). In contrast, clover yellow vein virus No. 30 (ClYVV-No. 30) is capable of systemic infection in broad bean and wild soybean; however, it infects cultivated soybean genotypes only locally. In this study, SMV-N was shown to also infect broad bean locally; hence, broad bean is a host for SMV-N. Based on these observations, it was hypothesized that lack of systemic infection by SMV-N in broad bean and by ClYVV-No. 30 in cultivated soybean is attributable to the incompatibility of multifunctional helper-component proteinase (HC-Pro) in these hosts. The logic of selecting the HC-Pro cistron as a target is based on its established function in systemic movement and being a relevant factor in host range specificity of potyviruses. To test this hypothesis, chimeras were constructed with precise exchanges of HC-Pro cistrons between SMV-N and ClYVV-No. 30. Upon inoculation, both chimeras were viable in infection, but host range specificity of the recombinant viruses did not differ from those of the parental viruses. These observations suggest that (i) HC-Pro cistrons from SMV-N and ClYVV-No. 30 are functionally compatible in infection despite 55.6 and 48.9% nucleotide and amino acid sequence identity, respectively, and (ii) HC-Pro cistrons from SMV-N and ClYVV-No. 30 are not the determinants of host specificity on cultivated soybean or broad beans, respectively.

Applications of Next-Generation Sequencing for Large-Scale Pathogen Diagnoses in Soybean

Soybean (Glycine max) has become an important crop in Manitoba, Canada, with a 10-fold increase in dedicated acreage over the past decade. Given the rapid increase in production, scarce information about foliar diseases present in the province has been recorded. In order to describe the foliar pathogens affecting this legume, we harnessed next-generation sequencing (NGS) to carry out a comprehensive survey across Manitoba in 2016. Fields were sampled during the V2/3 (33 fields) and R6 (70 fields) growth stages, with at least three symptomatic leaves per field collected and subjected to RNA sequencing. We successfully detected several bacteria, fungi, and viruses known to infect soybean, including Pseudomonas savastanoi pv. glycinea, Septoria glycines, and Peronospora manshurica, as well as pathogens not previously identified in the province (e.g., Pseudomonas syringae pv. tabaci, Cercospora sojina, and Bean yellow mosaic virus). For some microorganisms, we were able to disentangle the different pathovars present and/or assemble their genome sequence. Since NGS generates data on the entire flora and fauna occupying a leaf sample, we also identified residual pathogens (i.e., pathogens of crops other than soybean) and multiple species of arthropod pests. Finally, the sequence information produced by NGS allowed for the development of polymerase chain reaction-based diagnostics for some of the most widespread and important pathogens. Although there are many benefits of using NGS for large-scale plant pathogen diagnoses, we also discuss some of the limitations of this technology.

Drivers of farmers' intention to use integrated pest management: Integrating theory of planned behavior and norm activation model

Integrated pest management (IPM) has been promoted as an environmentally friendly pest control approach, but its adoption by farmers, particularly in developing countries, is low. The main purpose of the current study was to examine factors affecting the intention of farmers to use IPM practices in Iran. The research model was developed using the Theory of Planned Behavior (TPB) and the Norm Activation Model (NAM) and was empirically tested using data obtained from structured interviews with 327 tomato producers in Zanjan Province in northwestern Iran. Structural Equation Modeling (SEM) analysis indicated that all three components of attitude, perceived behavioral control (PBC), and subjective norm significantly influenced intention in the original TPB, while subjective norm had no statistically significant effect on intention in the integrative TPB-NAM. Despite this fact, subjective norm significantly impacted attitude, PBC, and personal norm in the integrative model. The study also supported the significant effect of awareness of consequences (AC) on personal norm, ascription of responsibility (AR), attitude, and subjective norm as well as the significant effect of AR on personal norm. Overall, personal norm was the most salient determinant of farmers' intention to use IPM practices in the integrative model. Most notably, integrating the constructs of TPB and NAM and particularly adding the interrelationships among the volitional, moral, and cognitive dimensions of the two models significantly enhanced the predictive power, utility, and comprehensiveness of the proposed framework for explaining farmers' intention to use IPM practices. The findings of this research provide a clearer understanding of factors driving the promotion of IPM among farming community and can be a basis for developing IPM policy interventions in Iran and other developing countries.

Transcriptomic signature reveals mechanism of flower bud distortion in witches'-broom disease of soybean (Glycine max)

BACKGROUND

Soybean (Glycine max L. Merril) crop is major source of edible oil and protein for human and animals besides its various industrial uses including biofuels. Phytoplasma induced floral bud distortion syndrome (FBD), also known as witches' broom syndrome (WBS) has been one of the major biotic stresses adversely affecting its productivity. Transcriptomic approach can be used for knowledge discovery of this disease manifestation by morpho-physiological key pathways.

RESULTS

We report transcriptomic study using Illumina HiSeq NGS data of FBD in soybean, revealing 17,454 differentially expressed genes, 5561 transcription factors, 139 pathways and 176,029 genic region putative markers single sequence repeats, single nucleotide polymorphism and Insertion Deletion. Roles of PmbA, Zn-dependent protease, SAP family and auxin responsive system are described revealing mechanism of flower bud distortion having abnormalities in pollen, stigma development. Validation of 10 randomly selected genes was done by qPCR. Our findings describe the basic mechanism of FBD disease, right from sensing of phytoplasma infection by host plant triggering molecular signalling leading to mobilization of carbohydrate and protein, phyllody, abnormal pollen development, improved colonization of insect in host plants to spread the disease. Study reveals how phytoplasma hijacks metabolic machinery of soybean manifesting FBD.

CONCLUSIONS

This is the first report of transcriptomic signature of FBD or WBS disease of soybean revealing morphological and metabolic changes which attracts insect for spread of disease. All the genic region putative markers may be used as genomic resource for variety improvement and new agro-chemical development for disease control to enhance soybean productivity.

A New Distinct Clade for Iranian Tomato spotted wilt virus Isolates Based on the Polymerase, Nucleocapsid, and Non-structural Genes

Tomato spotted wilt virus (TSWV; Genus Orthotospovirus: Family Tospoviridae) is one of the most destructive viruses affecting a wide range of horticultural crops on a worldwide basis. In 2015 and 2016, 171 leaf and fruit samples from tomato (Solanum lycopersicum) plants with viral symptoms were collected from the fields in various regions of Iran. ELISA test revealed that the samples were infected by TSWV. The results of RT-PCR showed that the expected DNA fragments of about 819 bp in length were amplified using a pair of universal primer corresponding to the RNA polymerase gene and DNA fragments of ca 777 bp and 724 bp in length were amplified using specific primers that have been designed based on the nucleocapsid (N) and non-structural (NSs) genes, respectively. The amplified fragments were cloned into pTG19-T and sequenced. Sequence comparisons with those available in the GenBank showed that the sequences belong to TSWV. The high nucleotide identity and similarities of new sequences based on the L, N, and NSs genes showed that minor evolutionary differences exist amongst the isolates. The phylogenetic tree grouped all isolates six clades based on N and NSs genes. Phylogenetic analysis showed that the Iranian isolates were composed a new distinct clade based on a part of polymerase, N and NSs genes. To our knowledge, this is the first detailed study on molecular characterization and genetic diversity of TSWV isolates from tomato in Iran that could be known as new clade of TSWV isolates.

Characterization and Genetic Structure of a Tospovirus Causing Chlorotic Ring Spots and Chlorosis Disease on Peanut; Comparison with Iranian and Polish Populations of Tomato yellow fruit ring virus

A Tospovirus species was isolated from peanut plants showing chlorotic ring spots and chlorosis, and identified as Tomato yellow fruit ring virus (TYFRV) on the basis of its biological, serological, and molecular properties. In host range studies, a broad range of indicator plants was infected by the five isolates studied; all the isolates systemically infected Nicotiana tabacum cultivars and, thus, they were classified into the N-host-infecting type isolates of the virus. These isolates strongly reacted with TYFRV antibodies but not with the specific antibodies of other tospoviruses tested. Recombination analyses showed that the nucleoprotein gene of the peanut isolates and other isolates studied were nonrecombinant. In phylogenetic trees, the virus isolates were clustered in three genogroups: IRN-1, IRN-2, and a new group, POL; the peanut isolates fell into IRN-2 group. Multiple sequence alignments showed some genogroup-specific amino acid substitutions among the virus isolates studied. The results revealed the presence of negative selection in TYFRV populations. Also, the Iranian populations had higher nucleotide diversity compared with the Polish population. Genetic differentiation and gene flow analyses indicated that the populations from Iran and Poland and those belonging to different genogroups were partially differentiated populations. Our findings seem to suggest that there has been frequent gene flow between some populations of the virus in the mid-Eurasian region of Iran.

Cytological behaviour of floral organs and in silico characterization of differentially expressed transcript-derived fragments associated with 'floral bud distortion' in soybean

An attempt was made to understand the 'floral bud distortion' (FBD), an unexplored disorder prevailing in soybean. Cytological behaviour of floral reproductive organs and in silico characterization of differentially expressed transcript-derived fragments (TDFs) in symptomatic and asymptomatic soybean plants were carried out. Pollens in asymptomatic plants do not have defects in number, size, shape and function. However, in symptomatic plant, pollens were found nonviable, abnormal in shape and with reduced germination ability. Here, we employed a computational approach, exploring invaluable resources. The tissue-specific transcript profile of symptomatic and asymptomatic sources was compared to determine differentially expressed TDFs associated with FBD to improve its basic understanding. A total of 60 decamer primers produced 197 scorable amplicons, ranged 162-1130 bp, of which 171 were monomorphic and 26 were differentially regulated. Reproducible TDFs were sequenced and characterized for their homology analysis, annotation, protein-protein interaction, subcellular localization and their physical mapping. Homology-based annotation of TDFs in soybean revealed presence of two characterized and seven uncharacterized hits. Annotation of characterized sequences showed presence of genes, namely auxin response factor 9 (ARF9) and forkhead-associated (FHA) domain, which are directly involved in plant development through various pathways, such as hormonal regulation, plant morphology, embryogenesis and DNA repair.

Partial biological and molecular characterization of a Cucumber mosaic virus isolate naturally infecting Cucumis melo in Iran

Melon seedlings showing systemic chlorotic spots and mosaic symptoms were collected in central part of Iran, and a virus was isolated from diseased plants by mechanical inoculation. The virus systemically infected the most inoculated test plants by inducing mosaic symptoms, while, in the members of Fabaceae family and Chenopodium quinoa induced local lesions. Agar gel diffusion test using a polyclonal antiserum against a squash Cucumber mosaic virus (CMV) isolate showed the presence of CMV in the mechanically inoculated plants (designated CMV-Me). The virus was purified by polyethylene glycol precipitation and differential centrifugation. A polyclonal antiserum was produced against the virus that reacted specifically with virus antigen in ELISA and agar gel diffusion tests. The virus was molecularly characterized by PCR amplification of the full length of the coat protein gene using cucumovirus genus specific primer pair CPTALL-3/CPTALL-5 and sequence analysis of the resulting product. No RNA satellite was detected using the primer pair CMVsat3H/sat5T7P. Phylogenetic analysis based on the coat protein amino acid sequences showed that CMV-Me belongs to Subgroup IB. These results may be helpful in melon breeding programs, focusing on plant resistance to plant viruses including CMV.

Incidence of Viruses Infecting Tomato and Their Natural Hosts in the Southeast and Central Regions of Iran

A survey was conducted to determine the incidence of Cucumber mosaic virus (CMV), Beet curly top virus (BCTV), Tomato yellow leaf curl virus (TYLCV), Tomato chlorotic spot virus (TcSV), Potato virus Y (PVY), Potato virus S (PVS), Tomato spotted wilt virus (TSWV), Tomato ringspot virus (TRSV), Tomato aspermy virus (TAV), Arabis mosaic virus (ArMV), Tobacco streak virus (TSV), Tomato bushy stunt virus (TBSV), Tobacco mosaic virus (TMV), and Tomato mosaic virus (ToMV) on tomato (Solanum lycopersicum) in the major horticultural crop growing areas in the southeast and central regions of Iran. A total of 1,307 symptomatic leaf samples from fields and 603 samples from greenhouses were collected from January 2003 to July 2005 in five southeastern and central provinces of Iran. Samples of symptomatic plants were analyzed for virus infection by enzyme-linked immunosorbent assay (ELISA) using specific polyclonal antibodies. ArMV and CMV were the most frequently found viruses, accounting for 25.6 and 23.4%, respectively, of the collected samples. BCTV, TSWV, TMV, PVY, ToMV, and TYLCV were detected in 6.1, 5.8, 5.6, 5, 4.8, and 1.6% of the samples, respectively. TBSV, TAV, TSV, PVS, and TRSV were not detected in any of the samples tested. Double and triple infections involving different combination of viruses were found in 13.9 and 1.7% of samples, respectively. This is the first report of PVY and ArMV as viruses naturally infecting tomato in Iran. Infection of tomato plants with PVY and ArMV was confirmed. Six out of 20 plant species belonging to six genera, growing in tomato fields or in the nearby areas, were found infected with TSWV, TMV, PVY, and CMV.

Detection and some properties of cowpea mild mottle virus isolated from soybean in Iran

During 2006-2007 growing seasons, survey were carried to identify a virus disease causing mosaic of soybean in the field in Southern region (Khozestan Province) of Iran. To detect the viral infection, diseased leaf samples showing mild mosaic and leaf malformation were collected from soybean fields in Dezful, located in Khozestan Province. Infected samples were carried to the lab in a proper condition on ice packages. TPIA and DAS-ELISA serological tests were applied to identify the viral agent. To investigate the host-range, several indicator plants were mechanically inoculated under green-house condition. Seed transmission of CPMMV was examined using the seeds obtained from infected plants. The virus isolate was not found to be seed-borne in Clark variety of soybean. Different steps of ultracentrifugation including sucrose density gradient (10-40%) were carried out in order to obtain partial purified virus. On the basis of biological, serological and EM results, CPMMV-Carla virus was identified in the infected soybean samples. This is the first report of CPMMV infection of soybean in Iran.

Detection and Characterization of a Distinct Isolate of Tomato yellow fruit ring virus from Potato

A distinct isolate (TY-PF36) of Tomato yellow fruit ring virus (TYFRV) was obtained from potato (Solanum tuberosum) in Iran. Chlorosis and necrotic spots on leaves associated with leaf and stem necrosis symptoms appear on the affected plants. Of 32 plant species and cultivars mechanically inoculated, 24 were susceptible to the virus isolate. The isolate strongly reacted with TYFRV antibodies in enzyme-linked immunosorbent assay (ELISA), but not with the specific antibodies of other tospoviruses tested. TYFRV-specific N gene primers described previously, however, failed to produce DNA fragments from the total RNA extracts of the infected plants in reverse transcription-polymerase chain reaction (RT-PCR). Nucleotide sequencing of the complete N gene and partial L gene of this isolate revealed considerable differences to those reported for TYFRV with identities ranging from 83.9 to 84.2% and 84.9 to 85.4%, respectively. Two specific primers were designed for detecting TY-PF36 using RT-PCR; TY-PF36 was detected in symptomatic field samples of potato, peanut, soybean, and two weed species, Datura metel and D. stramonium.

Incidence and Distribution of Important Viral Pathogens in Some Iranian Potato Fields

From a total of 8,135 potato leaves collected from 132 fields in 11 provinces of Iran, the incidence and distribution of Alfalfa mosaic virus (AlMV), Eggplant mottled dwarf virus (EMDV), Potato leafroll virus (PLRV), Potato virus A (PVA), Potato virus M (PVM), Potato virus S(PVS), Potato virus X (PVX), Potato virus Y (PVY), and Tomato yellow fruit ring virus (TYFRV) were assessed using serological and biological methods. Based on enzyme-linked immunosorbent assay (ELISA) results, viruses in decreasing order of incidence in potato were PVS (35.9%), PVY (34.4%), PVA (27.0%), PVX (20.8%), PLRV (13.9%), PVM (9.0%), AlMV (7.0%), TYFRV (5.9%), and EMDV (5.1%). All 132 fields surveyed had some degree of virus infection, ranging from 28.8 to 98.6%, with an overall incidence of 75.2%. The highest and lowest incidence of virus infections among the surveyed provinces occurred in Kerman (93.2%) and Ardabil (56.7%), respectively. Overall, 25.0 and 50.2% of the collected potato samples had single or mixed infections, respectively. High levels of mixed infections were found between PVX and PVS (8.6%), and PVX and PVY (7.6%). Moreover, co-infection of samples with PVS and PVY, PVA and PVS, and PVA and PVY, the aphid-vectored virus/virus combinations, occurred at the highest incidence in almost all provinces surveyed, 15.3, 13.8, and 12.8%, respectively. In this study, Beet curly top virus was detected in symptomatic potato samples collected from some fields in the Kermanshah province.

Molecular and biological comparison of two Tomato yellow ring virus (TYRV) isolates: challenging the Tospovirus species concept

Two strains of Tomato yellow ring virus (TYRV, genus Tospovirus), one from tomato (referred to as TYRV-t) and the other from soybean and potato (denoted TYRV-s), collected from different geographical regions in Iran, were compared. Their genomic S RNA segments differed in size by 55 nucleotides. Comparison of the S RNA intergenic regions revealed the absence of a stretch of 115 nucleotides within the S RNA segment of TYRV-s and, conversely, of 56 nts in that of TYRV-t, apparently a stable genetic difference as it was also found in another isolate of TYRV-s collected from potato. Sequence comparison of the N protein ORFs revealed an identity of 92% between the N proteins of both strains, and the observed strong cross-reaction of TYRV-s in DAS-ELISA with a polyclonal antiserum directed against the TYRV-t N protein confirmed this high identity. Host range analysis revealed several differences, e.g. TYRV-s, but not TYRV-t, being able to systemically infect Nicotiana species, and TYRV-s being localised in tomato. The observed molecular and biological differences of both viruses call into question the currently used criteria for Tospovirus species demarcation.

Distribution and Incidence of Some Aphid and Leafhopper Transmitted Viruses Infecting Sugar Beets in Iran

The main areas for field-grown sugar beet (Beta vulgaris) production in Iran were surveyed to study the occurrence and incidence of Alfalfa mosaic virus (AlMV), Beet curly top virus (BCTV), Beet mosaic virus (BtMV), Beet western yellows virus (BWYV), Beet yellows virus (BYV), Chickpea chlorotic dwarf virus (CpCDV), Cucumber mosaic virus (CMV), and Turnip mosaic virus (TuMV) during the growing season of 2001. A total of 5,292 random leaf samples in addition to 1,294 symptomatic leaves were collected from nine commercial sugar beet growing provinces of Iran and tested by tissue-blot immunoassay (TBIA). Serological diagnoses were confirmed by electron microscopy and host range studies. The highest virus incidence among the surveyed provinces was recorded in Qazvin, followed by Fars, Esfahan, Azarbayejan-e-gharbi, Khorasan, Kermanshah, Semnan, and Hamedan. According to the TBIA results, viruses in decreasing order of incidence in sugar beet were BCTV (27.9%), followed by BWYV (17.4%), CpCDV (12.5%), BYV (10.6%), BtMV (7.4%), TuMV (2.9%), AlMV (1.3%), and CMV (1.2%). Nearly 35% of sugar beets in Iran were infected by one or both of the two leafhopper-transmitted viruses (BCTV and CpCDV). Moreover, about 28% were infected by at least one of the six aphid-transmitted viruses (AlMV, BWYV, BtMV, BYV, CMV, and TuMV). Overall, one or more of the eight viruses assayed were detected in 45.5% of the plants surveyed. Several plants (35%) displaying virus-like symptoms did not react with the virus antisera used, suggesting that more viruses or virus-like agents are infecting sugar beets in Iran. In reference to the earlier reports, this is the first report of AlMV and TuMV in sugar beet fields of Iran. Also, this is the first detection of CpCDV as a pathogen of sugar beet.