Wheat Streak Research Articles

Genomic High Plains Wheat Mosaic Virus Sequences from Australia: Their Phylogenetics and Evidence for Emaravirus Recombination and Reassortment.

High Plains wheat mosaic virus (HPWMoV) causes a serious disease in major wheat-growing regions worldwide. We report here the complete or partial genomic sequences of five HPWMoV isolates from Australian wheat samples. Phylogenetic analysis of the nucleotide sequences of the eight genomic segments of these five isolates together with others from Genbank found all eight genes formed two lineages, L1 and L2. L1 contained a single isolate from Colorado in the North American Great Plains Region (GPR), and L2 had two unresolved clusters, A and B, of isolates from Australia and the GPR. A quarter of the L2B isolate sequences of the nucleocapsid gene (RNA3) were recombinant, which is unexpected as little evidence of recombination exists in viruses with negative single-stranded RNA genomes. Phylogenies calculated from the amino acid sequences of HPWMoV's RNA-dependent RNA-polymerase (RNA1), glycoprotein (RNA2), and nucleocapsid protein (RNA3) showed they were closest to those of Palo Verde broom virus. However, its movement protein (RNA4) was closer to those of Ti ringspot-associated and common oak ringspot-associated viruses, indicating the RNA4 segments of their ancestors reassorted to produce the current emaraviruses. To avoid increased yield losses from co-infection, biosecurity measures are advised to avoid HPWMoV introduction to countries where wheat streak mosaic virus already occurs.

Agronomic and quality impact of a shortened translocation for wheat streak mosaic virus resistance

AbstractWheat streak mosaic virus (WSMV) is a mite‐vectored virus with substantial economic impact on wheat production. One of the effective sources of resistance to WSMV, Wsm1, is carried on a translocation from Thinopyrum intermedium. The original whole arm form of this translocation (T4DL·4JsS) was highly effective against WSMV but carried a substantial yield penalty in the absence of the virus. Shorter recombinants of the Th. intermedium translocation are now available. This study characterized the agronomic performance of near‐isogenic sib‐pair families in 10 yield trials using one of these shortened T4DL·4DS‐4JsS translocations, named “rec213,” in the absence of visible disease. This translocation had no effect on heading date, was associated with a modest reduction (≤ 4.8 cm) in plant height, and the translocation had a favorable effect (≤ 12.6%) on grain yield in those environments where highly significant genotype effects were detected. The translocation did not affect protein concentration or lactic acid‐sodium dodecyl sulfate solvent retention capacity, a measure of gluten quality. However, families with the translocation had slightly (≤ 5%) lower protein quality scores than paired families without the translocation. We do not expect this modest difference in quality to be a barrier to utilization of the rec213 translocation for Wsm1, but we encourage breeders to work within high‐quality genetic backgrounds when using the rec213 translocation and to monitor the quality of breeding selections. Improved codominant PCR‐based marker assays were developed to facilitate the use of the rec213 Wsm1 trait in breeding programs.

Comparative profiling of volatile organic compounds associated to temperature sensitive resistance to wheat streak mosaic virus (WSMV) in resistant and susceptible wheat cultivars at normal and elevated temperatures

To investigate changes in wheat resistance to wheat streak mosaic virus (WSMV) at normal and elevated temperatures and their effects on the emission of volatile organic compounds (VOCs), the profile of these compounds in WSMV-resistant (R) and susceptible (S) wheat cultivars were analyzed. VOCs were discovered in leaves of R and S cultivars inoculated to WSMV at 20 °C and 32 °C at 24, 48 and 72 h post inoculation (hpi) by GC. MS–HS–SPME. Many VOCs and related metabolic pathways of WSMV inoculated and control plants responded differently at low/high temperatures in R/S cultivars. Compounds such as 6-methyl-5-hepten-2-one and heptanal, represented the maximum abundance in R plants compared to S plants at earlier times especially, 48 hpi/20 °C. Also, at 32 °C, VOCs including heptanal and 2-pentenal had the highest increase in abundance at a later time. In addition, in R plants, several pathways were up-regulated commonly at 20 °C and 32 °C. Although, at 20 °C, they were activated at an earlier time. At 32 °C, most of these pathways were up-regulated at 72 hpi. The most important pathways correlated to combined stresses included lipoxygenase, cuticular wax biosynthesis, fatty acid and lipid biosynthesis. The pathway of phenyl ethanol biosynthesis was up-regulated only at 32 °C, which probably is specifically related to resistance to heat stress. Up-regulation of the lipoxygenase pathway appears to increase vector attractiveness and tolerance to biotic and abiotic stresses. Based on these results, is suggested that there is a particular synchronized regulation of defense-related multi-dimensional VOCs emitting network that is necessary for the occurrence of wheat defense responses against WSMV and/or heat. This research highlights the challenge of global warming and the breakdown of plant resistance to viruses which requires metabolic engineering of VOCs for sustainable agriculture.

Confirmatory detection and identification of biotic and abiotic stresses in wheat using Raman spectroscopy.

Wheat is one of the oldest and most widely cultivated staple food crops worldwide. Wheat encounters an array of biotic and abiotic stresses during its growth that significantly impact the crop yield and consequently global food security. Molecular and imaging methods that can be used to detect such stresses are laborious and have numerous limitations. This catalyzes the search for alternative techniques that can be used to monitor plant health. Raman spectroscopy (RS) is a modern analytical technique that is capable of probing structure and composition of samples non-invasively and non-destructively. In this study, we investigate the accuracy of RS in confirmatory diagnostics of biotic and abiotic stresses in wheat. Specifically, we modelled nitrogen deficiency (ND) and drought, key abiotic stresses, and Russian wheat aphid (Diuraphis noxia) infestation and viral diseases: wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV), economically significant biotic stresses in common bread wheat. Raman spectra as well as high pressure liquid chromatography (HPLC)-based analyses revealed drastically distinct changes in the intensity of carotenoid vibration (1185 cm-1) and in the concentration of lutein, chlorophyll, and pheophytin biomolecules of wheat, triggered in response to aforementioned biotic and abiotic stresses. The biochemical changes were reflected in unique vibrational signatures in the corresponding Raman spectra, which, in turn could be used for ~100% accurate identification of biotic and abiotic stresses in wheat. These results demonstrate that a hand-held Raman spectrometer could provide an efficient, scalable, and accurate diagnosis of both biotic as well as abiotic stresses in the field.

Wheat Curl Mite: A New Source of the Eriophyoid Mite in Wheat Fields Identified

Wheat curl mites (WCMs; Aceria tosichella) are an important global pest of cultivated wheat. Their feeding activities on epidermal cells of wheat leaves result in characteristic leaf curl symptoms that prevent the unfurling of affected leaves and impair the proper emergence of heads from the boot stage. The most significant economic impact of WCM infestation, however, is their ability to vector and transmit four important viruses of wheat, specifically, wheat streak mosaic virus, Triticum mosaic virus, High Plains wheat mosaic emaravirus, and brome streak mosaic virus. Being wingless, WCMs are almost completely dependent on air currents for their dispersal. In addition, because of their obligate lifestyle, wheat field infestations are thought to originate from sources such as volunteer wheat. Corn and other cultivated and noncultivated Poaceae hosts are also known to act as green bridges between successive wheat crops. Consequently, management practices mostly target these off-season host plants but also the use of resistant varieties and other cultural control methods. Here we report the discovery of seed-borne WCM eggs, a previously unknown method of their dispersal, as a possible source of new infestations in wheat fields. This discovery expands our understanding of the biology of WCMs, with potential implications for the development of more holistic and effective management strategies for this economic pest and virus vector. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Occurrence of Wheat Curl Mite and Mite-Vectored Viruses of Wheat in Colorado and Insights into the Wheat Virome.

The wheat curl mite (WCM) is a vector of three important wheat viruses in the U.S. Great Plains: wheat streak mosaic virus (WSMV), triticum mosaic virus (TriMV), and High Plains wheat mosaic virus (HPWMoV). This study was conducted to determine the current profile of WCM and WCM-transmitted viruses of wheat and their occurrence in Colorado, including novel wheat viruses via virome analysis. There was a high rate of virus incidence in symptomatic wheat samples collected in 2019 (95%) and 2020 (77%). Single infection of WSMV was most common in both years, followed by coinfection with WSMV + TriMV and WSMV + HPWMoV. Both type 1 and type 2 mite genotypes were found in Colorado. There was high genetic diversity of WSMV and HPWMoV isolates, whereas TriMV isolates showed minimal sequence variation. Analysis of WSMV isolates revealed novel virus variants, including one isolate from a variety trial, where severe disease symptoms were observed on wheat varieties carrying Wsm2, a known virus resistance locus. Virome analysis identified two to four sequence variants of all eight RNA segments of HPWMoV, which suggests co-occurrence of multiple genotypes within host populations and presence of a variant of HPWMoV. A possible novel virus in the family Tombusviridae and several mycoviruses were identified. Overall, the data presented here highlight the need to define the effect of novel WCM-transmitted virus variants on disease severity and the role of novel viruses.

Phylogenetics and evolution of wheat streak mosaic virus: Its global origin and the source of the Australian epidemic

AbstractWheat streak mosaic tritimovirus (WSMV) seriously damages wheat worldwide. We report analyses of new complete ORF (CO) sequences from seven Australian isolates with 56 COs and 128 coat protein (CP) genes sequenced previously. Eleven CO and three CP sequences were recombinants so were removed from our analyses. Patristic distances of maximum‐likelihood phylogenies of nonrecombinant (n‐rec) CO sequences and their CP sequences were closely correlated (R = 0.994, p ≤ 0.00001). The phylogeny of all 188 n‐rec CP genes had four well‐supported phylogroups (I–IV): phylogroup I (one Mexican sequence), phylogroup II (six Iranian sequences), phylogroup III (48 sequences) and phylogroup IV (133 sequences), each with basal Iranian sequences and either mostly European (phylogroup III) or mostly American (phylogroup IV) terminal sequences. Australian and South American sequences formed a phylogroup IV subcluster within a Pacific Northwest USA cluster. Unlike the Iranian, South American and European populations, the North American and Australian populations demonstrated recent population imbalance. Sample collection dates of 40 CO sequences are known, allowing WSMV phylogeny dating by RTDT methodology. The most recent WSMV ancestor was dated at 1456 CE, and the Australian cluster at 1998.7 CE, only 2–3 years before WSMV was first reported. Tritimoviruses originated in central Eurasia, WSMV first entering wheat in its Middle East domestication centre and one basal lineage being taken to Mexico after the Spanish conquest, whereas the other most basal lineage spread throughout Iran, before spreading to other world regions. Probable future spread to other world regions of additional WSMV phylogroups, and of interphylogroup recombinants, constitutes a biosecurity concern.

Genomic and Molecular Characterization of Wheat Streak Mosaic Virus Resistance Locus 2 (Wsm2) in Common Wheat (Triticum aestivum L.).

Wheat streak mosaic virus (WSMV) is an economically important viral pathogen that threatens global wheat production, particularly in the Great Plains of the United States. The Wsm2 locus confers resistance to WSMV and has been widely deployed in common wheat varieties adapted to this region. Characterizing the underlying causative genetic variant would contribute to our understanding of viral resistance mechanisms in wheat and aid the development of perfect markers for breeding. In this study, linkage mapping in a doubled-haploid (DH) mapping population confirmed Wsm2 as a major locus conferring WSMV resistance in wheat. The Wsm2 flanking markers were mapped to a 4.0 Mbp region at the distal end of chromosome 3BS containing 142 candidate genes. Eight haplotypes were identified from seventeen wheat genotypes collected from different agroecological zones, indicating that Wsm2 lies in a dynamic region of the genome with extensive structural variation and that it is likely a rare allele in most available genome assemblies of common wheat varieties. Exome sequencing of the variety “Snowmass”, which carries Wsm2, revealed several loss-of-function mutations and copy number variants in the 142 candidate genes within the Wsm2 interval. Six of these genes are differentially expressed in “Snowmass” compared to “Antero,” a variety lacking Wsm2, including a gene that encodes a nucleotide-binding site leucine-rich repeat (NBS-LRR) type protein with homology to RPM1. A de novo assembly of unmapped RNA-seq reads identified nine transcripts expressed only in “Snowmass,” three of which are also induced in response to WSMV inoculation. This study sheds light on the variation underlying Wsm2 and provides a list of candidate genes for subsequent validation.

Occurrence and Characterization of Wheat Streak Mosaic Virus Found in Mono- and Mixed Infection with High Plains Wheat Mosaic Virus in Winter Wheat in Ukraine.

Although wheat streak mosaic virus (WSMV) is a well-known pathogen inducing significant crop losses and endangering wheat production worldwide, the recent discovery of High Plains wheat mosaic virus (HPWMoV) in Ukraine raises questions on the co-existence of these two viruses having a similar host range and the same mite vector. Here we report on the screening of winter wheat industrial plantings in several important regions of Ukraine for WSMV and HPWMoV. WSMV was identified in an extremely high number of symptomatic plants (>85%) as compared to HPWMoV detected in 40% of wheat samples. Importantly, the preferred mode of HPWMoV circulation in Ukraine was mixed infection with WSMV (>30%) as opposed to WSMV, which was typically found in monoinfection (60%). Screening wheat varieties for possible virus resistance indicated that all but one were susceptible to WSMV, whereas over 50% of the same varieties were not naturally infected with HPWMoV. Overall, phylogenetic analysis of the collected WSMV and HPWMoV isolates indicated their high identity and similarity to other known isolates of the respective viruses. Here we first characterize WSMV isolates found in winter wheat plants in mono- or mixed infection with HPWMoV, which was recently reported as a typical wheat pathogen in Ukraine.

A reproducible methodology for absolute viral quantification and viability determination in mechanical inoculations of wheat streak mosaic virus

Wheat streak mosaic virus (WSMV) is a common wheat virus causing economic losses to production in the Great Plains of North America. Reproducible inoculation of WSMV by mechanical methods is essential to evaluate the resistance in breeding lines and relies on successful inoculation and infectivity of the virus particles. We used reverse transcription-quantitative PCR (RT-qPCR) for absolute quantification of viral genome copy numbers in both WSMV inoculum and in infected wheat leaves. A time-course study was designed to determine the viability of WSMV in inoculum over time as well as the copy number related to the phenotypic rating scale. In the phosphate inoculation buffer, WSMV was stable with average viral genome copy number 1.86 × 106 ± 4.85 × 105. Plants inoculated with this inoculation buffer using finger rub mechanical inoculation contained WSMV genome copy numbers in the infected leaves ranging between 2.66 × 104 and 4.69 × 106 at 21 to 28 days post-inoculation. Viral copy numbers were statistically similar between leaves inoculated immediately and those inoculated at later time points. There was a weak linear relationship between phenotypic rating score and copy number in infected leaves with the linear model explaining 40% of the variability (R2 = 0.40) indicating the difficulty in disease assessment based solely on phenotypic symptoms. This work describes an accurate methodology to quantify virus concentration in the inoculum and infected plants, as well as emphasizes the demand for absolute measurement of virus load to validate the subjective assessment for unbiased viral disease assessment.

Differential Synergistic Interactions Among Four Different Wheat-Infecting Viruses.

Field-grown wheat (Triticum aestivum L.) plants can be co-infected by multiple viruses, including wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), brome mosaic virus (BMV), and barley stripe mosaic virus (BSMV). These viruses belong to four different genera in three different families and are, hence, genetically divergent. However, the impact of potential co-infections with two, three, or all four of them on the viruses themselves, as well as the wheat host, has yet to be examined. This study examined bi-, tri-, and quadripartite interactions among these viruses in wheat for disease development and accumulation of viral genomic RNAs, in comparison with single virus infections. Co-infection of wheat by BMV and BSMV resulted in BMV-like symptoms with a drastic reduction in BSMV genomic RNA copies and coat protein accumulation, suggesting an antagonism-like effect exerted by BMV toward BSMV. However, co-infection of either BMV or BSMV with WSMV or TriMV led to more severe disease than singly infected wheat, but with a decrease or no significant change in titers of interacting viruses in the presence of BMV or BSMV, respectively. These results were in stark contrast with exacerbated disease phenotype accompanied with enhanced virus titers caused by WSMV and TriMV co-infection. Co-infection of wheat by WSMV, TriMV, and BMV or BSMV resulted in enhanced synergistic disease accompanied by increased accumulation of TriMV and BMV but not WSMV or BSMV. Quadripartite interactions in co-infected wheat by all four viruses resulted in very severe disease synergism, leading to the death of the most infected plants, but paradoxically, a drastic reduction in BSMV titer. Our results indicate that interactions among different viruses infecting the same plant host are more complex than previously thought, do not always entail increases in virus titers, and likely involve multiple mechanisms. These findings lay the foundation for additional mechanistic dissections of synergistic interactions among unrelated plant viruses.

Wheat streak mosaic virus (wheat streak)

Wheat streak mosaic virus (wheat streak)

ЗАХВОРЮВАНІСТЬ ТА ПОШИРЕННЯ ВІРУСІВ ЗЛАКОВИХ КУЛЬТУР У 2020–2021 РОКАХ В УКРАЇНІ

Cereals play a significant role in the Ukrainian economy and agriculture. Viral diseases can cause a serious reduction in yields. Aim. The aim of the work was to identify and determine the spread of grain viruses in the main cereal-growing regions of Ukraine in the period 2020–2021 using different methods of virus detection. Methods. Enzyme-linked immunosorbent assay was used to identify viruses using commercial test systems by for wheat streak mosaic virus (WSMV), barley stripe mosaic virus (BSMV), brome mosaic virus (BMV), wheat dwarf virus (WDV), High Plainswheat mosaic virus (HPWMoV), barley yellow dwarf virus-PAV (BYDV-PAV), barley yellow dwarf virus-MAV (BYDV-MAV), andcereal yellow dwarf virus-RPV (CYDV-RPV). Transmission electron microscopy was used for direct virus detection. Reverse transcription polymerase chain reaction was performed to identify viruses by molecular methods. Results. Summarizing the results obtained by different methods, we can say about the circulation of WSMV, HPWMoV, BSMV, BYDV-PAV, and BYDV-MAV in the Ukrainian agrocoenoses in 2020–2021. Significant prevalence and the dominant role of WSMV have been shown, with the degree of damage to symptomatic plants reaching 52 %. The spread of HPWMoV in Kyiv and Poltava regions has been established, although previously the virus was detected only in the eastern part of our country. WSMV was more likely to induce monoinfection (70 %). Conclusions. During the testing of symptomatic plants in the agrocenoses of Ukraine in 2020–2021 the most common were WSMV and HPWMoV (52 % and 19 %, respectively), also found BYDV-PAV in winter wheat and BYDV-MAV in oats.

Reactions of Winter Wheat, Spring Wheat, and Barley Cultivars to Mechanical Inoculation with Wheat Streak Mosaic Virus

Wheat streak mosaic virus (WSMV) causes sporadic epidemics in Montana, which can threaten profitability of the state’s small grains production. One challenge for WSMV management in Montana is that most commercially available wheat and barley cultivars are susceptible to WSMV or their performance under WSMV pressure is unknown. In a 3-year field study from 2017 to 2019 winter wheat, spring wheat, and barley cultivars were evaluated for their susceptibility to WSMV and yield performance under WSMV pressure. Plants were mechanically inoculated, and WSMV incidence was assessed using double antibody sandwich ELISA. There was effective resistance to WSMV in breeding line CO12D922, which had consistently low WSMV incidence, highlighting promising efforts in the development of WSMV-resistant winter wheat cultivars. Moderate WSMV incidence and minor yield losses were observed from WSMV infection of commercial winter wheat ‘Brawl CL Plus’ and Montana State University breeding line MTV1681. Spring wheat cultivars in this study had high WSMV incidence of up to 100% in ‘Duclair,’ ‘Egan,’ and ‘McNeal.’ High WSMV incidence was associated with severe yield losses as high as 85% for Duclair and ‘WB9879CLP’ in 2019, demonstrating a high degree of susceptibility to WSMV inoculation. Barley cultivars had considerably lower WSMV incidence compared with spring and winter wheat. Grain yield response to WSMV inoculation was variable between barley cultivars. The study provided an experimental basis for cultivar recommendations for high WSMV pressure environments and identified breeding lines and cultivars with potential resistance traits of interest to breeding programs that aim to develop WSMV-resistant cultivars.

Metagenomics Analysis of the Wheat Virome Identifies Novel Plant and Fungal-Associated Viral Sequences.

Wheat viruses including wheat streak mosaic virus, Triticum mosaic virus, and barley yellow dwarf virus cost substantial losses in crop yields every year. Although there have been extensive studies conducted on these known wheat viruses, currently, there is limited knowledge about all components of the wheat (Triticum aestivum L.) virome. Here, we determined the composition of the wheat virome through total RNA deep sequencing of field-collected leaf samples. Sequences were de novo assembled after removing the host reads, and BLASTx searches were conducted. In addition to the documented wheat viruses, novel plant and fungal-associated viral sequences were identified. We obtained the full genome sequence of the first umbra-like associated RNA virus tentatively named wheat umbra-like virus in cereals. Moreover, a novel bi-segmented putative virus tentatively named wheat-associated vipovirus sharing low but significant similarity with both plant and fungal-associated viruses was identified. Additionally, a new putative fungal-associated tobamo-like virus and novel putative Mitovirus were discovered in wheat samples. The discovery and characterization of novel viral sequences associated with wheat is important to determine if these putative viruses may pose a threat to the wheat industry or have the potential to be used as new biological control agents for wheat pathogens either as wild-type or recombinant viruses.

Registration of ‘KS Hamilton’ hard red winter wheat

AbstractHard winter wheat (Triticum aestivum L.) is a major crop in semi‐arid western Kansas. The objective of this research was to develop a hard red winter wheat cultivar for western Kansas with high grain yield potential, good baking quality, and resistance to the important diseases in this region, including Wheat streak mosaic virus, Barley yellow dwarf virus, stripe rust, leaf rust, stem rust, and Hessian fly. ‘KS Hamilton’ (Reg. no. CV‐1188, PI 699003) hard red winter wheat was developed by the wheat breeding program at the Agricultural Research Center‐Hays, Kansas State University, and released by the Kansas Agricultural Experiment Station in 2020. KS Hamilton was selected from a three‐way cross of KS08HW176‐4//‘Bill Brown’/KS08HW61‐2. It was released for the dryland production in western Kansas. KS Hamilton was developed using a modified bulk breeding method. KS Hamilton is an F6‐derived line and was tested in yield trials for 6 yr. KS Hamilton has an intermediate maturity and plant height and an average straw strength. It has moderate tolerance to grain shattering and good winterhardiness. KS Hamilton has high grain yield potential in western Kansas and a good disease resistance package, including resistance to Wheat streak mosaic virus, stem rust, and Hessian fly; moderate resistance to Barley yellow dwarf virus; and intermediate resistance to stripe and leaf rusts. KS Hamilton has an average test weight and an above‐average baking quality.

First Report of Sugarcane Mosaic Virus in Zea mays L. in Ukraine

Maize viral diseases especially maize dwarf mosaic disease (MDMD), which is caused by potyviruses, lead to significant crop losses worldwide. Aim. The aim of this work was to identify the causal agent of mosaic symptoms, observed on maize plants during 2018—2020 in Kyiv region. Methods. Enzyme-linked immunosorbent assay in the DAS-ELISA modification using commercial Loewe Biochemica test systems for Maize dwarf mosaic virus (MDMV), Sugarcane mosaic virus (SCMV), Wheat streak mosaic virus (WSMV) were applied to identify the causal agent of maize disease in collected samples. Transmission electron microscopy was used in order to direct viral particle visualisation. Aphids, which are natural vectors of plant viruses, were found on diseased plants. Results. Plants with typical mosaic symptoms were observed in corn crops of the Kyiv region in early June 2018. The pathogen was transmitted by mechanical inoculation to maize and sweet maize plants with the manifestation of mosaic symptoms. Electron microscopy of the sap from diseased plants revealed the presence of flexible filamentous virions 750 nm long and 13 nm in diameter, typical for the genus Potyvirus. In August, mosaic symptoms and aphids Rhopalosiphum padi were found on previously healthy plants in the same maize crop. In 2020, in the same sown area, maize plants were free of viral infection during inspection in June, but a re-inspection in September revealed mosaic symptoms on maize crop and the presence of aphids in the leaf axils. The presence of SCMV in maize samples collected in June and August/September 2018 and 2020, as well as in inoculated maize and sweet maize plants, was confirmed by ELISA using a commercial test system. The obtained data allow suggesting that Rhopalosiphum padi is a natural vector of SCMV in agrocenoses of Ukraine. It should be noted that co-infection with MDMV and WSMV in the affected plants was not detected. Conclusions. This study presents the first report of SCMV in maize in Ukraine.

Virus Diseases of Cereal and Oilseed Crops in Australia: Current Position and Future Challenges.

This review summarizes research on virus diseases of cereals and oilseeds in Australia since the 1950s. All viruses known to infect the diverse range of cereal and oilseed crops grown in the continent’s temperate, Mediterranean, subtropical and tropical cropping regions are included. Viruses that occur commonly and have potential to cause the greatest seed yield and quality losses are described in detail, focusing on their biology, epidemiology and management. These are: barley yellow dwarf virus, cereal yellow dwarf virus and wheat streak mosaic virus in wheat, barley, oats, triticale and rye; Johnsongrass mosaic virus in sorghum, maize, sweet corn and pearl millet; turnip yellows virus and turnip mosaic virus in canola and Indian mustard; tobacco streak virus in sunflower; and cotton bunchy top virus in cotton. The currently less important viruses covered number nine infecting nine cereal crops and 14 infecting eight oilseed crops (none recorded for rice or linseed). Brief background information on the scope of the Australian cereal and oilseed industries, virus epidemiology and management and yield loss quantification is provided. Major future threats to managing virus diseases effectively include damaging viruses and virus vector species spreading from elsewhere, the increasing spectrum of insecticide resistance in insect and mite vectors, resistance-breaking virus strains, changes in epidemiology, virus and vectors impacts arising from climate instability and extreme weather events, and insufficient industry awareness of virus diseases. The pressing need for more resources to focus on addressing these threats is emphasized and recommendations over future research priorities provided.

Impact of Wheat Streak Mosaic Virus on Peroxisome Proliferation, Redox Reactions, and Resistance Responses in Wheat.

Although peroxisomes play an essential role in viral pathogenesis, and viruses are known to change peroxisome morphology, the role of genotype in the peroxisomal response to viruses remains poorly understood. Here, we analyzed the impact of wheat streak mosaic virus (WSMV) on the peroxisome proliferation in the context of pathogen response, redox homeostasis, and yield in two wheat cultivars, Patras and Pamir, in the field trials. We observed greater virus content and yield losses in Pamir than in Patras. Leaf chlorophyll and protein content measured at the beginning of flowering were also more sensitive to WSMV infection in Pamir. Patras responded to the WSMV infection by transcriptional up-regulation of the peroxisome fission genes PEROXIN 11C (PEX11C), DYNAMIN RELATED PROTEIN 5B (DRP5B), and FISSION1A (FIS1A), greater peroxisome abundance, and activation of pathogenesis-related proteins chitinase, and β-1,3-glucanase. Oppositely, in Pamir, WMSV infection suppressed transcription of peroxisome biogenesis genes and activity of chitinase and β-1,3-glucanase, and did not affect peroxisome abundance. Activity of ROS scavenging enzymes was higher in Patras than in Pamir. Thus, the impact of WMSV on peroxisome proliferation is genotype-specific and peroxisome abundance can be used as a proxy for the magnitude of plant immune response.

Full Genome Evolutionary Studies of Wheat Streak Mosaic-Associated Viruses Using High-Throughput Sequencing.

Wheat streak mosaic (WSM), a viral disease affecting cereals and grasses, causes substantial losses in crop yields. Wheat streak mosaic virus (WSMV) is the main causal agent of the complex, but mixed infections with Triticum mosaic virus (TriMV) and High plains wheat mosaic emaravirus (HPWMoV) were reported as well. Although resistant varieties are effective for the disease control, a WSMV resistance-breaking isolate and several potential resistance-breaking isolates have been reported, suggesting that viral populations are genetically diverse. Previous phylogenetic studies of WSMV were conducted by focusing only on the virus coat protein (CP) sequence, while there is no such study for either TriMV or HPWMoV. Here, we studied the genetic variation and evolutionary mechanisms of natural populations of WSM-associated viruses mainly in Kansas fields and fields in some other parts of the Great Plains using high-throughput RNA sequencing. In total, 28 historic and field samples were used for total RNA sequencing to obtain full genome sequences of WSM-associated viruses. Field survey results showed WSMV as the predominant virus followed by mixed infections of WSMV + TriMV. Phylogenetic analyses of the full genome sequences demonstrated that WSMV Kansas isolates are widely distributed in sub-clades. In contrast, phylogenetic analyses for TriMV isolates showed no significant diversity. Recombination was identified as the major evolutionary force of WSMV and TriMV variation in KS fields, and positive selection was detected in some encoding genomic regions in the genome of both viruses. Furthermore, the full genome sequence of a second Kansas HPWMoV isolate was reported. Here, we also identified previously unknown WSMV isolates in the Great Plains sharing clades and high nucleotide sequence similarities with Central Europe isolates. The findings of this study will provide more insights into the genetic structure of WSM-associated viruses and, in turn, help in improving strategies for disease management.