Wheat Streak Mosaic Virus Infection Research Articles

Identifying Critical Regulators in the Viral Stress Response of Wheat (Triticum aestivum L.) Using Large-Scale Transcriptomics Data

Wheat (Triticum aestivum L.) cultivation has been globally restricted by many plant viruses such as the Wheat streak mosaic virus (WSMV), Barley stripe mosaic virus (BSMV), and Brome mosaic virus (BMV). Herein, the transcriptome of wheat was in silico analyzed under mono- (WSMV, BSMV, or BMV), bi- (BMV&BSMV, BMV&WSMV, and BSMV&WSMV), and tripartite (WSMV, BSMV, and BMV) infections using the RNA-seq technique. Total numbers of 1616/270, 5243/690 and 5589/2183 differentially expressed genes (DEGs) were up/down-regulated during the bipartite infection of BMV&BSMV, BMV&WSMV and BSMV&WSMV, respectively, while the tripartite infection resulted in the up/down-regulation of 6110/2424 DEGs. The NAC and bHLH were the most commonly presented transcription factor (TF) families in WSMV, BMV, and BSMV infection, while C2H2, bHLH, and NAC were the TF families involved in BMV&WSMV, BMV&BSMV, and BSMV&WSMV infections, respectively. The RLK-Pelle_DLSV was the most commonly expressed protein kinase (PK) family in all infection patterns. Promoter analysis showed that the motifs involved in gene expression, CUL4 RING ubiquitin ligase complex, stress response, brassinosteroid response, and energy-related pathways were significantly induced in wheat plants under bipartite infections. The gene expression network analysis showed that a defense-related gene, i.e., allene oxide synthase (AOS) gene, serves as a crucial hub in tripartite infections.

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.

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.

First Report of High Plains Wheat Mosaic Emaravirus Infecting Foxtail Barley and Wheat in Canada

HomePlant DiseaseVol. 104, No. 12First Report of High Plains Wheat Mosaic Emaravirus Infecting Foxtail Barley and Wheat in Canada PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of High Plains Wheat Mosaic Emaravirus Infecting Foxtail Barley and Wheat in CanadaI. Abdullahi, H. Bennypaul, J. Phelan, R. Aboukhaddour, and M. W. HardingI. AbdullahiCentre for Plant Health, Canadian Food Inspection Agency, North Saanich, BC, V8L 1H3, CanadaSearch for more papers by this author, H. Bennypaul†Corresponding author: H. Bennypaul; E-mail Address: Harvinder.bennypaul@canada.cahttp://orcid.org/0000-0002-3569-7376Centre for Plant Health, Canadian Food Inspection Agency, North Saanich, BC, V8L 1H3, CanadaSearch for more papers by this author, J. PhelanCentre for Plant Health, Canadian Food Inspection Agency, North Saanich, BC, V8L 1H3, CanadaSearch for more papers by this author, R. AboukhaddourAgriculture and Agri-Food Canada, Lethbridge, AB, T1J 4B1, CanadaSearch for more papers by this author, and M. W. Hardinghttp://orcid.org/0000-0002-9322-1894Alberta Agriculture and Forestry, Crop Diversification Centre South, Brooks, AB, T1R 1E6, CanadaSearch for more papers by this author AffiliationsAuthors and Affiliations I. Abdullahi1 H. Bennypaul1 † J. Phelan1 R. Aboukhaddour2 M. W. Harding3 1Centre for Plant Health, Canadian Food Inspection Agency, North Saanich, BC, V8L 1H3, Canada 2Agriculture and Agri-Food Canada, Lethbridge, AB, T1J 4B1, Canada 3Alberta Agriculture and Forestry, Crop Diversification Centre South, Brooks, AB, T1R 1E6, Canada Published Online:20 Oct 2020https://doi.org/10.1094/PDIS-04-20-0872-PDNAboutSectionsView articlePDFSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat View articleHigh Plains wheat mosaic virus (HPWMoV) is a monocistronic octapartite single-stranded negative-sense RNA virus in the genus Emaravirus, family Fimoviridae (ICTV 2018). It infects a number of cereal crops including wheat (Triticum aestivum L.), maize (Zea mays L.), barley (Hordeum vulgare L.), and some weeds (Seifers et al. 1998). HPWMoV is transmitted by the wheat curl mite Aceria tosichella Keifer (Seifers et al. 2009). It can coinfect wheat with some cereal viruses including wheat streak mosaic virus (WSMV) (Burrows et al. 2009). A field survey in southern Alberta, Canada, in late June 2017, evaluated 34 and 37 plants of wheat and grassy weed species, respectively, for the presence of cereal viruses. The sampled wheat plants showed yellow flecks and streaks, with some heavily chlorotic leaves showing necrotic patches along margins. Leaves with extreme symptoms were completely scorched and/or desiccated. Grassy weed species were collected nearby symptomatic wheat but did not show any typical symptoms. The incidence of symptoms varied among the sampled wheat fields, ranging from trace levels to 75% infected. RT-PCR was performed using primers WMoV-F (Byamukama et al. 2016) and WMoV-RR targeting the RNA 3B region of HPWMoV, after total nucleic acid extraction using an in-house procedure (SOP L036-02(a): KingFisher ml total nucleic acid extraction procedure, Sidney Laboratory, Canadian Food Inspection Agency, North Saanich, BC). All primer sequences, their location in the genome, and amplicon sizes are given in the supplementary table. Four wheat plants (one plant of cultivar AAC Elevate and three plants of unknown cultivar) and one foxtail barley plant (Hordeum jubatum L.) from Lethbridge County tested positive for HPWMoV. One wheat plant (cv. Glenn) from the Medicine Hat area also tested positive for HPWMoV. Results were confirmed by two independent RT-PCRs with primers targeting the RNA-6 segment (WmoV-F1 and WmoV-R1) and RNA-2 segment (WmoV-F2 and WmoV-R2), respectively. BLASTn analysis of a representative of each of the two fragments, which have been submitted to NCBI under accession numbers MT124696 and MT124697, showed that they share more than 99% sequence identity with respective RNA sequences of some HPWMoV isolates from the United States (KT988861, KJ939624, KJ939629, and KT988866). All but one of the HPWMoV-infected wheat plants were also positive for WSMV. WSMV infection was confirmed using DAS-ELISA (Agdia, U.S.A.) and RT-PCR with primers targeting the WSMV coat protein (WSMV-CP2 and WSMV-CP4, Dwyer et al. 2007). Next-generation sequencing analysis of one RT-PCR positive sample yielded 10,012,849 clean reads. The dsRNA extraction method, library preparation, sequencing, and bioinformatics analyses were done according to the method of Rott et al. (2017). The obtained clean reads were searched for viral sequences using Virtool software (https://www.virtool.ca), revealing 31 HPWMoV-specific contigs. Sixteen contigs, ranging in length from 252 to 1,728 bp, covered 72.92% of the HPWMoV KS7 isolate genome (KT988860 to KT988868) and shared 95 to 100% identity with it. This virus could be present in, or spread to, other parts of the Canadian prairies where coinfections with other wheat curl mite-transmissible viruses could occur. Coinfections of WSMV and HPWMoV have been reported to correlate with increased symptom severity (Burrows et al. 2009). WSMV infections have led to wheat yield losses of 7 to 18% in the Texas panhandle and in the North American prairies, including Alberta, Canada (Hadi et al. 2011). The appearance of HPWMoV in Canada is concerning because coinfections with WSMV could increase severity and yield loss.The author(s) declare no conflict of interest.

Resistance to Wheat Curl Mite in Arthropod-Resistant Rye-Wheat Translocation Lines

The wheat curl mite, Aceria toschiella (Keifer), and a complex of viruses vectored by A. toschiella substantially reduce wheat yields in every wheat-producing continent in the world. The development of A. toschiella-resistant wheat cultivars is a proven economically and ecologically viable method of controlling this pest. This study assessed A. toschiella resistance in wheat genotypes containing the H13, H21, H25, H26, H18 and Hdic genes for resistance to the Hessian fly, Mayetiola destructor (Say) and in 94M370 wheat, which contains the Dn7 gene for resistance to the Russian wheat aphid, Diuraphis noxia (Kurdjumov). A. toschiella populations produced on plants containing Dn7 and H21 were significantly lower than those on plants of the susceptible control and no different than those on the resistant control. Dn7 resistance to D. noxia and H21 resistance to M. destructor resulted from translocations of chromatin from rye into wheat (H21—2BS/2RL, Dn7—1BL/1RS). These results provide new wheat pest management information, indicating that Dn7 and H21 constitute resources that can be used to reduce yield losses caused by A. toschiella, M. destructor, D. noxia, and wheat streak mosaic virus infection by transferring multi-pest resistance to single sources of germplasm.

Impact of Timing and Method of Virus Inoculation on the Severity of Wheat Streak Mosaic Disease.

Wheat streak mosaic virus (WSMV), transmitted by the wheat curl mite Aceria tosichella, frequently causes significant yield loss in winter wheat throughout the Great Plains of the United States. A field study was conducted in the 2013-14 and 2014-15 growing seasons to compare the impact of timing of WSMV inoculation (early fall, late fall, or early spring) and method of inoculation (mite or mechanical) on susceptibility of winter wheat cultivars Mace (resistant) and Overland (susceptible). Relative chlorophyll content, WSMV incidence, and yield components were determined. The greatest WSMV infection occurred for Overland, with the early fall inoculations resulting in the highest WSMV infection rate (up to 97%) and the greatest yield reductions relative to the control (up to 94%). In contrast, inoculation of Mace resulted in low WSMV incidence (1 to 28.3%). The findings from this study indicate that both method of inoculation and wheat cultivar influenced severity of wheat streak mosaic; however, timing of inoculation also had a dramatic influence on disease. In addition, mite inoculation provided much more consistent infection rates and is considered a more realistic method of inoculation to measure disease impact on wheat cultivars.

Wheat streak mosaic virus: incidence in field crops, potential reservoir within grass species and uptake in winter wheat cultivars

Wheat streak mosaic virus (WSMV) has become a re-emerging pathogen in cereal crops in the Czech Republic. WSMV was first reported in the former Czechoslovakia in the early 1980s, and then no record of the virus was documented until 2009. The incidence of the virus was recorded in recent years in several winter wheat fields and many grass species. Here, we surveyed the incidence of WSMV in cereal crops. The results demonstrated the existence of the virus in winter wheat and volunteer wheat during each year of the monitoring period, which spanned from 2013–2016. Although the range of infected samples was low (6.4% of the total tested samples), a high incidence of well-distributed virus was recorded. In at least six fields, the virus reached severe and potentially epidemic levels. In accordance with our previous report detailing WSMV infection of native grasses, we tested several grass species commonly grown in the Czech Republic. We found that some grass species acted as experimental hosts and possible reservoirs of the virus; these included Anthoxanthum odoratum (sweet vernal grass), Arrhenatherum elatius (false oat-grass), Lolium multiflorum (Italian rye-grass), Bromus japonicus (Japanese chess), Echinochloa crus-galli (barnyard grass), Holcus lanatus (meadow soft grass) and Holcus mollis (creeping soft grass). Some of these grass species are also important weeds of cereals, which may be the potential source of WSMV infection in cereal crops. Several widely used winter wheat cultivars were tested in the field after artificial inoculation with WSMV to evaluate virus titre by RT-qPCR. Overall, the tested cultivars had a low virus titre, which is associated with mild disease symptoms and may provide a good level of crop resistance to WSMV.

Quantifying economic losses associated with levels of wheat streak mosaic incidence and severity in the Texas High Plains

Wheat streak mosaic (WSM), caused by the Wheat streak mosaic virus (WSMV), which is transmitted by the wheat curl mite (Aceria tosichella), is the most prevalent virus disease of wheat in the Texas High Plains. Infected plants initially exhibit mosaic symptoms, which lead to severe stunting, complete chlorosis and, in the most severe cases, eventually plant death. Wheat plants infected with WSMV have lower forage and grain yields and exhibit reduced water-use efficiency compared to non-infected plants. The disease impact on water-use efficiency raises an important issue of whether diseased fields should be irrigated as frequently as non-diseased fields. The issue becomes more relevant when energy costs and the dwindling water resources from the Ogallala Aquifer are taken into consideration. This study examined the potential economic losses due to WSM, using data collected from two fields in 2007 and 2009. A hand-held hyperspectral radiometer was used to quantify severity of WSM in multiple 1 m2 plots along two transects, each stretching from the edges of the fields to their centers. Grain yield declined exponentially (R2 = 0.79, P < 0.0001) with increasing disease severity, as measured by reflectance at 555 nm. For economic analysis, grain yield from each plot was used for determining cost adjustments and linked revenues in relation to WSM severity levels, which allowed calculations of potential profit reduction. The method enables one to compare losses associated with different levels of WSM severity to a baseline with little or no WSMV infection. Results show that losses from the disease are primarily an outcome of reduced revenue due to a decrease in grain yield, and, as expected, losses incurred per unit land area rapidly increase with increasing disease incidence and severity. Furthermore, producers incur additional marginal losses when irrigating fields with WSM because there is little or no return for irrigation inputs, as water-use efficiency of severely diseased wheat is drastically reduced. Results from this study are useful in estimating losses at differing levels of disease incidence and severity and represent the first step in development of an economic threshold for wheat streak mosaic.

Effects of Soil Nitrogen and Atmospheric Carbon Dioxide on Wheat streak mosaic virus and Its Vector (Aceria tosichella Kiefer).

Management of vector-borne plant viruses requires understanding how abiotic (e.g., resource availability) and biotic (e.g., virus-vector interactions) factors affect disease via effects on epidemiological parameters that drive disease spread. We conducted two complementary experiments using Wheat streak mosaic virus (WSMV): (i) a field study to determine the effects of nitrogen (N) fertilization on winter wheat (Triticum aestivum L.) susceptibility to WSMV infection and (ii) a growth chamber study to evaluate the effects of N and carbon dioxide (CO2) enrichment on population growth rates of the wheat curl mite (WCM), the vector of WSMV, and whether the effects of nutrient addition on WCM reproduction were modified by WSMV infection. The relationship between N fertilization and plant susceptibility to WSMV infection was nonlinear, with infection rates increasing rapidly as soil nitrate increased from 0 to 20 ppm and more gradually at higher nitrate concentrations. In the growth chamber study, N fertilization increased WCM population growth rates when the vectors transmitted WSMV but had the opposite effect on nonviruliferous mites. CO2 enrichment had no observable effects on WCM populations. These results suggest that, whereas the spread of WSMV is facilitated by N addition, increases in atmospheric CO2 may not directly alter WCM populations and WSMV spread.

Wheat and Barley Susceptibility and Tolerance to Multiple Isolates of Wheat streak mosaic virus.

One of the greatest virus disease threats to wheat production in the Great Plains of the USA is Wheat streak mosaic virus (WSMV). Breeding programs have developed wheat varieties that are resistant or tolerant to WSMV infection, but these characteristics are climate dependent, and may also vary by WSMV isolate. We tested 10 spring and nine winter wheat (Triticum aestivum) varieties and two barley (Hordeum vulgare) varieties for resistance and tolerance to one WSMV isolate over four years. In spring wheat and barley, there were year by cultivar interactions in terms of resistance and tolerance. However, in winter wheat, yield losses due to WSMV were relatively consistent across years and varieties. Additionally, we tested the impacts of three WSMV isolates individually and in a mixture on twelve, two, and twelve varieties of spring wheat, barley, and winter wheat, respectively. Resistance and tolerance varied by isolate and cultivar, but there were no isolate by cultivar interactions. For spring wheat and barley, yield impacts were greater for two of the three single isolates than for the isolate mixture, whereas in winter wheat, the isolate mixture caused greater yield losses than the individual isolates. Overall, the results indicate that resistance and tolerance phenotypes were influenced by environmental conditions and by WSMV isolate or combination of isolates, suggesting that cultivar screening should be conducted over multiple years and with multiple virus isolates.

Physiological Responses of Hard Red Winter Wheat to Infection by Wheat streak mosaic virus.

Wheat streak mosaic virus (WSMV) causes significant yield loss in hard red winter wheat in the U.S. Southern High Plains. Despite the prevalence of this pathogen, little is known about the physiological response of wheat to WSMV infection. A 2-year study was initiated to (i) investigate the effect of WSMV, inoculated at different development stages, on shoot and root growth, water use, water use efficiency (WUE), and photosynthesis and (ii) understand the relationships between yield and photosynthetic parameters during WSMV infection. Two greenhouse experiments were conducted with two wheat cultivars mechanically inoculated with WSMV at different developmental stages, from three-leaf to booting. WSMV inoculated early, at three- to five-leaf stage, resulted in a significant reduction in shoot biomass, root dry weight, and yield compared with wheat infected at the jointing and booting stages. However, even when inoculated as late as jointing, WSMV still reduced grain yield by at least 53%. Reduced tillers, shoot biomass, root dry weight, water use, and WUE contributed to yield loss under WSMV infection. However, infection by WSMV did not affect rooting depth and the number of seminal roots but reduced the number of nodal roots. Leaf photosynthetic parameters (chlorophyll [SPAD], net photosynthetic rate [Pn], stomatal conductance [Gs], intercellular CO2 concentration [Ci], and transpiration rate [Tr]) were reduced when infected by WSMV, and early infection reduced parameters more than late infection. Photosynthetic parameters had a linear relationship with grain yield and shoot biomass. The reduced Pn under WSMV infection was mainly in response to decreased Gs, Ci, and SPAD. The results of this study indicated that leaf chlorophyll and gas exchange parameters can be used to quantify WSMV effects on biomass and grain yield in wheat.

Epidemiology of Wheat streak mosaic virus in wheat in a Mediterranean-type environment

In a region of Australia with a Mediterranean-type climate Wheat streak mosaic virus (WSMV) infection of wheat occurs in localised epidemics following extended periods when no grass or cereal hosts are present. To achieve a greater understanding of the epidemiology of WSMV in this environment, diverse components of the disease cycle were examined, especially the importance of seed transmission in initiating epidemics. The role of seed transmission in providing WSMV inoculum sources for these epidemics was examined by determining WSMV seed transmission rates and susceptibilities in cereals, and in both annual and perennial grasses that occur locally. Also, examined were the patterns of spread of WSMV from simulated seed-borne infection sources external or internal to wheat plantings. When 11 wheat, 11 oat and seven barley cultivars, and six annual and five perennial grass species, were inoculated with WSMV, all cereal cultivars and annual grass species became infected. In contrast, none of the perennial grass species became infected despite inoculation by both infective sap and wheat curl mite (WCM, Aceria tosichella) vector. When seeds from all WSMV-infected plants from these inoculations to cereals and grasses were germinated, seed transmission was only found in wheat (0.03 to 0.1 %). These findings suggest seed transmission of WSMV is limited to wheat only. In three field studies involving wheat plantings where both simulated WSMV seed-borne infection in wheat and the WCM vector were present, WSMV infection was clustered in plants <4 m from infector plant infection sources. Regardless of whether WSMV infector plants were placed internally or externally, and killed by herbicide or left alive, there were no differences in WSMV spread to wheat plants. In addition, when internal WSMV infection sources were present, the rate and amount of WSMV spread in wheat were directly related to the number of infector plants introduced. Thus, when increasing levels of internal simulated seed-borne infection sources (0.1–1.4 %) were present final WSMV incidence increased (17–97 %). At a natural field infection site, after a long dry summer fallow, volunteer wheat seedlings emerged following autumn rains and were not removed before nine wheat cultivars were sown. All cultivars became infected (78–99 %) and seed transmission rates of 0.03–0.06 % were found in six cultivars. In a Mediterranean-type climate where there is an absence of WSMV infection sources during the hot, dry summer conditions between successive wheat crops, seed-infected wheat seedlings growing as volunteers or from sown infected wheat seed stocks play a critical role in initiating WSMV epidemics.

Joint effects of biotic and abiotic stressors on winter wheat suppression of Bromus tectorum

SummaryIn winter wheat systems in the Northern Great Plains of the United States, Bromus tectorum and wheat streak mosaic virus (WSMV) commonly co‐occur. While independent effects of these pests on wheat yields have been well documented, to our knowledge, no study has investigated whether WSMV modifies interactions between wheat and B. tectorum. Furthermore, the impact that environmental stressors such as nutrient availability have on these interactions has not been addressed. We conducted a randomised split‐plot field study over 2 years to investigate the effects of WSMV and nitrate (N) availability on winter wheat suppression of Bromus tectorum. The study included four N treatments (10–19, 20–31, 31–84, and 85–207 kg ha−1) and two WSMV treatments (mechanically inoculated or control). Increasing soil N increased the susceptibility of wheat to WSMV infection. In 2009, wheat in the lowest and highest N levels had 24% and 65% of plants infected respectively. However, regression analysis indicated that interactive effects of wheat competition, N and WSMV did not play a consistent role in B. tectorum growth. Specifically, the effect of both wheat density and distance from row on B. tectorum biomass remained constant across inoculation treatments, suggesting that wheat inoculated with WSMV suppressed B. tectorum as effectively as healthy wheat. Furthermore, wheat had a greater impact on B. tectorum growth in higher N environments, even though incidence of WSMV infection in wheat was highest. Overall, our results suggest that WSMV infection may not change the ability of wheat to suppress B. tectorum.

Consensus Mapping and Identification of Markers for Marker‐Assisted Selection of Wsm2 in Wheat

ABSTRACTA recently identified Wheat streak mosaic virus (WSMV) resistance gene Wsm2 confers a high level of resistance. Objective of this study was to identify closely linked DNA markers for Wsm2 for use in marker‐assisted selection (MAS) in wheat (Triticum aestivum L.). Two segregating populations (CO960293‐2 × ‘TAM 111’ and CO960293‐2 × ‘Yuma’) of F2:3 families were evaluated for response to WSMV infection in growth chamber experiments. Forty‐eight simple sequence repeat (SSR) or sequence‐tagged site (STS) markers were screened for polymorphism between the parents of both populations. In the CO960293‐2 × TAM 111 population, five markers were mapped to the region of Wsm2 with XSTS3B‐55 being the closest marker (5.2 cM distal to Wsm2). In the CO960293‐2 × Yuma population, eight markers were linked to Wsm2 with the closest marker Xbarc102 linked at 3.9 cM proximal to Wsm2. Results from consensus mapping of the two populations suggested that Xbarc102 was distal to Wsm2. The marker Xbarc102 was associated with Wsm2 in all 22 wheat lines derived from crosses between susceptible parents and either CO960293‐2 or ‘RonL’ (also carrying Wsm2). The marker allele Xbarc102‐219‐bp present in CO960293‐2 was amplified in polymerase chain reaction (PCR) from Wsm2‐carrying genotypes CO960293‐w133, RonL, and ‘Snowmass’ but not from the resistant line KS96HW10‐3 (carrying Wsm1) or the susceptible genotypes ‘Karl 92’, ‘TAM 107’, and ‘N96L9970’. Therefore, this marker should be useful for MAS of Wsm2 in breeding programs.

Wheat Curl Mite Resistance: Interactions of Mite Feeding With Wheat Streak Mosaic Virus Infection

The majority of plant viruses are dependent on arthropod vectors for spread between plants. Wheat streak mosaic virus (family Potyviridae, genus Tritimovirus, WSMV) is transmitted by the wheat curl mite, Aceria tosichella Keifer, and this virus and vector cause extensive yield losses in most major wheat (Triticum aestivum L.)-growing regions of the world. Many cultivars in use are susceptible to this vector-virus complex, and yield losses of 10-99% have been documented. wheat curl mite resistance genes have been identified in goat grass, Aegilops tauschii (Coss) Schmal., and transferred to hexaploid wheat, but very few varieties contain effectively wheat curl mite resistance, due to virulent wheat curl mite populations. However, wheat curl mite resistance remains an effective strategy to reduce losses due to WSMV. The goal of our project was to identify the most effective, reproducible, and rapid method for assessing wheat curl mite resistance. We also wanted to determine whether mite resistance is affected by WSMV infection, because the pathogen and pest commonly occur together. Single and group wheat curl mite infestations produced similar amounts of leaf rolling and folding on wheat curl mite-susceptible wheat varieties that were independent of initial wheat curl mite infestation. This finding will allow accurate, efficient, large-scale screening of wheat germplasm for wheat curl mite resistance by infesting plants with sections of wheat leaf tissue containing mixed stages of wheat curl mite. The wheat curl mite-resistant breeding line 'OK05312' displayed antibiosis (reduced wheat curl mite population development). The effect of WSMV infection on wheat curl mite reproduction was genotype-dependent. Mite populations increased on infected wheat curl mite- and WSMV-susceptible plants compared with uninfected plants, but WSMV infection had no significant effect on wheat curl mite populations on resistant plants. OK05312 is a strong source of wheat curl mite resistance for wheat breeding programs.

Occurrence and Yield Effects of Wheat Infected with Triticum mosaic virus in Kansas.

Triticum mosaic virus (TriMV) infects wheat (Triticum aestivum) in the Great Plains region of the United States. This study determined the occurrence of TriMV at three locations over 3 years and yield effects of wheat mechanically infected with TriMV. Wheat infection with TriMV, Wheat streak mosaic virus (WSMV), and the High Plains virus (HPV) was verified using enzyme-linked immunosorbent assay. Both wheat singly infected with TriMV and doubly infected with TriMV and WSMV occurred at three, two, and one locations in 2007, 2008, and 2009, respectively. Wheat singly infected with HPV occurred at one and two locations in 2008 and 2009, respectively. Wheat doubly infected with WSMV and HPV occurred at one location in 2008 and 2009. Infection with TriMV declined at two locations each year and, at the third location, it increased the second year and was not detected the third year. WSMV infection increased, except for a decline the third year at one location. In contrast to 3.0% infection of wheat with TriMV and WSMV at one location, 85% of the wheat 1.6 km from that site was infected with TriMV and WSMV in 2009. Infection of wheat with TriMV caused significant yield and volume weight reductions in Danby, RonL, and Jagalene but not KS96HW10-3 wheat.

A Dominant Gene for Resistance to Wheat Streak Mosaic Virus in Winter Wheat Line CO960293‐2

Wheat streak mosaic (WSM), caused by Wheat streak mosaic virus (WSMV), is a devastating disease in wheat (Triticum aestivum L.) in the Great Plains of North America. Use of resistance is an effective and environmentally sound method to control the disease. In this study, six wheat genotypes were compared for their responses to WSMV infection under growth chamber conditions. The three resistant genotypes, KS96HW10‐3 (Wsm1), Mace (Wsm1), and CO960293‐2, had disease scores significantly lower than the remaining three genotypes without major resistance. Disease in TAM 111 and TAM 112 was consistently less severe than Karl 92. A population consisting of 188 F2:3 families derived from the cross CO960293‐2 × TAM 111 was used for determining inheritance of the WSMV resistance and for molecular mapping of the resistance in CO960293‐2. Data on segregation of resistance indicated that the resistance in CO960293‐2 is conditioned by a single dominant gene, which was named Wsm2 Transgressive segregation toward susceptibility occurred in the population suggesting a minor gene in the moderately susceptible parent TAM 111, which was not allelic to Wsm2. Wsm2 was mapped to the short arm of chromosome 3B with two flanking simple sequence repeat markers. The single dominant gene inheritance for WSMV resistance in CO960293‐2 has been consistent with the observations that the resistance can be readily transferred to adapted cultivars.

Hairpin RNA derived from viral NIa gene confers immunity to wheat streak mosaic virus infection in transgenic wheat plants

Wheat streak mosaic virus (WSMV), vectored by Wheat curl mite, has been of great economic importance in the Great Plains of the United States and Canada. Recently, the virus has been identified in Australia, where it has spread quickly to all major wheat growing areas. The difficulties in finding adequate natural resistance in wheat prompted us to develop transgenic resistance based on RNA interference (RNAi). An RNAi construct was designed to target the nuclear inclusion protein 'a' (NIa) gene of WSMV. Wheat was stably cotransformed with two plasmids: pStargate-NIa expressing hairpin RNA (hpRNA) including WSMV sequence and pCMneoSTLS2 with the nptII selectable marker. When T(1) progeny were assayed against WSMV, ten of sixteen families showed complete resistance in transgenic segregants. The resistance was classified as immunity by four criteria: no disease symptoms were produced; ELISA readings were as in uninoculated plants; viral sequences could not be detected by RT-PCR from leaf extracts; and leaf extracts failed to give infections in susceptible plants when used in test-inoculation experiments. Southern blot hybridization analysis indicated hpRNA transgene integrated into the wheat genome. Moreover, accumulation of small RNAs derived from the hpRNA transgene sequence positively correlated with immunity. We also showed that the selectable marker gene nptII segregated independently of the hpRNA transgene in some transgenics, and therefore demonstrated that it is possible using these techniques, to produce marker-free WSMV immune transgenic plants. This is the first report of immunity in wheat to WSMV using a spliceable intron hpRNA strategy.

Life history of the bird cherry‐oat aphid, Rhopalosiphum padi, on transgenic and non‐transformed wheat challenged with Wheat streak mosaic virus

AbstractThe life history of the bird cherry‐oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), was studied via laboratory assays on Wheat streak mosaic virus (WSMV)‐infected and non‐infected transgenic and non‐transformed wheat [Triticum aestivum L. (Poaceae)]. Although R. padi is not a WSMV vector, it is known to colonize WSMV‐infected wheat plants. Two transgenic soft white winter wheat genotypes, 366‐D03 and 366‐D8, that express the WSMV coat protein gene, and the WSMV‐susceptible non‐transformed cultivar Daws were tested. All genotypes showed disease symptoms when infected with WSMV. Whereas plant height was significantly reduced on virus‐infected compared to non‐infected plants of all genotypes, virus‐infected transgenic plants exhibited lower virus titer and lower disease rating scores than Daws. No significant effects of WSMV infection or genotypes were observed on the length of R. padi nymphal development period, nor on their pre‐, and post‐reproductive periods. Rhopalosiphum padi reproductive period was significantly longer on Daws infected with WSMV than on non‐infected plants of this cultivar. In contrast, there were no significant differences in length of R. padi reproductive period between virus‐infected and non‐infected transgenic plants within a genotype. Rhopalosiphum padi daily fecundity was significantly lower and adult longevity significantly longer on virus‐infected than on non‐infected plants of all genotypes. Total aphid fecundity and intrinsic rate of increase were not significantly different among treatments. The percentage of winged aphids that developed was greater on WSMV‐infected compared to non‐infected plants within a genotype. Results indicate that both virus infection status of plants and wheat genotype influence the life history of R. padi.

An evolutionary approach identifies and exploits effective FHB resistance in hitherto susceptible wheat germplasm

It has proved difficult to combine high FHB resistance with desirable agronomic and quality traits while advancing through cycles of crosses with elite but FHB-susceptible parents. Instead of aiming to transfer the complement of genes that condition FHB resistance in such sources as Sumai 3, our goal is to emulate in the desired germplasm the evolution of resistance that occurred in Sumai 3 as it derived from moderately susceptible parents. Genes in resistance pathways induced by Fusarium inoculation that are present in FHB-resistant wheat lines are also present and expressed in counterpart FHB-susceptible near-isogenic lines. Wheat cultivars and otherwise adapted germplasm may thus already contain the necessary genes but remain susceptible because expression is not coordinated effectively. The required heritable alteration of expression can be induced by growing repeated generations of virus-susceptible wheat plants under pressure from systemic infection with wheat streak mosaic virus (WSMV), as we have shown for such traits as height, maturity and virus resistance. As the components of FHB resistance (PR genes induced by Fusarium) are already present, variations induced by repeated cycles of WSMV infection combined with selection under FHB pressure evolve FHB resistance, apparently de novo, from hitherto susceptible germplasm. We present examples of Canadian bread and durum wheat germplasm that show FHB resistance generated by this approach.