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.

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 three-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 DAS-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 MSU 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 ‘WB9879CL’ in 2019, demonstrating a high degree of susceptibility to WSMV inoculation. Barley cultivars had considerably lower WSMV incidence compared to 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.

Management of the Wheat Curl Mite and Wheat Streak Mosaic Virus With Insecticides on Spring and Winter Wheat

The wheat curl mite (WCM, Aceria tosichella, Keifer) is an eriophyid mite species complex that causes damage to cereal crops in the Northern Great Plains by feeding damage and through the transmission of plant viruses, such as wheat streak mosaic virus. Insecticide treatments were evaluated in the greenhouse and field for efficacy at managing the WCM complex on wheat. Treatments tested were carbamates, organophosphates, pyrethroids, a neonicotinoid seed treatment, mite growth inhibitors, and Organic Materials Review Institute–approved biocontrols, soaps, and oils. Treatment with carbamates, organophosphates, and pyrethroids decreased WCM in greenhouse trials compared with untreated controls 14 days after infestation. The seed treatment, mite growth inhibitors, and organic pesticides did not reduce WCM populations effectively and consistently. The timing of application was tested using a sulfur solution as the experimental treatment. Treating plants with sulfur seven days after mite infestation reduced mites compared with the untreated control. In contrast, prophylactically applied sulfur and sulfur applied 14 days after mite infestation were not effective. When tested under field conditions with plots infested with viruliferous mites, there was no yield difference detected between untreated control plots and plots sprayed with insecticides. Select carbamates, organophosphates, and pyrethroids have a potential for use in greenhouse mite management when appropriate.

Biological and molecular characterisation of the two Polish Wheat streak mosaic virus isolates and their transmission by wheat curl mites

Wheat streak mosaic virus (WSMV) is a serious and widespread pathogen in the wheat-producing areas in the USA while, in Europe, it has been considered a minor threat to cereal crops. In the past, WSMV was detected in wheat, triticale and maize plants in Poland by DAS-ELISA. Here, we present the biological and molecular characterisation of WSMV-Sze and WSMV-Sosn isolates collected from western and southern Poland and report their transmissibility by the widespread wheat curl mite (WCM) lineage MT-8. The performed bioassays revealed that the analysed WSMV isolates infect wheat, barley, triticale, rye, oat and maize, but they differ in the symptoms induced on the infected plants. Moreover, they infect Bromus hordeaceus Linnaeus, which is increasingly recognised as a virus reservoir. The full-length genome sequence of both isolates was obtained and compared with the others described to date. The phylogenetic analysis revealed that the Polish isolates are clustered with the earlier described type B isolates of WSMV from Europe and Iran. The recombination analysis revealed the presence of recombinant variants in WSMV population and indicated that the WSMV-Sosn might originated from the intra-species recombination of the WSMV-Sze and WSMV-Cz isolates.

Wheat dwarf virus and its impact on the 2020 harvest in some regions of Ukraine

Goal. Identify the virus that causes symptoms of dwarfism and non-earing of winter wheat (reduced or no ear formation), and investigate its effect on plant yields. Methods. Visual diagnostics, enzyme-linked immunosorbent assay in double sandwich modification (DAS-ELISA), polymerase chain reaction, biometric, determination of yield and its structure, statistical data processing. Results. A study of winter wheat varieties from Vinnytsia, Khmelnytsky, Kyiv, Chernihiv and Cherkasy regions with symptoms of dwarfism, yellowing of leaves and non-earing. ELISA and PCR have shown that the disease is caused by Wheat dwarf virus. The absence of Wheat streak mosaic virus, Barley yellow dwarf virus, Brome mosaic virus and Wheat spindle mosaic virus (Wheat streak mosaic virus) was shown in the studied samples. It was found that the dwarf wheat virus significantly reduces the number of grains in the ear (3.3 times), the weight of grains from the ear (3.4 times) and the weight of 1000 grains (1.9—3.3 times) depending on the degree of damage plants (from moderate to severely affected). Conclusions. The circulation of dwarf wheat virus in agrocenoses of five regions of Ukraine and a significant negative impact of the disease on the yield of winter wheat plants have been established. The obtained results indicate the need for constant monitoring and testing of plants for the presence of wheat dwarf virus in Ukraine.

Occurrence and molecular characterization of wheat streak mosaic virus in wheat in Serbia

The wheat streak mosaic virus (WSMV), vectored by the wheat curl mite, is globally distributed and threatens wheat production worldwide. Since its first occurrence in Serbia in the 1960s, WSMV presence has not been monitored. In 2019, a total of 62 samples of fi ve wheat cultivars from eight locations in Serbia were collected and tested for the presence of nine common wheat viruses: WSMV, barley yellow dwarf virus-PAV, -MAV, -SGV, and -RMV, cereal yellow dwarf virus-RPV, wheat spindle streak virus, brome mosaic virus, and soil-borne wheat mosaic virus, using individual or multiplex RT-PCR. WSMV was detected in 58.1% of the tested samples in seven wheat crops at five different locations. Species-specific primers failed to detect the presence of the other eight tested viruses. For further confirmation of WSMV, RT-PCR with the WS8166F/WS8909R primers covering the coat protein (CP) gene was carried out for both amplification and sequencing. The amplified product of the correct predicted size (750 bp) derived from four selected isolates, 98-19, 99-19, 102-19 and 120-19, was sequenced and deposited in GenBank (MT461299, MT461300, MT461301 and MT461302, respectively). Serbian WSMV isolates showed very high nucleotide identity (98.16-99.02%) and shared a deletion of triplet codon GCA at nucleotide position 8412- 8414 resulting in deletion of glycine amino acid (Gly2761). Phylogenetic analysis conducted on CP gene sequences revealed the existence of four clades, named A, B, C and D, and one recently introduced clade B1. All Serbian wheat WSMV isolates grouped into clade B together with other European isolates and one isolate from Iran. The results of this study provide the first insight into molecular characterisation of Serbian WSMV isolates, indicating their close relationship with other European isolates and existence of a single genotype in the country. Phylogenetic analysis also confirms the dispersal of WSMV isolates throughout Europe from a single locus.

Transgenic Wheat Harboring an RNAi Element Confers Dual Resistance Against Synergistically Interacting Wheat Streak Mosaic Virus and Triticum Mosaic Virus

Wheat streak mosaic virus (WSMV) and triticum mosaic virus (TriMV) are economically important viruses of wheat (Triticum aestivum L.), causing significant yield losses in the Great Plains region of the United States. These two viruses are transmitted by wheat curl mites, which often leads to mixed infections with synergistic interaction in grower fields that exacerbates yield losses. Development of dual-resistant wheat lines would provide effective control of these two viruses. In this study, a genetic resistance strategy employing an RNA interference (RNAi) approach was implemented by assembling a hairpin element composed of a 202-bp (404-bp in total) stem sequence of the NIb (replicase) gene from each of WSMV and TriMV in tandem and of an intron sequence in the loop. The derived RNAi element was cloned into a binary vector and was used to transform spring wheat genotype CB037. Phenotyping of T1 lineages across eight independent transgenic events for resistance revealed that i) two of the transgenic events provided resistance to WSMV and TriMV, ii) four events provided resistance to either WSMV or TriMV, and iii) no resistance was found in two other events. T2 populations derived from the two events classified as dual-resistant were subsequently monitored for stability of the resistance phenotype through the T4 generation. The resistance phenotype in these events was temperature-dependent, with a complete dual resistance at temperatures ≥25°C and an increasingly susceptible response at temperatures below 25°C. Northern blot hybridization of total RNA from transgenic wheat revealed that virus-specific small RNAs (vsRNAs) accumulated progressively with an increase in temperature, with no detectable levels of vsRNA accumulation at 20°C. Thus, the resistance phenotype of wheat harboring an RNAi element was correlated with accumulation of vsRNAs, and the generation of vsRNAs can be used as a molecular marker for the prediction of resistant phenotypes of transgenic plants at a specific temperature.