Eriophyid mite-transmitted, multipartite, negative-sense RNA plant viruses with membrane-bound spherical virions are classified in the genus Emaravirus. We report here that the eriophyid mite-transmitted Wheat mosaic virus (WMoV), an Emaravirus, contains eight genomic RNA segments, the most in a known negative-sense RNA plant virus. Remarkably, two RNA 3 consensus sequences, encoding the nucleocapsid protein, were found with 12.5% sequence divergence, while no heterogeneity was observed in the consensus sequences of additional genomic RNA segments. The RNA-dependent RNA polymerase, glycoprotein precursor, nucleocapsid, and P4 proteins of WMoV exhibited limited sequence homology with the orthologous proteins of other emaraviruses, while proteins encoded by additional genomic RNA segments displayed no significant homology with proteins reported in GenBank, suggesting that the genus Emaravirus evolved further with a divergent octapartite genome. Phylogenetic analyses revealed that WMoV formed an evolutionary link between members of the Emaravirus genus and the family Bunyaviridae. Furthermore, genomic-length virus-and virus-complementary (vc)-sense strands of all WMoV genomic RNAs accumulated asymmetrically in infected wheat, with 10-to 20-fold more virus-sense genomic RNAs than vc-sense RNAs. These data further confirm the octapartite negative-sense polarity of the WMoV genome. In WMoV-infected wheat, subgenomic-length mRNAs of vc sense were detected for genomic RNAs 3, 4, 7, and 8 but not for other RNA species, suggesting that the open reading frames present in the complementary sense of genomic RNAs are expressed through subgenomic-or near-genomic-length vc-sense mRNAs. IMPORTANCEWheat mosaic virus (WMoV), an Emaravirus, is the causal agent of High Plains disease of wheat and maize. In this study, we demonstrated that the genome of WMoV comprises eight negative-sense RNA segments with an unusual sequence polymorphism in an RNA encoding the nucleocapsid protein but not in the additional genomic RNA segments. WMoV proteins displayed weak or no homology with reported emaraviruses, suggesting that the genus Emaravirus further evolved with a divergent octapartite genome. The current study also examined the profile of WMoV RNA accumulation in wheat and provided evidence for the synthesis of subgenomic-length mRNAs of virus complementary sense. This is the first report to demonstrate that emaraviruses produce subgenomic-length mRNAs that are most likely utilized for genome expression. Importantly, this study facilitates the examination of gene functions and virus diversity and the development of effective diagnostic methods and management strategies for an economically important but poorly understood virus. E riophyid mite-transmitted, multipartite single-stranded RNA plant viruses with negative polarity recently were classified in the genus Emaravirus (1). The Emaravirus virions are membranebound particles of 80 to 200 nm in diameter, resembling those of Tospovirus. Members of the genus Emaravirus possess four...

A series of Wheat streak mosaic virus (WSMV)-based expression vectors were developed by engineering a cycle 3 GFP (GFP) cistron between P1 and HC-Pro cistrons with several catalytic/cleavage peptides at the C-terminus of GFP. WSMV-GFP vectors with the Foot-and-mouth disease virus 1D/2A or 2A catalytic peptides cleaved GFP from HC-Pro but expressed GFP inefficiently. WSMV-GFP vectors with homologous NIa-Pro heptapeptide cleavage sites did not release GFP from HC-Pro, but efficiently expressed GFP as dense fluorescent aggregates. However, insertion of one or two spacer amino acids on either side of NIb/CP heptapeptide cleavage site or deletion in HC-Pro cistron improved processing by NIa-Pro. WSMV-GFP vectors were remarkably stable in wheat for seven serial passages and for 120 days postinoculation. Mite transmission efficiencies of WSMV-GFP vectors correlated with the amount of free GFP produced. WSMV-GFP vectors infected the same range of cereal hosts as wild-type virus, and GFP fluorescence was detected in most wheat tissues.

The soybean gall midge (Resseliella maxima Gagné) was recently identified as a new species causing injury to soybean in the Midwestern United States. Although this insect was only recently identified, it has likely been present in soybean fields for at least the last 8 yr based on anecdotal reports. The soybean gall midge has historically been observed late in the season on soybean plants that were believed to have been previously compromised by a plant pathogen or mechanical damage with little to no concern for economic losses. In late June 2018, dead and dying plants were found to be associated with the soybean gall midge across four midwestern states. The distribution of plant injury in the field, larval feeding within the stem, and timing of infestation indicate that it is likely an important pest of soybean. Yield losses in soybean gall midge infested fields can be up to 100% for the first 30 meters from the field edge, with losses of 17–31% further into the field. The rapid development of the soybean gall midge as an important pest of soybean has left large gaps in the knowledge necessary to develop an integrated pest management program.

Wheat streak mosaic virus (WSMV), type member of the genus Tritimovirus in the family Potyviridae, is an economically important virus causing annual average yield losses of approximately 2 to 3% in winter wheat across the Great Plains. The wheat curl mite (WCM), Aceria tosichella, transmits WSMV along with two other viruses found throughout the Great Plains of the United States. Two common genotypes of WSMV (Sidney 81 and Type) in the United States share 97.6% nucleotide sequence identity but their transmission relationships with the WCM are unknown. The objective of this study was to determine transmission of these two isolates of WSMV by five WCM populations (‘Nebraska’, ‘Montana’, ‘South Dakota’, ‘Type 1’, and ‘Type 2’). Nonviruliferous mites from each population were reared on wheat source plants mechanically inoculated with either Sidney 81 or Type WSMV isolates. For each source plant, individual mites were transferred to 10 separate test plants and virus transmission was determined by a double-antibody sandwich enzyme-linked immunosorbent assay. Source plants were replicated nine times for each treatment (90 individual mite transfers). Results indicate that three mite populations transmitted Sidney 81 at higher rates compared with Type. Two mite populations (Nebraska and Type 2) transmitted Sidney 81 and Type at higher rates compared with the other three populations. Results from this study demonstrate that interactions between virus isolates and mite populations influence the epidemiology of WSMV.

McMechan, A. J., Tatineni, S., French, R., and Hein, G. L. 2014. Differential transmission of Triticum mosaic virus by wheat curl mite populations collected in the Great Plains. Plant Dis. 98:806-810. Wheat is an important food grain worldwide and the primary dryland crop in the western Great Plains. A complex of three wheat curl mite (WCM)-transmitted viruses (Wheat streak mosaic virus. High plains virus, and Triticum mosaic virus [TriMV]) is a cause of serious loss in winter wheat production in the Great Plains. TriMV was ftrst reported in Kansas in 2006 and later found in most other Great Plains states.Currently, three populations of WCM have been identified by genetic characterization and differential responses to mite resistance genes in wheat. In this study, we examined TriMV transmission by these three WCM populations: 'Nebraska' (NE), 'Montana' (MT), and 'South Dakota' (SD). Mite transmission using single-mite transfers revealed that the NE WCM population transmitted TriMV at 41%, while the MT and SD WCM populations failed to transmit TriMV. In multi-mite transfers, the NE WCM population transmitted TriMV at 100% level compared with 2.5% transmission by MT and SD WCM populations. Interestingly, NE mites transferred during the quiescent stages following the first and second instar transmitted TriMV at a 39 to 40% rate, suggesting that immature mites were able to acquire the virus and maintain it through molting. In addition, mite survival for single-mite transfers was significantly lower for NE mites when transferred from TriMV-inoculated source plants (60%) compared with mockinoculated source plants (84%). This demonstrates potentially negative effects on WCM survival from TriMV. TriMV transmission differences demonstrated in this study underscore the importance of identification of mite genotypes for future studies with TriMV.

Triticum mosaic virus (TriMV) (genus Poacevirus, family Potyviridae) is a recently described eriophyid mite-transmitted wheat virus. In vitro RNA transcripts generated from full-length cDNA clones of TriMV proved infectious on wheat. Wheat seedlings inoculated with in vitro transcripts elicited mosaic and mottling symptoms similar to the wild-type virus, and the progeny virus was efficiently transmitted by wheat curl mites, indicating that the cloned virus retained pathogenicity, movement, and wheat curl mite transmission characteristics. A series of TriMV-based expression vectors was constructed by engineering a green fluorescent protein (GFP) or red fluorescent protein (RFP) open reading frame with homologous NIa-Pro cleavage peptides between the P1 and HC-Pro cistrons. We found that GFP-tagged TriMV with seven or nine amino acid cleavage peptides efficiently processed GFP from HC-Pro. TriMV-GFP vectors were stable in wheat for more than 120 days and for six serial passages at 14-day intervals by mechanical inoculation and were transmitted by wheat curl mites similarly to the wild-type virus. Fluorescent protein-tagged TriMV was observed in wheat leaves, stems, and crowns. The availability of fluorescent protein-tagged TriMV will facilitate the examination of virus movement and distribution in cereal hosts and the mechanisms of cross protection and synergistic interactions between TriMV and Wheat streak mosaic virus.

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Intensive study for more than 100 yr has resulted in a good understanding of corn's (Zea mays L.) growth and development. However, abnormal development of ears in corn was reported in several U.S. states, including Texas, Colorado, Kansas, Nebraska, Iowa, and Illinois, during 2016, stretching our understanding. A comprehensive review of the literature was conducted to identify abnormal ears' symptoms, causes, and timing of development. This study aimed to (a) describe and summarize previously reported ear symptoms, (b) document recent widespread symptoms of major concern, and (c) describe our current understanding of the potential cause(s) and expected development timing for abnormal ears. In total, 10 previously reported symptoms of corn ears were found, including tassel, fasciated, arrested, pinched, blunt, silk-balled, incomplete kernel set, banana-shaped, zipper, and tipped-back. Three additional recent widespread symptoms of major concern associated with significant yield reduction across a wide area in 2016 were described: multi-ears, barbell-ears, and short-husk ears. The information available on several of the symptoms was limited, and the specific causes were unknown, highlighting the need for more research in this area. Despite this and based on existing knowledge, possible causal factors and postulated development timing (i.e., when the stress may have occurred) are presented for all symptoms. Abnormal ear development can be seen as the response to complex interactions among genetics, environment, and management practices. Ear abnormalities are detrimental to grain yield and quality, and their mitigation is imperative to efficient corn systems, crop resiliency, and sustainability.