Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2015
Publication Date: 11/15/2015
Publication URL: https://handle.nal.usda.gov/10113/5695371
Citation: Stewart, L.R. 2015. Sequence diversity of wheat mosaic virus isolates. Virus Research. 213:299-303.
Interpretive Summary: High Plains disease is important in production of both wheat and maize in the United States. The disease emerged in the United States High Plains states in 1993 and its known distribution has expanded in subsequent years. Wheat mosaic virus (WMoV), transmitted by eriophyid wheat curl mites (Aceria tosichella) is the causal agent of disease. WMoV and related viruses (classified in the genus Emaravirus) are difficult to study because of the complexities of their unusual genomes and mite transmission. Thus, only recently was the complete genome sequence for WMoV reported. Different WMoV isolates have been shown to have different partial sequences and different transmission rates by wheat curl mite populations, which is important for assessing disease potential in the field. However, sequence information needed to compare isolates and understand their biological differences has never been available. Therefore, we sequenced all 8 genome segments of three additional WMoV isolates collected from wheat, barley, or maize in Ohio and Kansas to compare to the sequenced Nebraska isolate and partial sequences of five other isolates. Our results show two significantly different groups (>16% nucleotide sequence divergence) of WMoV isolates. Neither group was associated with a particular host or collection location (state). The two groups differed not only in sequence identity but in number of genome segments. While the Nebraska isolate-like virus isolates each contained two different copies of the virus segment encoding the nucleocapsid protein (3A and 3B), the second group contained only one nucleocapsid segment copy distinct from 3A and 3B. Together, these comparisons provide a basis to understand the biological differences between WMoV isolates that could be important for disease development and spread.
Technical Abstract: High Plains disease of wheat and maize emerged in the United States in 1993 and its distribution has expanded in subsequent years. Wheat mosaic virus (WMoV), transmitted by eriophyid wheat curl mites (Aceria tosichella) is the causal agent of disease. WMoV and other members of the genus Emaravirus evaded thorough molecular characterization for many years because of their multisegmented negative sense RNA genomes and mite transmission, which created challenges in fulfilling Koch’s postulates and identifying all of the virus genome segments. More emaraviruses have been characterized in recent years, each with four to six genomic segments reported. Recently, 8 segments of Wheat mosaic virus, plus a variant sequence of the nucleocapsid protein-encoding segment was reported for a Nebraska isolate. Consensus sequences of the more WMoV isolates are compared to the Nebraska isolate here: an Ohio maize isolate (GG1), a Kansas barley isolate (KS7), and an Ohio wheat isolate (W1). Partial sequences of two other Ohio wheat isolates (H1 and K1) and other available partial sequences, are also compared. Results show two distinct groups of WMoV isolates. Ohio wheat isolate RNA segments showed 84% or lower nucleotide sequence identity to the NE isolate, whereas GG1 and KS7 had 98% or higher nucleotide sequence identity to the NE isolate. Interestingly, both of the nucleoprotein-encoding genome segment 3 variant sequences (3A and 3B) reported for the NE isolate were found in the similar isolates herein, but a single distinct RNA3 was observed for each of the Ohio wheat isolates. From our results, it appears that there are at least two distinct sequence groups of WMoV in the continental United States.