Identification of a Divergent Isolate of Ryegrass Mosaic Virus in Ohio Wheat.

A divergent isolate of ryegrass mosaic virus (RGMV) has been identified that is associated with wheat samples collected in Ohio. The complete genome of the virus is 9,570 nucleotides, with a polyprotein open reading frame that shares 77.2% nucleotide sequence identity with the reference ryegrass mosaic virus sequence.

Occurrence and High-Throughput Sequencing of Viruses in Ohio Wheat.

Ohio is a leading producer of soft red winter wheat in the United States. Many viruses impact wheat production, but there is a lack of contemporary information on the distribution and potential impact of wheat viruses in Ohio. To address this knowledge gap, we created a comprehensive dataset of viruses identified by high-throughput sequencing (HTS) and their incidence in field sites sampled across the state. Samples were collected from 103 field sites in surveys conducted in 2012, 2016, and 2017 and subjected to RNA HTS, reverse transcription (RT) PCR, or enzyme-linked immunosorbent assay to assess virus sequence diversity, prevalence, and incidence within fields. Partial and complete virus sequences were assembled and detection validated by RT-PCR. Assembled sequences were compared with previously known virus sequences, and novel sequences were validated by Sanger sequencing. The viruses detected most often included barley yellow dwarf virus (BYDV), cereal yellow dwarf virus (CYDV), wheat streak mosaic virus (WSMV), and wheat spindle streak mosaic virus (WSSMV). These viruses were detected at 67, 69, 55, and 28% of the field sites sampled, with mean incidences of 18, 19, 20, and 49%, respectively, within fields where they were detected. Brome mosaic virus (BMV) and cocksfoot mottle virus (CfMV) were also viruses of potential importance detected in Ohio, found in 26 and 17% of the field sites sampled, respectively. Based on results from logistic regression analyses, the presence of BYDV, CYDV, WSMV, and WSSMV was associated with the presence of volunteer wheat, BYDV and CfMV with monocots as the previous crop, and BMV with the presence of nearby corn fields (P < 0.10). For six viruses, there was evidence of spatial clustering in at least one field site and the variance of mean incidence was higher at the county level than at the regional spatial level. This finding suggests that county- and site-specific factors influenced the incidence and spatial pattern of some viruses. The results of this study provide a snapshot of viruses present in Ohio wheat and insights into their biology, potential risks to wheat production, and possible management strategies.

Characterization of an Ohio Isolate of Brome Mosaic Virus and Its Impact on the Development and Yield of Soft Red Winter Wheat.

Brome mosaic virus (BMV) is generally thought to be of little economic importance to crops; consequently, there is little information about its impact on wheat production under field conditions. After repeated detection of BMV in Ohio wheat fields at incidences up to 25%, the virus was isolated, sequenced, characterized, and tested for its impact on soft red winter wheat (SRWW). The Ohio isolate of brome mosaic virus (BMV-OH) was found to be >99% identical to a BMV-Fescue isolate (accession no. DQ530423-25) and capable of systemically infecting multiple monocot and dicot species, including cowpea and soybean, in experimental inoculations. BMV-OH was used in field experiments during the 2016 and 2017 growing seasons to quantify its effect on SRWW grain yield and development when inoculated at Feekes 1, 5, 8, and 10 in two to four cultivars. Cultivar and timing of inoculation had statistically significant (P < 0.05) main and interaction effects on grain yield, wheat growth, and multiple components of yield. Compared with noninoculated controls, BMV-OH reduced grain yield by up to 61% when inoculated at Feekes 1 and by as much as 25, 36, and 31% for inoculations at Feekes 5, 8, and 10, respectively. The magnitude of the yield reduction varied among cultivars and was associated with reductions in grain size and weight or plant population. These findings suggest that BMV could impact wheat productivity in Ohio and will serve as the basis for more large-scale investigations of the effects of this virus in commercial fields.