Biology subjects

Ohlson, E. W.

Publications and source records attributed to Ohlson, E. W..

3 recordsLinked to original sources

bioRxiv2026

Deep sequencing of High Plains wheat mosaic virus from sweet corn to guide seed health testing reveals multiple variants for all eight genome segments and two major isolate types

High Plains wheat mosaic virus (HPWMoV) is a wheat and maize-infecting virus of phytosanitary concern due to its potential for seed transmission. Recent phytosanitary restrictions have required sweet corn seed lots to test negative for HPWMoV prior to import into certain countries. To inform the design of more sensitive and broad-spectrum diagnostic primers for seed health testing and phytosanitary certification, we performed deep sequencing of HPWMoV-positive tissue collected from fields in two major sweet corn seed production regions in the Pacific Northwest, the Columbia Basin and Treasure Valley. Virus-like particle enrichment prior to Illumina sequencing facilitated near complete genome coverage (>95%) for the 21 HPWMoV isolates sequenced. De novo assembly of the eight viral genome segments revealed high levels of diversity for each segment, with at least two variants identified for each RNA and three variants for RNA3, RNA6, and RNA8. Within each sample, only one variant per RNA segment was usually present, with the notable exception of RNA3, sorting each isolate into what we designated type A and type B isolates. All but one previously sequenced HPWMoV isolate can be sorted into these two types. Two samples contained at least two variants for every RNA, totaling 17 genome segments, potentially representing a co-infection of type A and type B isolates. Despite this variability, we successfully designed two primer and probe sets for reverse transcription-quantitative polymerase chain reactions (RT-qPCR) that detected all 20 isolates tested in a duplex diagnostic assay, making the assay suitable for seed health testing for HPWMoV.

plant biology↗

bioRxiv2026

The genetic architecture of maize yellow mosaic virus resistance in corn

Maize yellow mosaic virus (MaYMV) is an emerging polerovirus of corn and other grass species. Due to its broad host range and transmission by multiple aphid species, management strategies such as crop rotations, pesticides, and weed control are likely ineffective. Therefore, resistant cultivars are needed. In this study, we characterized the Goodman 282 maize diversity panel for its response to MaYMV. Leaf reddening symptoms were quantified, and diagnostics were performed to assess infection and obtain a semi-quantitative measure of virus titer. Low titer lines and inbreds representing symptomatic and asymptomatic infected phenotypic classes were characterized further by RT-qPCR. Genome-wide association studies were performed using MLM, FarmCPU, and BLINK models to identify SNPs associated with disease. In total, 64% of lines were asymptomatically infected. Although all lines tested positive for infection by MaYMV in at least one experiment, Ky226 had reduced viral titer compared to other lines. Sixteen quantitative trait nucleotides (QTN) were identified, many of which are linked to genes implicated in flavonoid, carotenoid, and phenolic metabolic pathways as well as antiviral defense. Notably, a QTN associated with a chalcone synthase, a key enzyme in the flavonoid biosynthesis pathway, was detected by even the most conservative, MLM model. These results indicate that the genetic architecture of corn in response to MaYMV is complex, and that developing immune cultivars may not be achievable using natural sources of genetic variation. However, this study provides a foundation for breeding maize with improved tolerance and advances our understanding of host response to MaYMV infection.

genetics↗

bioRxiv2024

Characterization of three resistance-breaking isolates of sugarcane mosaic virus from Rwanda and implications for maize lethal necrosis

Maize lethal necrosis (MLN) is a devastating disease of maize caused by synergy between two viruses: maize chlorotic mottle virus (MCMV) and a potyvirus, most often sugarcane mosaic virus (SCMV). Throughout the 2010s, severe MLN outbreaks occurred in sub-Saharan East Africa including Kenya, Rwanda, and Ethiopia. In this study, we assessed the virulence of SCMV isolates collected from Rwanda by screening a panel of maize near isogenic lines containing different combinations of major potyvirus resistance loci. We discovered that the three Rwandan SCMV isolates tested could overcome all three potyvirus resistance loci even when used in combination, including one isolate that could asymptomatically infect all resistant lines tested. To understand how SCMV virulence may contribute to MLN, each of the three isolates were co-inoculated with MCMV on a panel of SCMV and MCMV resistant maize lines. No significant differences in MLN severity were observed for the Rwandan isolates compared to the reference SCMV isolates, indicating that increased virulence in SCMV single infection does not necessarily correlate with increased MLN severity in co-infection with MCMV. For all SCMV isolates tested, at least two potyvirus resistance loci were needed to reduce MLN severity, and maize lines with a combination of SCMV and MCMV resistance were most effective. Surprisingly, in some cases co-infection with MCMV facilitated SCMV infection of potyvirus resistant lines that SCMV could not infect alone. These results underscore the challenges of developing durable MLN resistance and highlight the importance of incorporating strong, multigenic potyvirus resistance into MLN resistance breeding programs.

plant biology↗