Metagenomic Sequencing of Maize Reveals Abundant Genomic RNA of a Comovirus, a Genus Previously Known to Infect Only Dicots.

To better understand the diversity of viral pathogens in Türkiye, a major exporter of cereals in Europe, we performed high-throughput sequencing of total RNA from maize plants collected in the Trakya region. Certain maize plants exhibiting mosaic and mottle symptoms, gathered from Tekirdağ province in Trakya, yielded large numbers of reads corresponding to the genome of a divergent strain of a comovirus, which corresponds to turnip ringspot virus (TuRSV), a recognized species of the genus Comovirus. This finding is unexpected because all known comoviruses infect only dicotyledonous species, and the known host range of TuRSV has been limited to plants in the Brassicaceae family. The nearly complete and partial nucleotide sequences of the bipartite genome of the maize isolate, as named TuRSVTR59, consist of 6,027 nt TuRSV-TR59 RNA1 and 3,920 nt TuRSV-TR59 RNA2, excluding poly (A) tails. RNA1 and RNA2 each encode a single ORF of 1,860 and 1,096 codons, respectively. Phylogenetic analysis demonstrated that TuRSV-TR59 from Türkiye clustered with other TuRSV isolates from diverse hosts and regions, showing highest identity to isolates from Germany, Czech Republic, and Croatia (80.56-77.77% and 92.09-90.50% nucleotide and amino acid sequence identities, respectively). The ability of TuRSV-TR59 isolate to infect maize was confirmed by reverse transcription polymerase chain reaction. Surveys in the Tekirdağ province of Türkiye, done in 2022-2025, revealed that 2 out of 145 maize samples (1.38%) and 8 out of 116 canola samples (6.89%) were found infected with TuRSV. This is the first report of a comovirus in maize from a monocotyledonous plant species.