First report of turnip yellow virus infecting rapeseed (<i>Brassica napus</i>) in Uruguay

Turnip yellows virus (TuYV), a member of the genus Polerovirus (family Solemoviridae), is one of the most important pathogens of Brassica napus (rapeseed) worldwide. The virus has a broad host range including crop (Stevens et al., 2008) and weed species (Slavíková et al., 2022). In winter 2023, symptoms characteristic of TuYV infection, dwarfing and reddened to purple leaves, were observed on crops of rapeseed cv. Phoenix in western Uruguay (Fig. 1). Symptoms were most conspicuous in August. Three farms showing TuYV infection symptoms were studied: La Armonía (-32.0337139, -57.89684), Bichadero (-32.640178, -57.461587), and Horqueta (-32.977245, -57.703312). Approximately 80% of the plants on these farms showed signs of infection (Fig. 2). The presence of the aphid vector of TuYV, Myzus persicae, was confirmed on all three farms, suggesting a potential pathway for virus transmission. In total, seven diseased plants were sampled from La Armonía, five from Bichadero, and three from Horqueta. Total RNA was extracted from pooled diseased leaves of each plant. Reverse transcription was performed with random hexamers, followed by treatment with DNase I. Two sets of primers were used for PCR amplification based on Slavíková et al. (2022). The primer pair TuYV3terF1/TuYV3terR1 amplifies a 696 bp fragment related to the coat protein of TuYV, while TuYV_5cpF/TuYVR-K2 amplifies a 797 bp fragment related to the movement protein and the P3a protein of TuYV. All samples from La Armonía, Bichadero and Horqueta tested positive for TuYV with both primer sets. Amplified products of the expected size obtained from six plant samples, representing all localities, were Sanger sequenced (Macrogen, Korea). BLASTn analysis of the TuYV3terF1/TuYV3terR1 and TuYV_5cpF/TuYVR-K2 fragment sequences (GenBank Accession Nos. PV125736-PV125745) revealed nucleotide identities of 93.7 to 99.4% (query coverage 100%) with previously reported TuYV sequences (MT586571.1, MT586577.1, LR584027.1, OK030793.1, and OK030750.1), confirming the infection of rapeseed with TuYV. To complement the molecular data with serological tests, leaf samples from the 15 plants tested by RT-PCR and an extra negative sample (cv. Phoenix) grown in the greenhouse were analysed using a turnip yellows virus DAS-ELISA kit (Loewe Biochemica, Germany). The DAS-ELISA results confirmed the RT-PCR detection of TuYV in all samples. This report marks the first identification of TuYV in Uruguay. The presence of similar symptoms on some farms in the past two years suggests that the virus may have been circulating for at least three years. The cultivar Phoenix is an early sown winter crop and the autumn of 2023 in Uruguay was unusually warm, which may have boosted M. persicae growth, exposing the crop to the aphid vector of TuYV. These findings underscore the need for ongoing monitoring of TuYV in Uruguay. This work was supported by PEDECIBA Uruguay and Unicampo Uruguay SRL.