First Report of Blueberry Latent Virus in Blueberry in Germany

Blueberries, especially the cultivated varieties that originate from the North American species Vaccinium corymbosum, are enjoying growing popularity worldwide as a healthy fruit. Blueberries are a high-value crop, and the area under cultivation in Germany has doubled over the last 15 years. Several dozen viruses infect blueberries, predominantly in North America (Martin et al. 2012; Saad et al. 2021); however, little is known about the spread of these viruses in Europe. As the importance of the crop has grown, the first problems, some of which may have been virus-related, have become apparent, and a targeted effort has been launched to survey the virome of cultivated blueberries in Germany. Blueberry mosaic virus was the first identified due to its conspicuous mosaic symptoms (Menzel et al. 2021). In subsequent studies, two viruses first identified in the United States, blueberry virus L and blueberry mitovirus, have been confirmed in Europe (Menzel et al. 2024). Between 2023 and 2025, 15 samples were collected at random from asymptomatic plants from 9 fields of V. corymbosum in Lower Saxony, the main blueberry growing region in Germany. Total RNA was extracted from bark tissue using a Spectrum Plant Total RNA Kit (Sigma-Aldrich, USA). Following library preparation, the samples were sequenced on an Illumina NextSeq2000 high-throughput sequencing (HTS) platform. Assembled sequences were analysed with an in-house developed pipeline using Geneious Prime software, which allowed the reconstruction of the complete coding sequence of an amalgavirus in three samples, showing the highest nucleotide sequence identities to blueberry latent virus (BBLV, species Amalgavirus vaccinii). Two of the isolates, Liberty-23 (blueberry cv. Liberty, GenBank Accession No. PX505943) and Seedling-6 (unknown cv., PX505944) are identical to each other and possess a single nucleotide polymorphism compared to the reference sequence of BBLV (NC_014593). The sequence of the third isolate, Duke-23 (cv. Duke, PX505942), had three nucleotide polymorphisms compared to the respective reference sequence. These values confirm the extremely high conservation of the BBLV genome. To confirm the presence of BBLV, the extracted RNA was subjected to RT-PCR using the primer pair BBLV-Fwd: 5′-CCTGCAACGGATTCGCTAGAA-3′ and BBLV-Rev: 5′-AGGGCAAAACTTCGTGGAGA-3′, which target a 647 bp fragment. Amplicons of the expected size were obtained for all three samples, and direct Sanger sequencing confirmed the identity of the virus. This is the first evidence of the occurrence of BBLV in Germany, a virus that is expected to be difficult to eliminate even in breeding programmes due to its high seed-transmission rate. The exclusively vertical transmission of amalgaviruses indicates that they spread through their association with cultivars. Besides North America and Asia, the virus has only been detected to date in Eastern Europe, that is Serbia, and Bosnia and Herzegovina (Delić et al. 2022). Although the involvement of amalgaviruses in disease symptoms is controversial and the investigated blueberries showed no obvious symptoms, this report provides further evidence of the need for certification criteria for blueberry cultivation material in general. Since blueberry plantations involve high establishment costs and typically remain productive for 20 years or more, it is impossible to quickly clear any infected stock. To date, there is no mandatory testing in Europe, which leaves the door open to further introduction and spread of viral diseases in cultivated blueberries. This could be avoided by applying strict certification schemes, ideally utilising HTS. This work received funding from the innovation programme of the Federal Ministry of Agriculture, Food and Regional Identity (Germany) under grant No. FKZ 281D124C21 by decision of the German Bundestag. The authors are grateful to Lara Lintl and Viola Weichelt for their excellent technical assistance.