First Report of Broad Bean Wilt Virus 1 Infecting Purple‐Coneflower in Germany

Echinacea purpurea (family Asteraceae; purple coneflower) is cultivated worldwide as an ornamental herbaceous perennial and for its medicinal use. In summer 2022, conspicuous virus symptoms were observed on plants of three different commercial varieties in an outdoor research trial which had been planted in spring 2002 at the Julius Kühn Institute, Braunschweig, Germany (Figure 1). Numerous plants showed mosaic symptoms (Figure 2), some, particularly the white-flowering cv. White Swan, also showed noticeable leaf deformations (Figure 3). The other two varieties were purple-flowering and came from different sources, but are of an unknown variety. To date, the occurrence of broad bean wilt virus 2, cucumber mosaic virus (CMV), tobacco rattle virus, tomato ring spot virus and tomato spotted wilt virus have been reported in coneflower (Li et al. 2012). To identify and propagate possible viruses involved, a diseased leaf sample of E. purpurea cv. White Swan was mechanically inoculated onto Nicotiana tabacum cv. Samsun nn, which developed a leaf mosaic systemically (16 days post-inoculation). Subsequently, total RNA was extracted using a RNeasy Plant Mini Kit (Qiagen, Germany) and the derived library sequenced on an Illumina NextSeq2000 high-throughput sequencing platform. Analysis of the assembled sequences (Geneious Prime, New Zealand) allowed the identification of the complete genome sequence of a fabavirus (GenBank Accession Nos. PX423618 [RNA 1] and PX423619 [RNA 2]) showing the highest nucleotide identity to broad bean wilt virus 1 (BBWV1) (RNA 1 [PQ162448], 99.7%; RNA 2 [MZ202346], 91.0%) and of a cucumovirus (OQ993369–OQ993371) with highest sequence identity to CMV (RNA 1 [OR607778], 99.3%; RNA 2 [HE793684], 99.3%; RNA 3 [PP256256], 98.2%). No other viruses were detected in the inoculated host. To confirm the presence of these two viruses in the crop, six individual diseased plants of each cultivar were sampled and tested serologically for CMV (DSMZ, Germany; ELISA RT-0929) and BBWV1 (DSMZ, Germany; ELISA RT-0548) using standard DAS-ELISA. All plants showed a strong positive reaction for both viruses. CMV, which is considered one of the viruses with the largest host range, is known to be able to infect coneflower. BBWV1, originally identified in broad beans, is known to occur in numerous host plants outside the plant family Fabaceae but its occurrence in plants of the genus Echinacea has not been reported. As all coneflower plants were infected with both viruses, and possibly others, it is unclear to what extent the symptoms observed can be attributed to each virus individually. Both viruses are known to be efficiently transmitted by various aphid species, which makes control more difficult. Nevertheless, all plant material traded should be certified virus-free, given the severity of the symptoms caused. The authors thank L. Lintl, V. Bicknäse and U. Zender for technical assistance and E. Jeworutzki for growing and maintaining the plants.