Further evidence of mulberry vein banding-associated orthotospovirus as the causal agent of yellow ringspot disease in mulberry ( Morus spp.)

Mulberry vein banding-associated orthotospovirus (MVBV) is an orthotospovirus reported to infect mulberry (Morus spp.) plants. However, its pathogenicity to mulberry has not yet been determined. Recently, MVBV was detected by high-throughput sequencing (HTS) in mulberry plants exhibiting mulberry yellow ringspot (MYRS) disease in Zhenjiang, Jiangsu, China. Mechanical transmission assays using crude sap failed to infect its natural host, mulberry, and an experimental host, Nicotiana benthamiana, indicating that MVBV is not readily mechanically transmissible. To determine its pathogenicity, ring budding, a grafting propagation method, was employed to transmit MVBV to disease-free mulberry plants. Successful infection was confirmed by RT-PCR and RT-qPCR, indicating that MVBV is graft transmissible. The infected plants developed characteristic MYRS symptoms, including yellow spots and ringspots. HTS analysis of the progeny viruses confirmed that MVBV was the only detectable pathogen in these infected plants. Collectively, these results confirmed for the first time that MVBV induces MYRS disease in mulberry plants.