Prevalence, genetic diversity and biological characterization of black mulberry Idaeovirus (BMIV) in Türkiye and Iran

Black mulberry Idaeovirus (BMIV), a recently identified member of Idaeovirus genus, was first detected in Morus nigra L. in Türkiye. Since its initial identification, no comprehensive data have been available regarding its distribution, genetic diversity, or biological behavior across mulberry species. Understanding the epidemiology of BMIV is essential for its management and developing virus-free propagation strategies. Between 2018 and 2021, a total of 479 mulberry samples representing Morus species were collected across 44 provinces in Türkiye, as well as several samples from Iran and Azerbaijan. RT-PCR screening revealed that 87.5% of M. nigra samples (343/392) and 26.3% of M. alba samples (21/80) were infected with BMIV, while other species tested negative. Partial RNA1 sequences (1643 nt) obtained from 167 isolates demonstrated remarkably low genetic variability, with 97.6–99.9% nucleotide identity among Turkish isolates and up to 99.3% identity between Turkish and Iranian isolates. No recombination signals were detected among the isolates. Phylogenetic analyses revealed no clustering based on host species or geographic origin, indicating a highly homogeneous virus population. Graft transmission assays showed that BMIV successfully infected 87.5% of M. australis, followed by 14.3% of M. alba, 70% of M. macroura, and 25% of M. indica. Symptom expression was generally mild, inconsistent, and often associated with mixed infections with mulberry badnavirus 1 (MBV-1), complicating symptom attribution. BMIV is widespread in M. nigra across Türkiye and Iran and displays low genetic diversity. Its ability to infect several Morus species suggests a broader host range than previously known, although symptom expression on leaves remains variable. These findings provide essential insights into BMIV epidemiology and highlight the need to develop virus-free M. nigra propagation systems to support sustainable mulberry production.