Natural transmission of blueberry mosaic-associated virus (Ophiovirus vaccinii) in cultivated and wild blueberries by Olpidium virulentus and its potential role in disease epidemiology

Blueberry ( Vaccinium spp.) is the second most significant berry crop globally, and its economic importance in Türkiye has increased markedly in recent years. Blueberry mosaic-associated virus (BlMaV) has been identified as the causal agent of a significant disease known as blueberry mosaic disease (BMD) reported from several countries, including Türkiye. Recently, concerns have been raised regarding the natural spread of virus due to the presence of BlMaV both in cultivated and wild blueberries. In this study, we investigated the potential involvement of Olpidium spp. in the natural transmission of BlMaV in blueberry plantations. Several trap plants, such as lettuce, carrot, broccoli, and cucumber, were co-cultivated with virus-free in vitro propagated blueberry plants (cv. ‵Bluecrop‵) in soils collected from root zones of BlMaV-infected blueberries grown in a commercial orchard and two wild plantations in Rize province located in the Black Sea Region of Türkiye. When the samples taken from the capillary roots of all trap plants and in vitro blueberry plants were stained and examined under a light microscope, resting spores of the Olpidium species were observed on some of the lettuce, broccoli, carrot, and the adjacent in vitro blueberry roots one month after planting. All plants used in the experimental transmission trials were subjected to PCR/RT-PCR to verify the presence of both Olpidium spp. and BlMaV. The presence of Olpidium virulentus on the roots of trap plants and blueberry was confirmed by PCR analysis using both generic (ITS1/ITS4) and species specific primer pairs. While a high BlMaV infection rate was detected in the leaves of lettuce and adjacent blueberries planted in soil collected from the root zones of BlMaV-infected blueberries from all three locations, the virus could not be detected in other trap plants. However, only in location 3, two blueberry plants planted next to broccoli and one blueberry plant planted next to carrots were found to be infected by BlMaV. This study confirms the transmission of BlMaV by O. virulentus under natural conditions. Additionally, our findings indicate that BlMaV is effectively transmitted in wild blueberry plantations, which may elucidate the transmission of BlMaV from wild blueberries to cultivated plantations or vice versa.