Acquisition and transmission of potato mop‐to furovirus by a culture of Spongospora subterranea f.sp. subterranea derived from a single cystosorus

Potato mop‐top virus (PMTV) was detected by ELISA in primary zoospores from four out of six isolates of Spongospora subterranea f.sp. subterranea. One virus‐free isolate (N) of S. subterranea was used to acquire PMTV from potato roots and to transmit the virus to healthy plants. A mono‐fungal culture of S. subterranea (isolate N) was derived by infecting tomato plant roots with a single cystosorus. The culture was used successfully to acquire PMTV from the roots of infected Nicotiana debneyi plants that had been manually inoculated with virus isolates, and subsequently to transmit the virus to healthy bait plants. These experiments confirm that S. subterranea is a vector of PMTV. Two PMTV isolates that had been maintained by manual inoculation for 19 and 21 passages were also acquired and transmitted by the fungus culture.