Replication and Movement of In Vitro-Generated Infectious RNAs of Potato Mop-Top Virus RNAs in Mechanically Inoculated Two Potato Cultivars

Potato mop-top virus (PMTV), vectored by soil-borne protist Spongospora subterranea f. sp. subterranea (Sss) is increasingly becoming a threat to potato production in the USA. Major means of spread is through infected tubers, vector, and contaminated farm equipment, and the virus is known to be mechanically poorly transmitted. Using infectious cDNA clones of PMTV, in vitro produced viral RNA transcripts were used to mechanically inoculate two potato cultivars differing in their sensitivity to PMTV, as well as model plants Nicotiana benthamiana, and N. tabacum. Infection was measured using primers to each of the three genomic RNAs by real-time PCR. The movement of all three genomic RNAs and their relative accumulation were studied over several time points. Overall, 100% of the inoculated plants showed infection. All three RNAs of PMTV were detected in younger, uninoculated leaves at 7, 14, and 21 dpi, suggesting successful infection followed by long distance movement. Potato cv. Clearwater Russet had higher levels of PMTV compared to Castle Russet, which was in agreement with their response to PMTV under natural field conditions. Findings suggest that the use of infectious RNA transcripts in combination with mechanical inoculation has the potential to study PMTV-potato interactions at the omics level.