Factors affecting the detection of potato mop-top virus in potato tubers and improvement of test procedures for more reliable assays

Progeny tubers were harvested from plants of five potato cultivars that had been grown in potato mop-top virus (PMTV) infested soil. The tubers were tested for virus infection by methods based on reverse transcriptase-polymerase chain reaction (RT-PCR) or enzyme-linked immunosorbent assay (ELISA) incorporating monoclonal antibodies. Both RT-PCR and ELISA detected PMTV in extracts from tuber flesh. However, when the assay results were compared for individual tubers, there was an incomplete correlation between the two methods, and more infected tubers were detected by ELISA than by RT-PCR. PMTV was detected in some samples but not in others taken from different parts of the same tuber, and this uneven distribution may explain the discrepancy between the results of the ELISA and RT-PCR tests. Storage of tubers of two cvs at an elevated temperature (20°C) for 4 wk prior to testing, nearly doubled the number of sample sites at which PMTV was detected by ELISA. Such pre-treatment may improve the accuracy of tuber tests. Most tubers of cvs Saturna and Pentland Crown were symptomlessly infected indicating that PMTV may easily escape detection in tubers of these cvs if tests are based solely on presence of visual symptoms. The application of post-harvest tuber testing, particularly to cvs that do not display obvious symptoms, and the subsequent elimination of contaminated tubers will help to provide effective control of spread, and the establishment of PMTV at new sites.