| Verticillium wilt (VW) of potato caused by V. dahliae (V.d.) is one of the most difficult problems for potato health management worldwide. Breeding potato for VW resistance has not been so successful. In this study the quantitative polymerase chain reaction (PCR) assay was used to assess V.d. colonization level (represented by V.d. DNA level) in a potato breeding population (149 clones). After three greenhouse tests, 16 clones were found consistently resistant to V.d. Four among the 16 clones were identified as tolerant clones (light VW symptoms with high pathogen level). A linear relationship between VW score and pathogen colonization was found for 65 clones in one of the two formal greenhouse tests, and for 105 advanced potato breeding selections in a field trial. Among 81 control plants with VW-like symptoms, most (77 clones) contained no V.d. signal, which indicated assessment of resistance based solely on symptom expression may not be reliable. |
