Differential Expression of Potato Defence Genes Associated with the Salicylic Acid Defence Signalling Pathway in Response to Weakly and Highly Aggressive Isolates of Verticillium dahliae

Verticillium wilt is a vascular disease affecting hundreds of important dicotyledonous crops worldwide. Its main causal agent in potato is Verticillium dahliae Kleb. A differential potato-V.dahliae system consisting of two cultivars of potato (susceptible; S and moderately resistant; MR) and two V.dahliae isolates (weakly, WA and highly aggressive, HA), was used to evaluate the expression of five defence-related genes, PAL1, PAL2, PR-1, PR-2 and PR-5. These genes were selected because they are in general associated with the salicylic acid defence signalling pathway. Expression levels of these genes were assessed in potato roots and leaves at 0, 4 and 21h (hpi), and 3, 7 and 14days postinoculation (dpi). In the roots, the expression of PAL1, PR-1 and PR-2 in the MR was higher than in the susceptible cultivar in response to inoculation with either one of the tested V.dahliae isolates. PAL2 gene expression increased gradually starting at 21hpi in the MR cultivar as opposed to the susceptible one. Higher expression of PR-1 was detected at 7dpi in roots. In the leaves, both PAL1 and PAL2 genes showed higher expression in the MR cultivar relative to the susceptible one. Interestingly, the expression of PR-2 was slightly higher in the susceptible cultivar. Combined data analyses revealed that PAL1, PAL2, PR-1 and PR-2 genes are regulated at the transcriptional level in response to infection by V.dahliae. These results indicate that the salicylic acid pathway is also involved in potato defence against V.dahliae and add to the data gathered to elucidate the signalling mechanisms in this hostpathogen interaction.