The table below shows the concentration of phytoalexins (antimicrobial chemicals produced by plants) in the leaf tissues of three different cultivars of potato plants (Solanum tuberosum) 24 hours after inoculation with the pathogen Phytophthora infestans.
| Cultivar | Phytoalexin concentration (arbitrary units) |
|---|---|
| Cultivar X | 14 |
| Cultivar Y | 19 |
| Cultivar Z | 165 |
Explain why the data in the table suggests that Cultivar Z has mounted an active chemical defence response against the pathogen.
