Phytophthora infestans is able to penetrate epidermal
cells of many different plant species, including non-host
plants, which indicated that, the defense responses mainly
occur post-penetration (Vleeshouwers et al., 2000). In the
early phases of interaction, there are only small differences
between compatible and incompatible reactions (Cuypers &
Hahlbrock, 1988; Freytag et al., 1994). Differences in the
plant’s reaction are discernible once the hyphae reach the
mesophyll. In compatible interaction, some cells undergo
hypersensitive response (HR), but the hypha can escape and
continue to colonize the tissue. In the incompatible
interaction, a larger number of cells undergo HR and the
pathogen is contained and dies