The expression of general resistance to late blight (Phytophthora infestans) in potato leaves

Summary

Resistance toPhytophthora infestans was evaluated histologically using leaves of potato cultivars with different levels of general resistance. Host genotype did not influence the preinfectional processes of encysted zoospores, e.g. frequency of germination, length of germ tubes, or frequency of formation of appressoria. Most of the appressoria on the leaf surface were attached to epidermal cells, but they were also found on cells of the stomatal complexes, on hairs and glands, and on cells adjacent to vascular tissue. There were significant differences between cultivars in the extension of intercellular hyphal growth and branching 24 and 48 h after inoculation, the differences increasing with time. In contrast to cv. Bintje, the hyphae in the most resistant cultivar Matilda were mostly confined to the epidermal and palisade cells even 48 h after infection, the number of hyphae per section was much lower, and sporulation capacity was reduced.