Host–parasite interfaces in a resistant and a susceptible cultivar of Solanum tuberosum inoculated with Phytophthora infestans: leaf tissue

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Abstract
Host–parasite interfaces in leaves from a resistant (Eba) and a susceptible (Bintje) potato cultivar inoculated with Phytophthora infestans were studied using light and electron microscopy. Host penetration occurs similarly in both cultivars either through stomata or directly through the epidermis. In the susceptible host the fungus spreads throughout the tissue intercellularly and transcellularly, whereas in the resistant host it remains confined to the focus of infection. Yet in both cases live, normal-appearing hyphae can be observed even after 5 days. The appearance of haustoria in both cultivars is similar: they are either surrounded by an extrahaustorial matrix alone or in combination with wall appositions (collars or encasements). Structures with cytological features between those of haustoria and transcellular hyphae were also recorded, indicating a variety of host–parasite interactions within leaf tissue. Sporulation has been observed on the susceptible cultivar but not on the resistant one. The results suggest that cellular reactions against the intruding fungal hypha are qualitatively similar in both cultivars but that at the tissue level the intercellular spread of the pathogen and its sporulation are prevented in the resistant host but not in the susceptible host.