The development of Septoria tritici blotch on seedling leaves of the wheat cultivars Shafir (susceptible) and KVZ-K4500 L.6.A.4 (resistant) was studied by light and fluorescence microscopy. Appressoria were usually located above a stomatal opening. Percentage germination, formation of appressoria and the pattern of invasion of the substomatal chamber were the same in the susceptible and resistant cultivars. Growth of hyphae was observed in the intercellular spaces of the leaf tissue of both cultivars.
Autofluorescence was more commonly observed in the resistant accession, as was the affinity for trypan blue dye. Some lignification of cell walls and sparse deposition of callosic materials occurred in the resistant line. Leaves of KVZ-K4500 L.6.A.4, which macroscopically appeared pycnidia-free, revealed microscopically the presence of arrested, immature, pycnidia-like aggregations that did not progress further under prolonged environmental conditions conducive for pycnidial induction.