THE HISTOLOGY OF PROCESSES ASSOCIATED WITH THE INFECTION OF RESISTANTAND SUSCEPTIBLE WHEAT CULTIVARS WITH SEPTORIA-TRITICI

The development of Septoria tritici blotch on seedling leaves of the w heat cultivars Shafir (susceptible) and KVZ-K4500 L.6.A.4 (resistant) was studied by light and fluorescence microscopy. Appressoria were usu ally located above a stomatal opening. Percentage germination, formati on of appressoria and the pattern of invasion of the substomatal chamb er 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 re sistant accession, as was the affinity for trypan blue dye. Some ligni fication of cell walls and sparse deposition of callosic materials occ urred in the resistant line. Leaves of KVZ-K4500 L.6.A.4, which macros copically appeared pycnidia-free, revealed microscopically the presenc e of arrested, immature, pycnidia-like aggregations that did not progr ess further under prolonged environmental conditions conducive for pyc nidial induction.