The potato leaf tissues infected with Phytophthora infestans(Mont.) DeBary, and treated with the culture filtrate of P. infestans(Race 1) were investigated by means of electron-microscope(HS-6). The leaf tissues were fixed-with 6.25% glutaraldehyde for 4 hours and fixed again with 4% osmium tetraoxide solution for 3 hours.
The cell wall of the mycelia of P. infestans was composed of inner and outer layers. Mitochondria, nuclei, ER and vacuoles were observed in the hyphae. Fungal hyphae were obseved in the intercellular space and in the suscept cells(cultivar Irish Cobbler, Katahdin and Norin No.1) infected by P. infestans. Mucilaginous substance was observed on the suscept cell wall contacted by the fungal hyphae.
In the cells of potato tissues infected by the fungus, substance in low electron density was observed in the nuclear matrix, and the disappearance of nuclear membrane was recoginzed. Disintegration of chloroplast membrane and the swelling of the grana structure was observed in the infected cells. Osmiophilic granules were also recognized in the chloroplast, but starch grains were not observed. Decreased number of cristae was recognized in the mitochondria and microbody membrane disappeared, Sometimes plasmolysis was observed in the suscept cells.
Browning occured in the potato tuber slices - Norin No. 1 and interspecific hybrid 1506-b(9) - treated with the culture filtrate. Wilt and necrosis was observed by the treatment of the culture filtrate on potato leaves (Norin No. 1 and interspecific hybrid 1506-b(9)).
Although curved grana structure was observed in the chloroplast. Tonoplast was destroyed in the potato cells treated with the culture filtrate . Accumulation of high electron-dense substance was recognized around the cell wall of interspecific hybrid 1506-b(9) treated with the culture filtrate of P. infestans, but this phenomenon was not observed in the case of treating cultivar Norin No. 1 with the culture filtrate. Plasmolysis was not observed in the cells of both cultivars treated with the culture filtrate.