FIG. 7.

Transmission electron micrographs of cross sections of cucumber roots inoculated with either P. ultimum alone (A) or F. oxysporum strain Fo47 (B through E). (A) Pythium hyphae (P) develop abundantly in all root tissues, causing some host cell wall (HCW) alterations. (B through E) Attempts of Fo47 hyphae to penetrate the epidermis are often halted by the formation of hemispheric wall appositions (WA) at sites of potential penetration (B and C). Elongated and stratified wall appositions are also seen in areas proximal to attempted fungal penetration (D, arrows). Electron-dense deposits (E, arrows) surround an Fo47 cell (F), which is distorted. Bars: A through C, 2 μm; D, 0.5 μm; E, 1 μm.