Fine structure of the early interaction of lily roots with Fusarium oxysporum f.sp lilii

The early interaction of lily roots with the cortical rot pathogen Fusarium oxysporum f.sp. lilii was studied using roots of lily bulblets grown in Hoagland's solution, inoculated with the pathogen, and sampled up to 48 h later. Conidia produced germ tubes within 6 h, which extended towards and into the mucilage covering the root elongation zone, and along and into the anticlinal grooves and middle lamellae of epidermal cells. By 24-48 h, infecting hyphae had reached the periclinal walls and intercellular spaces between the epidermis and the outermost cells of the cortex. Penetration of intercellularly growing hyphae directly across host cell walls was not observed; invasion of the cell lumen only occurred by gradual infringing of hyphae upon successive primary wall layers. Non-cellulosic wall appositions rich in vesicles and covered by a cellulosic protective-like layer were formed in response to approaching hyphae in resistant cv.Connecticut King, but rarely in susceptible cv. Esther which seemed more susceptible to plasmolysis and rot. Finger-like projections of the appositions into the host cell cytoplasm likely represent early stages of transfer cell formation.