An electron microscope study of infection and disease development in cucumber hypocotyls inoculated with Cladosporium cucumerinum

Abstract Infection and disease development in hypocotyls of cucumber ( Cucumis sativus L.) seedlings inoculated with conidia of the scab fungus Cladosporium cucumerinum Ell. and Arth. have been studied using the electron microscope. The conidia seem to adhere to the surface by a secreted material. The germ tube dissolves the cuticle, then the hypha lies alongside the host cell wall and extends intercellularly into the plant. During early phases of the disease, the pathogen is restricted to the middle lamellae, but later it degrades the host cell walls. The host protoplasm seems unharmed until a late stage of disease development. In a resistant plant, the initial infection pattern is the same as in a susceptible one, but the growth of the pathogen soon becomes arrested following the death of host cells in the vicinity of the infecting hypha. The mode of growth of the fungus is discussed in relation to earlier biochemical work on this disease.