Morphology of Erysiphe pisi on leaves of Pisum sativum

Morphological details of conidium germination, hyphae, appressoria, conidiophores, and organisation within colonies of Erysiphe pisi on leaves of Pisum sativum were studied in frozen, hydrated specimens with a scanning electron microscope. The pathogen has several adaptations to enable efficient colonisation of host leaf surfaces, including production of several hyphae from each germinated conidium, unidirectional growth of individual hyphae, prolific hyphal branching at obtuse angles to lines of hyphal growth, and rapid and prolific development of appressoria and conidiophores. Hyphal cells on leaf surfaces are specialised to produce either appressoria or conidiophores and hyphal branches.