The Effect of Light and Darkness Upon Infection of Asterionella formosa Hassall by the Chytrid Rhizophydium planktonicum Canter emend

Observations, both experimental and microscopic, indicate thatzoospores of Rhizophydium planktonicum Canter emend., can remainalive, but rarely become adherent upon cells of Asterionellaformosa Hassall under conditions of very low light or in completedarkness. The behaviour patterns of zoospores towards host cells underdarkened conditions were compared with those which took placeunder well illuminated conditions leading to the settlementof zoospores on host cells. The differences noted may help toexplain the lack of zoospores found upon inadequately illuminateddiatom cells. Some evidence suggests that young zoospores lack the abilityto adhere to host cells. After the encystment of zoospores uponAsterionella cells in the light, their further growth and developmentcan continue in darkness. Rhizophydium planktonicum Canter emend., Asterionella formosa Hassall, chytrid, diatom, infra-red illumination, zoospore