An action spectrum for photoinhibition of conidium formation in the fungus Alternaria solani

An action spectrum for photoinhibition of conidium formation in Altemaria solani (Ellis et G. Martin) Sorauer was determined by exposing colonies to monochromatic radiation between 232 and 722 nm. Following photoinduction of conidiophores by near-ultraviolet radiation, inhibitory exposures were made 5–7 h into the dark period, using monochromatic radiation. Radiation longer than 530 nm was not effective for inhibiting conidium formation. The action spectrum has maxima at 480, 455, and 435 nm in the visible region, 381 nm in the near-ultraviolet region, and 273 nm in the far-ultraviolet region. The action spectrum is divided into three parts by two troughs at 303–316 nm and 396–415 nm. These characteristics of the action spectrum indicate that the photoinhibition of conidium formation is a typical blue photoresponse with an increased activity in the far-ultraviolet region.