An Action Spectrum for Light Inhibition of the “Terminal Phase” of Photosporogenesis in the Fungus Stemphylium Botryosum

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Abstract
Photosporogenesis has two distinct physiological stages in Stem-phylium botryosum (a Deuteromycete). The first is an “inductive phase” which is stimulated by ultraviolet radiation and results in the formation of conidiophores, and the second phase (“terminal phase”) leads to the formation of conidia and is inhibited by light. An action spectrum for the inhibition of the “terminal phase” was determined by irradiating colonies with monochromatic light (10 nm band widths) from 240 to 650 nm. There are two principal peaks of effectiveness at 280 nm and 480 nm, however, all radiation from 240 to 650 nm at high enough dosages inhibited the “terminal phase.” The most effective range was from 240 to 510 nm. Conidia were not inhibited by light at 21 C, but at 25 and 28 C complete inhibition was evident. The length of darkness necessary for the completion of the “terminal phase” is temperature dependent and the higher the temperature the longer is the dark period necessary for conidium formation.