An Action Spectrum for Light Inhibition of the "Terminal Phase" of Photosporogenesis in the Fungus Stemphylium botryosum

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Abstract
Two distinct physiological stages of photosporogenesis are evident in S. botryosum. The 1st stage is stimulated by UV radiation and results in the formation of conidiophores; and 2nd ("terminal phase") leads to the formation of conidia and is inhibited by light. An action spectrum for inhibition of the "terminal phase" was determined by irradiating colonies with monochromatic light (10 nm band widths) from 240 to 650 nm. Two principal peaks of effectiveness occurred at 280 nm and 480 nm, though all radiation from 240 through 650 nm was inhibitory at high enough dosages. The most inhibitory range was from 240 to 510 nm. Conidia were completely inhibited by light at 25[degree] and 28[degree]C, but not at 21[degree]C. The length of darkness necessary for completion of the "terminal phase" is temperature-dependent, and the higher the temperature the longer is the dark period necessary for conidium formation.