ACTION SPECTRA FOR LIGHT-INDUCED SPORULATION OF THE FUNGI PLEOSPORA HERBARUM AND ALTERNARIA DAUCI*,†

Abstract— Action spectra for light induced sporulation were determined for conidia of Alternaria dauci , and conidia and perithecia of Pleospora herbarum (Imperfect stage is Stemphylium botryosum ). Only radiation less than 370 mμ induced formation of conidia, and less than 390 mμ formation of perithecia. The action spectra showed increased effectiveness in the 230 and 290 mμ regions, and possibly in the 260–270 mμ regions. Below 280 mμ these action spectra may not be representative of the "true" absorption spectra of the photoreceptors involved because of possible superimposed effects caused by nucleic acid absorption. Though the action spectra were not identical, the number of characters in common were suggestive of a similar photoreceptor. Similarities between action spectra for sexual and asexual reproduction of P. herbarum indicate the possibility of a single photoreceptor for both processes.