A Narrow Range of Wavelengths Active in Regulating Apothecial Development in <i>Sclerotinia sclerotiorum</i>

Abstract Three Swedish and one Canadian isolate of Sclerotinia sclerotiorum were tested for apothecial formation in light of different wavelengths and for measuring light absorbance of macerated apothecia and apothecia filtrate in a spectrophotometer. The apothecial formation was recorded after keeping laboratory‐produced sclerotia under different light filters illuminated by True‐Lite fluorescent tubes. The experiments, performed at room temperature, demonstrated that normal apothecia developed only in light of wavelengths between 276 and 319 nm, and that macerated apothecia and apothecia filtrate absorbed light at the same wavelengths with a maximum absorbance at 310 nm. The stipes showed a clear positive phototropism in light that was not essential for apothecia development. indicating that there may be different photoreceptors for phototropism and photomorphogenesis. Negative phototropism of stipes occurred at certain wavelengths in yellow light.