An action spectrum for photoinduced conidium (8). This latter group of fungi has been studied by Leach (9) and others (10, 11,15). Several action spectra have been reported for light-induced sporulation (1, 3, 5, 7, 9-11, 13, 15) Half-band widths of monochromatic radiations were measured with an UV wavelength distribution analyzer (UV-55, Japan Spectroscopic Co., Ltd. modified to cover 200-750 nm), and are given in Table I. They were all less than 9 nm. Intensity of monochromatic radiation was measured with a radiometer (RMA-8, Japan Spectroscopic Co., Ltd.). The radiometer was a calibrated vacuum thermopile having a quartz window and was coupled with a nanovoltmeter and AC amplifier. Measurements were made before and after the experiments and these were averaged.Irradiation. The Petri dish lids of 4-day-old colonies were replaced with thick black paper covers having windows (30 x 60 mm) of uncoated cellophane (Fig. 1). The hyphal fronts were marked on the bottom of the Petri dish to locate the region to be irradiated. Colonies were then placed on the optical bench designed to hold a Petri dish in a precise position for exposure to monochromatic radiation. The horizontal beam of radiation from the monochromator was directed through the uncoated cellophane onto the colony using a front surface aluminum mirror.Light intensities ranged from 15.2 to 4,448 erg/cm2 sec as shown in Table I. Exposure times ranged from 15 min to 2 hr. The spectroirradiator was located in a dark room controlled at 22 C.Temperature of the specimen chamber was kept at 22.5 + 0.5 C during irradiation. Unirradiated control cultures were handled similarly to the irradiated cultures but kept in darkness. None of the controls developed conidia. After irradiation, colonies were incubated in darkness for an additional 48 hr at 22.5 C to allow spores to develop.Spore Counts and Dose Response Curves. After the final incubation, samples were removed from the irradiated portion of a colony. These samples were 30 mm long at the irradiated perimeter of the colony and 10 mm wide. The sample was comminuted in 10 ml of distilled H20 with 0.1% Tween 20 by blending 60
In order to determine the effective spectral region for stimulating maturation of apothecia of Sclerotinia trifoliorum Erik., sclerotia embedded in sterilized soil were irradiated through coloured cellophane films in a green house under natural conditions or irradiated continuously by fluorescent lamps with glass filters. Radiation filtered throught colourless, blue, green or yellow cellophane films was effective in stimulating maturation of apothecia, while the radiation filtered through red cellophane was not. On the other hand, in the experiment with coloured fluorescent lamps not only red but also green and yellow lamps had no stimulative effect on maturation of apothecia. Studies with glass filters which cut off all radiations shorter than the wavelength designated for each filter indicated that near-ultraviolet radiation between 300 and 390nm stimulated apothecial maturation, whereas wavelengths longer than 390nm were not effective. From these results it can be concluded that the sporulation response to light of this fungus is similar to that of the fungus sensitive to near-ultraviolet radiation, and the effective radiation under green and yellow cellophane is due to transmission bands in near ultraviolet region.
An action spectrum for photoinduced conidium formation in the fungus Alternaria solani (Ellis et G. Martin) Sorauer was determined by exposing colonies to monochromatic radiation obtained from a diffraction grating monochromator. Reciprocity holds over a wide range of time and dose rate for wavelengths of 242 and 283nm. The most effective wavelength is around 230nm. Three peaks are evident in the action spectrum at around 230, 270 and 285nm, with definite shoulder at about 303nm. Another shoulder is dsicerned at around 240nm. The main trough is at 250 to 260nm. Wavelengths longer than 356nm were not effective in inducing conidium formation even at high dosages given by 6 hr continuous irradiation.
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