The Qualitative and Quantitative Relationship of Monochromatic Radiation to Sexual and Asexual Reproduction of Pleospora Herbarum

SUMMARY

The electromagnetic radiation requirements for the induction of the sexual (perithecia) and asexual (conidia) reproduction in Pleospora herbarum (status imperfectus Stemphylium botryosum) were determined with monochromatic radiation in the visible and ultraviolet wave lengths at intensities of 100 and 300 μw/cm². Colonies were irradiated at 2378 Å, 2537 Å, 2803 Å, 3131 Å, 3663 Å, 4046 Å and 5461 Å (band width 132 Å) over exposures ranging from a minimum of 1/50 second to a maximum of 20,000 seconds. Conidia were induced by wave lengths 2378 to 3663 Å inclusively, but not by longer wave lengths. Two wave lengths, 2378 Å and 3131 Å, appeared to be most efficient in inducing conidial production over a wide range of exposures. Wave lengths effective in inducing perithecial formation were in general quite similar to those for conidia, though a few perithecia were initiated at 4046 Å but none at 5461 Å. The initiation of both sexual and asexual reproductive processes was dependent on wave length, length of exposure and intensity. The dosages necessary to induce reproduction decreased with decreasing wave length. Dosages causing inhibition of sporulation were similarly dependent on wave length, length of exposure and intensity and were least at high intensities and at the shorter wave lengths. The qualitative and quantitative radiation requirements for sexual and asexual reproductive processes though fairly similar showed some marked differences: lower dosages were adequate for both the induction and the inhibition of perithecia than for conidia; the wave lengths effective in inducing perithecia extended slightly further into the visible spectrum than for conidia; wave lengths of 2378 and 3131 Å were most efficient for producing conidia, but not for perithecia.

The location of perithecia in relation to the surface of the medium was also related to wave length and dosage. With increase in dosage and decrease in wave length, perithecia tended to form submerged in the medium.

Qualitatively and quantitatively, the radiation requirements for the induction of conidial production in P. herbarum were almost identical with those previously reported for Ascochyta pisi. It is suggested, therefore, that a similar photoactivated reproductive mechanism is probably involved in these two species of fungi.