Effects of Ultraviolet Radiation upon Representative Species of Fusarium

Abstract

Four-day old cultures of 59 authentic species, varieties and forms of Fusarium were exposed (at a distance of 40 cm.) to the u.-v. rays transmitted by a Cooper-Hewitt quartz mercury-arc lamp. When given a 15-min. exposure on 3 successive days through filters transmitting waves as short as 2650 A. but no shorter than 2300 A., many strains responded with an increase in macrospore per-centage, and in most of the strains tested there was an increase in total sporulation (macrospores and/or micro-spores). This increase was evidenced by production of pionnotes or of sporodochia, or by greater intensity of mycelium, stroma and spore mass colors. Some spp. gave a constant, very striking increase in macrospore percentage under treatment, others gave less striking increase, while still others characteristically failed to respond with greater macrospore production. With these unresponsive spp. there was no cumulative increase in macrospore percentage due to repeated irradiation, although the quantity of spores present could be thus increased. Some spp. which had never sporulated in the laboratory or which were in "abkultur" produced abundant normal macrospores after irradiation. Initiation of sporulation was hastened in others. All responsive spp. showed increased macrospore percentage under vita-glass filters (lower limit 2650 A.) but some gave maximum production under Corex filter 980A(2300 A.) or Corex 986 A(2535 A.). The most extensive macrospore production induced by irradiation occurred in sapro-phytic and decay producing spp. of sections Sporo-trichiella, Gibbosum, Discolor subsection Saubinetii, Martkila, and Elegans subsection Oxysporum. The vascular parasites failed to show appreciable macrospore increase as a result of irradiation. Increased macrospore production did not seem to be directly correlated with inhibition in growth rate. Exposure directly to the Hg arc transmitting to 2230 A. resulted in decreased growth rate, colony stunting and injurious effects to mycelium and spores in all spp.; but most forms were injured slightly or not at all by exposure to waves transmitted through the filters. Filters transmitting no u.-v. did not affect sporulation. 14 spp. with known perfect stages were treated but perithecial production was not induced either by throe 15-min. exposures through vitaglass at 40 cm. from the arc or by 3 (or less) 4-second direct exposures at 21 cm. It is believed the responses to u.-v. are sufficiently characteristic to be useful as an additional physiological response in taxonomic studies. The value of this method for producing macrospores in some spp. is unquestionable.