Mycol. Res. 92 (3): 293-296 (1989) Printed in Great Britain Effect of ultraviolet irradiation on germination and growth Aspergillus flavus and Penicillium notatum MOHAMED OSMAN, M. A. ELSAYED, Y. A. H. MOHAMED AND A. M. ABO-ZEID Department of &tany, Faculty of Science, Tanta University, Tanta, Egypt Effect of UV-irradiation on germination and growth in Aspergillus f/avus and Penicillium notatum. Mycological Research 92 (1): 293-296 (1989). . In 293 Uv-A (366 nm) irradiation delayed germination of conidia in Penicillium notatum and Aspergillus f/avus. The inhibitory effect was dependent on the exposure period and maximum inhibition was obtained after irradiation for 4 h. The length of developed germ- tubes was reduced by the same treatment. Uv-B irradiation (240-280, peak 254 nm) was more effective than uv-A. Irradiation for 30 min completely inhibited conidial germination in P. notalum while 40 min exposure caused complete inhibition in A. f/avus. The development of germ-tubes was very slow after uv-B irradiation. Linear growth was also affected by uv-A especially if irradiation was applied for long periods. Retardation in linear growth was most pronounced during the first 3 d incubation. Uv-B irradiation markedly affected growth and a delay of 72 h in growth could be observed in some treatments. Uv-B irradiation for 4 h completely inhibited growth of P. notatum, while the same treatment retarded growth to some extent in A. f/avus. Key words: Penicillium notatum, Aspergillus f/avus, UV-irradiation, Radial growth, Conidial germination. Micro-organisms respond to light in different ways: by changed growth, spore production, pigment formation and other responses (Carlile, 1965, 1970). In nature most fungi are exposed to a little uv-B radiation and considerable uv-A and visible radiation. The effects of light (uv and visible) on fungi are quite diverse. Hill (1976) found that light induced conidiation and inhibited growth in Aspergillus ornatus and Harda (1975) reported that conidial germination and germ- tube growth of Monilinia mali were inhibited by light to a certain extent. Saltarelli & Coppola (1979) reported that black- uv inhibited cell growth in Candida albicans and Osman & Valadon (1979, 1981) observed that growth and conidial germination of Verticillium agaricinum were markedly inhibited by uv-A and black light. Page (1952) found that light strongly inhibited the mycelial growth of Pilobolus and Lucas, Kendrick & Givan (1975) reported inhibition of germination of Puccinia graminis f.sp. tritici urediniospores by continuous irradiation. The killing effect of uv-B was observed by Fraikin, Pospelor & Rubin (1976) in the yeast Candida guilliermondii. The object of the present investigation was to study the effect of uv irradiation on conidial germination and growth of Aspergillus f/avus and Penicillium notatum (both with coloured conidia) and to compare these with other fungi with colourless conidia. MATERIALS AND METHODS The fungal strains were isolated from Egyptian soil and identified as Aspergillus f/avus and Penicillium notatum. Both fungi were maintained on Czapek Dox agar medium. Spore germination was studied in Petri dishes containing 20 ml of 2 % water agar, divided into squares of I cm 2 • One drop (0-05 ml) of conidial suspension from a 7-day-old dark- grown culture was placed on each square and Petri dishes were then placed under uv-A and uv-B sources for different periods. The source of uv-A consisted of two F8 TS/BLB USA 20 W lamps (366 nm) while the uv-B source was Astralux Quartz lamps 30 W (240-280, peak 254 nm). The distance from both sources of irradiation was adjusted to obtain irradiance of 0-4 W m- 2 (irradiance was measured by LI-185 Quantum/Radiometer/Photometer, LICOR Ltd, U.S.A.). After irradiation, Petri dishes were incubated in the dark at 24-25 dc. Two blocks of agar were removed at various time- intervals, stained with lactophenol blue and four microscopic fields per block examined for germinated conidia, giving a total of eight readings per treatment. The percentage germination of each treatment was compared with that of the dark control. Samples which appeared to be inhibited were re-examined after a longer period of incubation in the dark to determine whether the inhibition was temporary or complete. Colony radial growth was studied in Petri dishes containing 20 ml Czapek Dox agar. A loopful of 7-day-old dark-grown culture (on Czapek Dox medium) was placed in the centre of each Petri dish, irradiated for different periods under uv-A or uv-B sources and then incubated in the dark for 7 days at 24-25 0 • Colony diameter was measured daily during the incubation period. All experiments were carried out at least three times.