Variation in responses of spores of Septoria tritici and S. nodorum to UV-B irradiation in vitro

Abstract

The effect of UV-B radiation (280–320 nm) on germination of spores and extension of germ-tubes of Septoria tritici (two isolates from the U.K., two from Tunisia) and S. nodorum (two isolates from the U.K.) was examined in vitro . Germination of spores after 48 h incubation was unaffected in both species by 4 h irradiation per 24 h period (UV-B DNA , 3 kJ m −2 d −1 ), but was inhibited in S. nodorum by continuous UV-B irradiation (UV-B DNA , 18 kJ m −2 d −1 ). Germination was unaffected by background white light (400–700 nm) for 16 h per day. After 48 h in the dark, germ-tubes were longest in S. nodorum (both isolates) and shortest in the two Tunisian isolates of S. tritici . By comparison with continuous darkness, germ-tube extension in all isolates was strongly inhibited by continuous UV-B. Germ tube extension of the U.K. isolates, but not of the Tunisian isolates, was also inhibited by 4 h UV-B both with a dark background and within a 16 h white light day. The time in the 24 h cycle when germination started, i.e. incubation began, and when exposure to either UV-B radiation or white light occurred, affected the response of the fungi. Differences in sensitivity to UV-B between the S. tritici isolates suggest that adaptations to different fluxes in contrasting natural environments may occur.