Effects of temperature and incubation time on germination of ascospores of Leptosphaeria maculans and Leptosphaeria biglobosa in vitro

Ascospores of both L. maculans and L. biglobosa germinated on water agar at
temperatures from 5 to 20°C. After 2 h of incubation on water agar, some L. maculans ascospores had germinated at 10 to 20ºC and some L. biglobosa ascospores had germinated at 5 to 20ºC. The percentages of both L. maculans and L. biglobosa ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5 to 20ºC. The observed time (Vo50) which elapsed from inoculation until 50% of the spores had germinated was shorter for L. biglobosa than for L. maculans ascospores. Germ tube length increased with increasing temperature for both ascospore groups. Germ tubes from L. biglobosa ascospores were longer than germ tubes from L.maculans ascospores at all temperatures tested, but the mean diameter of germ tubes from L.maculans ascospores (1.8 ì m) was greater than that of those from L. biglobosa ascospores (1.2 ì m) at 15 and 20ºC. The average number of germ tubes produced from L. maculans ascospores (3.8) was greater than that from L. biglobosa ascospores (3.1) after 24 h of incubation at 20ºC. Germ tubes
originated predominantly from interstitial cells of L. maculans ascospores or terminal cells of L. biglobosa ascospores. Hyphae from L. maculans ascospores grew tortuously, whilst those from L. biglobosa ascospores grew in almost straight lines.