The autecology and ultrastructural interactions between Mycosphaerella ascophylli Cotton, Lautitia danica (Berlese) Schatz, Mycaureola dilseae Maire et Chemin : and their respective marine algal hosts

• Main Author: Stanley, Susan J.
• Published: University of Portsmouth 1991
• Subjects: 580; Marine fungi ecology
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293098

Three species of higher algicolous fungi were examined at the autecologica1, cultural, light microscope, and scanning and transmission electron microscope levels. Fungal development and the host-parasite relationship are described for each association. The seasonal occurrence of marine fungi from intertidal populations of Dilsea carnosa, Ascophyllum nodosum and Chondrus crispus was examined at Bembridge, Isle of Wight, UK. A basidiomycete pathogen, Mycaureola dilseae, was found on D. carnosa, and two ascomycetes, Mycosphaerella ascophylli and Lautitia danica, on A. nodosum and C. crispus, respectively. Mycaureola dilseae is host specific and exhibited a limited reproductive cycle with green necrotic lesions and basidiomata observed only during September and October. Mycosphaerella ascophylli is an obligate endophyte of A. nodosum, an association in which the fungal and algal reproductive cycles were found to be synchronous with sporocarps confmed to host receptacles. This fungus is also found in Pelvetia canaliculata. Sporocarps of L. danica were recorded on cystocarpic C. crispus throughout the year, with a higher incidence of the fungus on older fronds. Tetrasporic C. crispus was also infected and in both cases the fungus was confmed to algal reproductive tissues. Mycosphaerella ascophylli was isolated from A. nodosum and P. canaliculata tissues and the anamorph, Septoria ascophylli was induced to sporulate. Growth of M. di/seae from D. carnosa lesions was limited and Lautitia danica could not be isolated from infected C. crispus tissues. Ascospore (L. danica and M. ascophylli) and basidiospore (M. di/seae) cultures did not grow beyond the germ tube phase. Hyphae of M. dilseae grew both inter- and intra-cellularly in D. carnosa. Penetration of algal cells was initially achieved by fme bifurcated penetration hyphae and there is evidence of mechanical pressure and localized enzyme action. The fungus caused a progressive breakdown of algal cell walls and cell contents; particularly evident was the damage to chloroplasts and dissolution of Floridean starch grains. Infection fmally resulted in the formation on necrotic lesions, each surrounded by a ring of basidiomata. Transmission electron microscopy showed the ascus of M. ascophylli to be bitunicate with a thick endoascus and thin ectoascus. Intra-membranous haustoria were occasionally observed in the outer cell wall of A. nodosum and P. canaliculata. Lautitia danica asci were bitunicate and ascospores were covered with a mucilagenous layer. Penetration of host cells caused extensive damage and blackening of host reproductive tissues. The relevance of these results are discussed in relation to algal pathology and marine fungal ultrastructure.