MORPHOLOGY AND DEVELOPMENT OF HYPERPLASIA ON CYSTOSEIRA OSMUNDACEA (PHAEOPHYTA) ASSOCIATED WITH HALOGUIGNARDIA IRRITANS (ASCOMYCOTINA)

The tissue of Cystoseira osmundacea (Tum.) C. Ag. (Fucales, Phaeophyta) undergoes pronounced developmental changes when in association with the fungus Haloguignardia irritans (Setchell et Estee) Cribb et Cribb (Sphaeriales, Ascomycotina). Nonmeristematic cortical cells are induced to divide and ultimately form a structure composed of tightly packed club-shaped projections. Each projection contains a single fungal ascocarp or spermogonium. A protective multilayered algal tissue surrounds the fungal reproductive structures. This association significantly alters algal morphology to the apparent protective advantage of the fungus. A LARGE NUMBER of marine algae are known to produce galls in association with foreign organisms ranging from bacteria to animals (Apt, 1988). These abnormal growths are characterized by host cell hypertrophy (enlargement) and hyperplasy (cell proliferation). Fungi associated with several obvious galls are species of Haloguignardia (Ascomycotina), which infect a number of species of brown algae. Worldwide, brown algal genera attacked by Haloguignardia spp. are Cystoseira, Halidrys, and Sargassum. Details on the taxonomy and morphology of this fungus have been previously reported (Estee, 1913; Kohlmeyer and Kohlmeyer, 1979; Kohlmeyer and Demoulin, 1981). The morphological changes of the algal host in association with Haloguignardia have not been examined. The purpose of this article is to describe at a light microscopic level the morphological changes of the host tissue, Cystoseira osmundacea (Turn.) C. Ag., infected with Haloguignardia irritans during gall development. MATERIALS AND METHODS -Samples of Cystoseira osmundacea with galls associated with Haloguignardia were collected from the vicinity of Pigeon Pt., California in the fall of 1983. Samples were immediately preserved in 3% formaldehyde-seawater (pH 7.0) for later examination. Preserved samples for microscopic examination were prepared for embedding in N-buI Received for publication 28 April 1987; revision accepted 15 September 1987. The author would like to thank Drs. A. Gibor, M. Moseley, B. Sweeney, and M. Neushul for their assistance and advice. This work was partially supported by a Regents Fellowship from the University of Califomia. tylmethacrylate and paraffin. Dehydration was first accomplished by replacing the fixative with 10% steps of EtOH until the final concentration was 50% alcohol. After 24 hr the material was transferred to 100% 2,2 dimethoxypropane and 1 N HCL was then added at a ratio of 1:10. This solution cooled spontaneously. After return to room temperature, the solution was removed and the procedure repeated, four times. The material was then transferred into two changes of 100% Dioxane for 60 minutes each. After dehydration, the material was embedded in N-butylmethacrylate and paraffin following the procedure of Engen and Wheeler (1978). Serial sections 5-8 gm thick were cut on a rotary microtome and stained with 1% thioin. RESULTS-The coastal intertidal zone between San Francisco and Monterey Pennisula, California was surveyed for the presence of Haloguignardia associated galls (Fig. 1-4) on Cystoseira osmundacea. Only two locations, Pigeon Pt. and Carmel Bay, were consistently found to have populations of Cystoseira with galls. Even at these areas not all thalli were infected, only a small percentage (< 5%) ofthalli bore one or more infections. Galls were found on most portions of the thalli including the perennial stipe, vegetative fronds and annual fertile fronds. Holdfasts were not observed to bear galls. Only about 20% of galls were clearly associated with broken or torn fronds. The infections showed no visible sign of dead or decomposing tissue associated with the presence of galls. There was a tendency for galls found on fronds to be located near or at the midrib (Fig. 2, 3). The outer surface of normal Cystoseira tissue (Fig. 5) consists of a meristoderm composed