Browsing by Author "CORREA, JA"

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    DEFORMATIVE DISEASE IN IRIDAEA-LAMINARIOIDES (RHODOPHYTA) - GALL DEVELOPMENT ASSOCIATED WITH AN ENDOPHYTIC CYANOBACTERIUM
    (1993) CORREA, JA; FLORES, V; SANCHEZ, P
    This study is the first report of an algal disease, developed in close association with an endophytic organism, documented for the southeastern Pacific. We describe a disease affecting wild populations of the red alga Iridaea laminarioides Bory in central Chile, characterized by gall developments on the surface of sporophytic, cystocarpic, and immature thalli. These abnormal growths result in severe morphological alterations of the affected thalli. Diseased fronds display an aggregated spatial distribution and occur throughout the year, with a maximum in summer followed by a decline in winter. The presence of galls was not associated with broken or torn fronds. Although causality has not been unequivocally demonstrated, our field and laboratory observations indicate a strong association of the galls with infections by an endophytic cyanobacterium, probably belonging to the genus Pleurocapsa.
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    ENDOPHYTIC ALGAE OF CHONDRUS-CRISPUS (RHODOPHYTA) .5. FINE-STRUCTURE OF THE INFECTION BY ACROCHAETE-OPERCULATA (CHLOROPHYTA)
    (1994) CORREA, JA; MCLACHLAN, JL
    The sequence of events taking place during infection of the algal host Chondrus crispus by the algal endophyte Acrochaete operculata was characterised at the ultrastructural level. Infection required settlement of quadriflagellate zoospores on the outer cell wall of the host. The host outer cell wall did not represent a barrier against penetration by the endophyte, which digested its way through. The extent of further spread of A. operculata in C. crispus was determined by the life-history phase of the host. In sporophytic fronds, colonisation of inner tissues occurred by digestion of the intercellular matrix, and infection spread throughout the frond. In gametophytic thalli, infection remained localised, forming a characteristic papule. In spite of these differences, degenerative changes at the cellular level were similar in the two phases of the host. Damage was caused by compression and by penetration of host cells. Final breakdown of the host resulted from the combined effects of A. operculata and bacteria. Bacteria alone did not cause damage to healthy C crispus, but they accelerated cell wall degradation in the presence of A. operculata. Thus, A. operculata should be considered a primary pathogen of C. crispus, causing direct cellular damage and facilitating secondary infections.
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    GREEN PATCH DISEASE IN IRIDAEA-LAMINARIOIDES (RHODOPHYTA) CAUSED BY ENDOPHYTON SP (CHLOROPHYTA)
    (1994) CORREA, JA; FLORES, V; GARRIDO, J
    A green mottled coloration, or green patch disease, develops in the red alga Iridaea laminarioides Bory when it is infected by the algal endophyte Endophyton sp. The disease is widespread in host populations along the coast of central and southern Chile (33-degrees-17' S to 40-degrees-33' S) and affects both gametophytic and sporophytic fronds. It is characterized by green areas, usually located at the base of the thalli, which become soft in texture in fully developed infections. The softening of the host tissue is caused by cellular destruction resulting from endophyte-mediated compaction of the cells, followed by secondary bacterial infections. Bacteria gain access to the host through openings left in the host thallus during spore release from mature sporangia of Endophyton. Both life-history phases of L laminarioides were successfully infected by unialgal isolates of Endophyton in laboratory trials. Infection was achieved only by germlings from newly settled spores and the process of penetration was completed within 3 d. Softening of laboratory-infected thalli became evident about 8 wk after penetration and thallus destruction was complete after 3 to 4 mo of culture.
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    SORUS-SPECIFIC EPIPHYTISM AFFECTING THE KELPS LESSONIA-NIGRESCENS AND L-TRABECULATA (PHAEOPHYTA)
    (1993) MARTINEZ, E; CORREA, JA
    This study characterizes a tissue-specific association between the green algal epiphyte Sporocladopsis sp. and the sori of its kelp hosts, Lessonia nigrescens Bory and L. trabeculata Villouta et Santelices, occurring on the Pacific coast of Chile. The hypothesis that the distribution pattern of the epiphyte was due to constitutive features of the host was assessed by combined field and laboratory observations. Results showed that the epiphyte was confined to sori of L. nigrescens and L. trabeculata, failing to invade adjacent vegetative tissues. Infected hosts were found in northern and central Chile, reaching an incidence of 100 % in low intertidal plants of L. nigrescens, Although important modifications in microtopography develop on the surface of the mature sorus of L. nigrescens, colonization by the epiphyte occurs rather early, on immature sori with only minor surface changes. Thus, microtopographical changes per se do not appear as the only explanation for the observed distributional pattern. The absence of periodical renewal of the outer.cell wall by the reproductive tissue, in contrast with its continous removal in the vegetative tissue, provides a complementary mechanism that explains the restricted distribution of the epiphyte. In the field, growth, reproduction of the epiphyte, and infection of new tissue of L. nigrescens was accomplished in 3 wk. In the laboratory, the epiphyte was successfully isolated, and grew to maturity within 1 mo.
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    WHITENING, THALLUS DECAY AND FRAGMENTATION IN GRACILARIA-CHILENSIS ASSOCIATED WITH AN ENDOPHYTIC AMEBA
    (1995) CORREA, JA; FLORES, V
    Whitening of Gracilaria chilensis, accompanied by tissue softening and thallus fragmentation, was found to be associated with the presence of an endophytic amoeba. Although the symptoms developed originally in green mutant thalli, subsequent infections in the laboratory also affected normal, wild-type G. chilensis. Ultrastructural evidence indicates that the amoebae perforate the host cell walls of both cortical and medullary cells and digest their protoplasm. Feeding by the amoeba appears to involve both phagocytosis and enzymatic digestion of the host tissue. Destruction of the host tissue resulted in large cavities first, followed by thallus fragmentation. No other organism was found during the early stages of thallus invasion by the amoeba, although bacteria may appear once the amoeba reaches the inner tissues of the host.